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FRIEND 2002—REGIONAL HYDROLOGY:Bridging the Gap between Research and Practice edited by Henny A. J. van Lanen & Siegfried Demuthco-editors: E. Servat, R. Ibbitt, C. Prudhomme, M. F. Bari, D. Hughes, M. del Carmen Llasat & S. H. MkhandiIAHS Publication no. 274 (published March 2002) in the IAHS Series of Proceedings and ReportsISBN 1-901502-81-3; 518 + x pp.; price £73.50The International FRIEND research programme (Flow Regimes from International Network Data) is an initiative of the International Hydrological Programme of UNESCO which brings together people from a range of institutions including operational hydrological agencies, water users, policy makers and research scientists, to generate and share scientific knowledge, tools and information. One of the main objectives of FRIEND is to study the variability of hydrological regimes in order to improve the management of water resources at the catchment, regional and global scale. Since the inauguration of FRIEND in 1985, the initiative has grown to a worldwide network of scientists belonging to different regional FRIEND groups: Northern European, Alpine and Mediterranean, Southern Africa, West and Central Africa, Hindu-Kush Himalayan, Nile Basin, Asian Pacific and Caribbean.

This volume comprises selected and reviewed papers presented at the Fourth International Conference on FRIEND held in Cape Town, South Africa in March 2002. The conference focused attention on bridging the gap between knowledge, research and practical applications; the themes were:– Hydrological Data policy, international rivers, databases, real time, dissemination– Managing hydrological risk floods, surface and groundwater droughts– Water scarcity overexploitation and poverty reduction– Sustaining water-related ecosystems definitions, methodology and operation– Continental hydrology regimes, water sharing, teleconnections, snow, ice, international basins

The 63 papers demonstrate how advances in hydrology can be used for the development of integrated river basin management to ensure the sustainable development of water resources. Furthermore, examples are given of the incorporation of research results into operational

hydrology and water resources planning, including numerical and statistical models and visualization techniques.

Contents

Preface by Henny A. J. van Lanen & Siegfried Demuthv1 Keynote PapersFRIEND: an international network for bridging the gap between research and practice Alan Gustard3Regional water resource assessments in the SADC region Denis Hughes, Andre Görgens, Brian Middleton & Brian Hollingworth11The European Water Framework Directive—an example for water management in national and international river basins Jörg Ringeltaube19Management of water resources for poverty alleviation in the Hindu-Kush Himalayas Suresh R. Chalise272 Hydrological DataUpgrading a conventional hydrological information system—an Indian example H. Chowdhary, S. K. Jain & H. J. M. Ogink35The development of an information modelling system for regional water resource assessments Denis Hughes43Detection of intensification of the global water cycle: the potential role of FRIEND Alan D. Ziegler, Justin Sheffield, Eric F. Wood, Bart Nijssen, Edwin P. Maurer & Dennis P. Lettenmaier

513 Managing Hydrological Risks: Climate VariabilityStatistical analysis of at-site extreme rainfall processes in Peninsular Malaysia Zalina Mohd Daud, Amir Hashim Mohd Kassim, Mohd Nor Mohd Desa & Van-Thanh-Van Nguyen

61Climatic and anthropogenic impacts on the flow regime of the Nakambe River in Burkina Faso G. Mahé, A. Dray, J. E. Paturel, A. Cres, F. Kone, M. Manga, F. N. Cres, J. Djoukam, A. Maiga, M. Ouedraogo, D. Conway & E. Servat

69Analysis of basin response resulting from climate change and mitigation measures Erik P. Querner77Hydrological drought studies in the wide context of climate variability Ladislav Kašpárek & Oldřich Novický85Scenarios assessing the influence of climate variability on drought in Europe Kerstin Stahl, Birgit Hassler & Siegfried Demuth93Temporal variability of recharge as an indicator for natural groundwater droughts in two climatically contrasting basins Henny A. J. van Lanen & Elisabeth Peters

1014 Managing Hydrological Risks: RisksImpact of climate change on flooding in the UK: a methodology for estimating uncertainty Christel Prudhomme, Dörte Jakob & Cecilia Svensson109Modelling of flood flows in Rufiji River basin, Tanzania Simon H. Mkhandi, Raj Kachroo & Felix Mtalo117Prédétermination régionale des débits de crue. Cas de la zone méditerranéenne française Jacques Lavabre, Nathalie Folton, Catherine Fouchier & A. Faure-Soulet123Flood-plain inundation based on coupled hydraulic and GIS models Urszula Soczynska, Artur Magnuszewski, Barbara Nowicka & Jan Jelowicki131Estimating design floods for small earth dams in Malawi M. P. McCartney, A. B. Chirwa & H. A. Houghton-Carr139Conséquences de la sécheresse observée depuis le début des années 1970 en Afrique de l’Ouest et centrale: normes météorologiques et hydrologiques Mahaman Ouedraogo, Jean-Emmanuel Paturel, Gil Mahé & Eric Servat

149Management of drought risk in the Sudano-Sahelian region of Nigeria Olusegun Adeaga157Changes in the hydrological response of two Sicilian basins affected by fire Giuseppe Aronica, Angela Candela & Mario Santoro1635 Managing Hydrological Risks: MethodsRegionalization for one to seven day design rainfall estimation

in South Africa Jeffrey Smithers & Roland Schulze173Methods for identifying and monitoring river flow drought in southern Africa Jeremy Meigh, Emma Tate & Matthew McCartney181Towards rainfall–runoff models that do not need calibration to flow data Richard Ibbitt & Ross Woods189Redéfinition des fonctions de production des modèles globaux de relation pluie–débit en milieu semi-aride africain Sandra Ardoin, Alain Dezetter, Eric Servat & Claude Bocquillon

197On-line short-term streamflow forecasting using neural networks Mohd Yusoff Mashor205Frequency analysis models for long hydrological time series in Southeast Asia and the Pacific region Joesron Loebis213Modélisation débit–durée–fréquence appliquée aux grands bassins versants du Burkina Faso Amadou Lamine Mar, Philippe Gineste, Hamattan Mohamed, Aly Tounkara, Ludovic Tapsoba & Pierre Javelle

221Coupling limited area models with distributed hydrological models for flood forecasting: the Toce basin case study Nicola Montaldo, Vania Toninelli, Marco Mancini & Renzo Rosso

229Development of flood boundary maps of urban areas using HEC-RAS software K. Brych, F. Dittrt & V. Elias237Regional analysis of the generation of extreme floods Stefan Uhlenbrook, Andreas Steinbrich, Dörthe Tetzlaff & Chris Leibundgut243GIS-based development of regional low-flow analysis for southern Taiwan Yu Pao-Shan & Shih Min-Luen251Regionalization of low-flow frequency estimates for rivers in northwest Bangladesh M. Fazlul Bari & Sabina Sadek257Groundwater runoff separation—test of applicability of a simple separation method under varying natural conditions Ladislav Holko, Andreas Herrmann, Stefan Uhlenbrook, Laurent Pfister & Erik P. Querner

265Meteorological droughts focused on a pan-European context Maria João Santos, Raquel Veríssimo, Sónia Fernandes, Marco Orlando & Rui Rodrigues273Handling non-extreme events in extreme value modelling of streamflow droughts Hege Hisdal, Lena M. Tallaksen & Arnoldo Frigessi281Modelling summer and winter droughts as a basis for estimating river low flows Gregor Laaha289Noise level estimation of chaotic hydrological time series A. W. Jayawardena, Xu Penchang & Bellie Sivakumar2976 Water ScarcityTreaty on sharing the Ganges waters: a milestone towards regional cooperation for development and management of water resources Md. Azizul Haque307Sustainable management of water resources in an agriculturally developed region of the Indo-Gangetic ecosystem, India R. B. Singh315River water sharing: India’s problems K. S. Murty323Water sharing in the Volta basin Marc Andreini, Paul Vlek & Nick van de Giesen329Vers une approche globale de la gestion de la ressource comme solution aux crises d’eau des dernières décennies au Cameroun Luc Sigha-Nkamdjou, Daniel Sighomnou & Gaston Lienou

337Déficit, adéquation de l’offre et de la demande en eau et dynamique du bassin de l’Anambé Adrien Coly, Honoré Dacosta & Pape Ousmane Soumaré3457 Sustaining Water-related EcosystemsManaging the fragile hydrological ecosystem of the northeast hilly region of India for resource conservation and improved productivity U. C. Sharma357Sustaining wetland ecosystems in the West and central African Sahel Lekan Oyebande365Modelling of regional changes of riverine nitrogen flow in the Svartå River, Sweden Lotta Andersson & Berit Arheimer373Caractéristiques hydrologiques et géochimiques d’un bassin élémentaire en zone tropicale humide d’Afrique: le bassin versant expérimental de Nsimi–Zoétélé (sud-Cameroun) Jules Remy Ndam Ngoupayou, Jean-Jacques Braun, Jean-Loup Boeglin, Michel Meybeck, Luc Sigha Nkamdjou, Daniel Sighomnou & Jean-Pierre Bedimo

381Extreme stages of the basin wetness conditions. Variability of the soil moisture in a lowland basin Urszula Somorowska389A compensatory forestry approach to clearing alien invasive vegetation from riparian zones in a South African basin G. P. W. Jewitt, M. C. Horan & K. B. Meier397Sustaining water-related ecosystems—the role of in-stream bedform design in river channel rehabilitation Nicholas J. Clifford, Philip J. Soar, Joanne C. Emery, Angela M. Gurnell & Geoffrey E. Petts

4078 Continental Hydrology Regimes: RegimesHimalayan glaciers meltdown: impact on south Asian rivers Syed Iqbal Hasnain417Flow regime characteristics of Himalayan river basins in Nepal Sunil R. Kansakar, David M. Hannah, John Gerrard & Gwyn Rees425Application of the regional flow estimation method in the Himalayan region Gwyn Rees, Karen Croker, Maxine Zaidman, Gwyneth Cole, Sunil Kansakar, Suresh Chalise, Arun Kumar, Arun Saraf & Mukesh Singhal

433Change of hydrological regimes over the central part of European Russia resulting from climate variations S. A. Zhuravin441Evidence d’une modification du régime hydrologique du fleuve Niger à Niamey Abou Amani & Madjyara Nguetora449Spatial and temporal variability of UK river flow regimes Donna Bower & David M. Hannah4579 Continental Hydrology Regimes: ClimateRégionalisation de la pluviométrie sur l’espace riverain de l’océan Indien et prévision statistique à moyen terme Bertrand Duchiron & Gérard Beltrando467The hydrological effects of two extreme rainfall events over East Africa: 1961 and 1997 Declan Conway475Space–time rainfall variability in West Africa derived from observations and GCMs Hubert Onibon, Thierry Lebel & Abel Afouda483Evidence of scaling properties in West African rainfall Abel Afouda, Thierry Lebel, Hubert Onibon, William Sacher, Luc Le Barbe, Christian Depraetere & Gregoire Ale

491La variabilité spatio-temporelle des précipitations au Sénégal depuis un siècle Honoré Dacosta, Konate Yaye Kandia & Raymond Malou499Stabilité interannuelle des précipitations en Côte d’Ivoire de 1950 à 1996 S. Bigot, T. Brou Yao, V. Bonnardot & E. Servat507Key word index515

AbstractsFRIEND 2002—Regional Hydrology: Bridging the Gap between Research and Practice (Proceedings of the Fourth International FRIEND Conference held at Cape Town, South Africa, March 2002). IAHS Publ. no. 274, 2002, pp. 3–10.

FRIEND: an international network for bridging the gap between research and practice

ALAN GUSTARDCentre for Ecology and Hydrology, Wallingford, Oxfordshire OX10 8BB, UKe-mail: [email protected]

Abstract The paper summarizes the key global issues of the twenty-first century, including population growth, environmental change, management of increasingly scarce resources, international development and environmental policy. The FRIEND (Flow Regimes from International Experimental and Network Data) programme is a global research network with over 75 participating countries. Examples of practical FRIEND research outputs are presented, together with a number of constraints and opportunities for transferring research to the user community. The FRIEND network is in a strong position to bridge the gap between research and practice but this will require developing closer partnerships with the user community and more actively implementing the process of technology transfer.Key words water resources; livelihoods; technology transfer; networks

FRIEND 2002—Regional Hydrology: Bridging the Gap between Research and Practice (Proceedings of the Fourth International FRIEND Conference held at Cape Town, South Africa, March 2002). IAHS Publ. no. 274, 2002, pp. 11–18.

Regional water resource assessments in the SADC region

DENIS HUGHESInstitute for Water Research, Rhodes University, Grahamstown 6140, South Africae-mail: [email protected]

ANDRE GÖRGENSNinham Shand Inc., PO Box 1347, Cape Town 8000, South Africa

BRIAN MIDDLETONSRK, PO Box 55291, Northlands 2116, South Africa

BRIAN HOLLINGWORTHDevelopment Bank of Southern Africa, PO Box 1234, Halfway House, South Africa

Abstract The paper outlines a proposed study to assess the available water resources of the South African Development Community (SADC) region in a unified way. This is considered essential given the increasing need for integrated (across national boundaries and economic sectors) management of the regions water resources. The proposed assessment is based on the regionalization of rainfall–runoff model parameters (over about 10 000 sub-basins at scales of 100–2500 km2) and modern database storage and retrieval methods and is expected to have a large capacity building component. While the project is ambitious, given the existing capacity within the region, the long-term benefits are considered to be more than worthwhile the effort.Key words South African Development Community (SADC); rainfall–runoff modelling; databases; capacity building


The European Water Framework Directive—an example for water management in national and international river basins

JÖRG RINGELTAUBEMinistry for Environmental Protection, PO Box 4107, D-30041 Hanover, Germanye-mail: [email protected]

Abstract Waters in the European Community are under increasing pressure from the continuous growth in demand for sufficient quantities of good quality water for all purposes. It is therefore necessary to develop an integrated Community policy on water. The success of this policy relies on close cooperation and coherent action at Community, Member States and local level as well as on information, consultation and involvement of the public, including users. The objective of achieving good water status needs to be pursued for the whole river basin, so that measures in the same ecological, hydrological and hydrogeological system are coordinated. International river basins like the Rhine basin serve as a positive example for this approach to water management, with their cooperation and joint settings of objectives across Member State borders and even beyond Member States of the European Union (EU).Key words European Community; Water Framework Directive; river basin management; good water status; Management Plan; combined approach; information management; European GIS


Management of water resources for poverty alleviation in the Hindu-Kush Himalayas

SURESH R. CHALISEMountain Natural Resources Division, International Centre for Integrated Mountain Development (ICIMOD), PO Box 3226, Kathmandu, Nepale-mail: [email protected]

Abstract For the people living in the remote and inaccessible mountainous region of the Hindu-Kush Himalayas (HKH), year-round availability of water is a major problem. Over the last few decades development interventions have ignored the water needs of mountain communities, their traditional institutions and

indigenous knowledge of water management. This has contributed to stagnant food production in the face of increasing population, leading to abandonment of land, migration out of the area and growing poverty of people. Policy reorientation to provide incentives for investment in participatory water harvesting and management systems can contribute to poverty alleviation in the Hindu-Kush Himalayas, in which international scientific programmes and donor communities can play an important role by providing support to national and regional initiatives.Key words Hindu-Kush Himalayas; water policy; water harvesting; poverty alleviation


Upgrading a conventional hydrological information system—an Indian example

H. CHOWDHARYHydrology Project, CSMRS Building, Hauz Khas, New Delhi 110016, Indiae-mail: [email protected]

S. K. JAINNational Institute of Hydrology, Roorkee 247667, India

H. J. M. OGINKHydrology Project, CSMRS Building, Hauz Khas, New Delhi 110016, India

Abstract The existing hydrological information systems in many countries lack reliability, accessibility and timeliness. The main causes are substandard observation practices, manual processing, the wide gap between the tools available and those employed, and the involvement of many agencies, often lacking integration. A comprehensive computerized hydrological–geographic database is the key to efficient water management. An attempt to improve the existing systems in nine peninsular states of India is underway through the Hydrology Project. The prime objective of the Hydrology Project is to standardize data collection and processing and develop a hydrological information system (HIS). Infrastructure development, maintenance, and training of personnel are emphasized to ensure sustainability. The key features of HIS and experiences from revitalizing the existing system over a region of about 1.7 million km2 are highlighted.Key words hydrological information system; hydrological data; data processing; India


The development of an information modelling system for regional water resource assessments

DENIS HUGHESInstitute for Water Research, Rhodes University, Grahamstown 6140, South Africae-mail: [email protected]

Abstract The paper outlines the development of a software package that integrates spatial and time series information in a flexible framework that allows for a wide variety of data storage, retrieval, analysis, display and modelling options. In the context of regional water resource assessments, the advantage of such a tool is that a wide variety of information and data analysis methods can be brought together into a single package. This allows a wide range of users to make use of the same information storage system and apply consistent methods to water resource assessments, permitting a greater degree of commonality of approach within the region.Key words databases; software; modelling; water resources


Detection of intensification of the global water cycle: the potential role of FRIEND

Alan d. ZieglER, Justin Sheffield, Eric F. WoodEnvironmental Engineering & Water Resources, Princeton University, Princeton, New Jersey 08544, USAe-mail: [email protected]

Bart Nijssen, Edwin P. Maurer & Dennis p. LettenmaierCivil Engineering, University of Washington, Seattle, Washington 98195, USA

Abstract Diagnostic studies of 14-year, 2 × 2°, Variable Infiltration Capacity (VIC) model off-line simulations of the global terrestrial water budget suggest that, given the annual variability in the major components of continental hydrological cycles (precipitation, evaporation, and runoff), several decades to perhaps centuries of measurements may be needed to detect with high confidence the intensification predicted by recent global climate model (GCM) studies simulating plausible global warming scenarios. Furthermore, these measurements may need to originate from a wider geographic expanse than is currently investigated within large-scale hydrological assessment programmes, such as the Global Energy and Water Experiment (GEWEX). Smaller, geographically dispersed basins, including many of those participating in the International Flow Regimes from International Experimental and Network Data (FRIEND) programme, could therefore play important roles in detection of an intensification in the global water cycle.Key words climate change/variability; trend detection; hydrological cycle acceleration


Statistical analysis of at-site extreme rainfall processes in Peninsular Malaysia

ZALINA MOHD DAUD, AMIR HASHIM MOHD KASSIMFaculty of Science, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysiae-mail: [email protected]

MOHD NOR MOHD DESAHumid Tropics Centre, Department of Irrigation and Drainage, 68000 Ampang, Kuala Lumpur, Malaysia

VAN-THANH-VAN NGUYENDepartment of Civil Engineering and Applied Mechanics, McGill University, 817 Sherbrooke Street West, Montreal, Quebec H3A 2K6, Canada

Abstract Quantitative goodness of fit tests were done to determine the probability distribution most appropriate for describing annual maximum rainfall series in Peninsular Malaysia. Parameter estimation was based on the L-moment method. Bootstrap resampling was done to investigate the predictive ability of each distribution. The combined results obtained suggested the generalized extreme value (GEV) as the most appropriate distribution. Intensity–duration frequency curves based on GEV were constructed and comparisons were made to the existing Gumbel based curves (generally employed in practise in Malaysia). A regionalization study involving clustering of homogeneous sites and quantile estimation of ungauged sites was also investigated. The index-flood and station-year methods were compared with results in favour of the station-year method.Key words extreme rainfall; probability distribution; Peninsular Malaysia; L-moment; PPCC test; bootstrap resampling; regionalization; index-flood method; station-year method; jack-knife procedure


Climatic and anthropogenic impacts on the flow regime of the Nakambe River in Burkina Faso

G. MAHE, A. DRAY, J. E. PATUREL, A. CRESInstitut de Recherche pour le Développement (IRD), 01 BP 182, Ouagadougou, Burkina Fasoe-mail: [email protected]

F. KONE, M. MANGA, F. N. CRES, J. DJOUKAM, A. MAIGA, M. OUEDRAOGOEIER, 03 BP 7023, Ouagadougou, Burkina Faso

D. CONWAYSchool of Development Studies, University of East Anglia, Norwich NR4 7TJ, UK

E. SERVATInstitut de Recherche pour le Développement, BP 5045, F-34032 Montpellier Cedex, France

Abstract The annual hydrological regime of the Nakambe River shows substantial changes during the period 1955 to 1998 with a shift occurring around 1970. From 1970 to the mid 1990s, despite a reduction in rainfall and an increase in the number of dams, runoff increased, including maximum daily discharges, and a delay of several weeks in the timing of peak flows occurred. To assess the impact of land-use change on soil water holding capacity (WHC) during this period we compare the results of two monthly hydrological models using several different rainfall, potential evapotranspiration (PE) and WHC data sets. Soil WHC values are modified over time using historical maps of land use, and compared with a constant value for WHC over time. There is a moderate improvement in flow simulation using the varying values of soil WHC.Key words land use; soil water holding capacity; hydrological modelling; Sahel; Burkina Faso


Analysis of basin response resulting from climate change and mitigation measures

Erik P. QUERNERAlterra, PO Box 47, 6700 AA Wageningen, The Netherlandse-mail: [email protected]

Abstract The very wet conditions of recent years in Europe have made it clear that measures will have to be taken in this century to prevent flooding. Therefore this study analyses the changes in peak discharge resulting from climate change and the efficiency of mitigation measures. A scenario study was set up, using the SIMPRO model, to simulate shallow groundwater flow locally and water flow in a network of water courses regionally. The climate scenarios represented the period 2050–2100, which is expected to be warmer and wetter. Three mitigation measures to reduce these peak flows were studied. The discharge analysis was done for five regions of The Netherlands, ranging in size from 25 to 142 km2. The results suggest that climate change would increase peak discharges by 10–30%. Of the three mitigation measures analysed, reducing peak discharges by gates or culverts was found to be very effective; it could cancel out the effect of climate change.Key words drainage basin; climate change; mitigation measure; rainfall; evapotranspiration; groundwater; surface water; modelling; scenario


Hydrological drought studies in the wide context of climate variability

LADISLAV KAŠPÁREKT. G. Masaryk Water Research Institute, Podbabská 30, 160-62 Prague 6, Czech Republice-mail: [email protected]

OLDŘICH NOVICKÝMinistry of the Environment, Vršovická 65, 100-10 Prague 10, Czech Republic

Abstract The aim of the study was to contribute to a better understanding of spatial and temporal variability in flow and drought characteristics in Europe. The results showed that during the nineteenth and twentieth centuries the large European rivers analysed exhibited similar flow patterns. The highest long-term flow changes were detected in the nineteenth century, a period when climate and flows were not significantly affected by human activities. It was demonstrated that long-term climate variability (mainly variability in precipitation) was the main causal factor of the long-term variability in the runoff, while the role of changes in land use was substantially less important. Similarities were also detected in long-term time patterns (twentieth century) of the deficit volumes derived for six river gauging stations selected from a small area located in the eastern part of the Elbe basin. These similarities were, however, accompanied by high short-term temporal and spatial variability in the drought characteristics.Key words hydrological drought; low flows; long European runoff series; drought characteristics; drought severity; drought duration; deficit volume


Scenarios assessing the influence of climate variability on drought in Europe

KERSTIN STAHL, BIRGIT HASSLER & SIEGFRIED DEMUTHInstitute of Hydrology, University of Freiburg, Fahnenbergplatz, D-79089 Freiburg, Germanye-mail: [email protected]

Abstract Regional drought events defined by streamflow deficiencies derived from more than 600 streamflow data records from the European Water Archive (EWA) were assessed in this study. Through logistic regression, the events were linked to the occurrence of the European “Grosswetterlagen”, atmospheric circulation patterns (CPs), which describe the synoptic meteorological situation. Two scenarios of changed CP frequencies were generated to represent changed climatic conditions. The non-significant response to a scenario motivated by recently observed trends in the CP frequencies indicates no aggravation of the drought risk for the four selected regions in the UK, Norway and Germany. Seasonal scenarios of changed high pressure and low pressure patterns suggest a strong influence of winter recharge on drought conditions for the southeast of the UK. The results indicate the potential of the method for the assessment of the impact of climate change on drought in Europe.Key words streamflow; drought; Europe; circulation patterns; logistic regression; scenarios; climate variability


Temporal variability of recharge as an indicator for natural groundwater droughts in two climatically contrasting basins

HENNY A. J. VAN LANEN & ELISABETH PETERSSub-department of Water Resources, Wageningen University, Nieuwe Kanaal 11, 6709 PA Wageningen, The Netherlandse-mail: [email protected]

Abstract Recharge has been simulated in two European basins, i.e. Upper-Guadiana, Spain (semiarid) and Noor, The Netherlands (temperate, humid). Reservoir theory (Sequent Peak Algorithm) is used to derive natural groundwater droughts from long recharge time series. Such droughts are controlled by weather conditions and not by human activities. They are obviously more severe and last longer in semiarid Europe. The severest drought in the Upper-Guadiana lasted three times longer than in the Noor. Moreover, the droughts do not coincide in both climatic regions. In the Noor basin natural droughts agree reasonably with the groundwater droughts derived from groundwater hydrographs due to the low impact of human activities. In the Upper-Guadiana groundwater abstraction leads to substantial differences between natural groundwater droughts and droughts derived from groundwater levels. Simulation modelling (recharge, groundwater hydrographs) can improve understanding of the impact of weather and human activities, including mitigation measures on droughts.Key words drought; groundwater; recharge; Sequent Peak Algorithm; temporal variability; modelling; Guadiana (Spain); Noor (The Netherlands)


Impact of climate change on flooding in the UK: a methodology for estimating uncertainty

Christel Prudhomme, Dörte Jakob & Cecilia SvenssonCentre for Ecology and Hydrology, Wallingford, Oxfordshire OX10 8BB, UKe-mail: [email protected]

Abstract The paper presents a rigorous methodology to assess the impact of climate change and its uncertainties on the flood regime. Uncertainties in global climate modelling are accounted for through a range of climate change scenarios derived from several general climate models using simple downscaling techniques. The hydrological modelling is undertaken in several steps. First, a conceptual rainfall–runoff model is calibrated using measured climatic and hydrological series, representative of the current climatic conditions. Secondly, the baseline climatic series are perturbed according to the climate change scenarios and runoff series simulated. Finally, for each simulated series, the flood regime is assessed using standard flood frequency procedures. The methodology is applied to a case-study basin in the south of England for the 2050s time horizon. Results show an increase in the magnitude and frequency of flood events of low return periods, these changes becoming less significant for rarer events.

Key words climate change impact; flooding; UK; uncertainty; general climate models (GCMs); continuous flow simulation; flood frequency analysis


Modelling of flood flows in Rufiji River basin, Tanzania

SIMON H. MKHANDI, RAJ KACHROO & FELIX MTALOWater Resources Engineering Programme, University of Dar es Salaam, PO Box 35131, Dar es Salaam, Tanzaniae-mail: [email protected]

Abstract A simulation procedure applied to select a suitable statistical procedure to model flood flows in Rufiji River basin in Tanzania is presented. In this paper, a flood frequency procedure refers to the combination of a probability distribution with a suitable method of parameter estimation. A predictive ability test based on bias between observed and predicted flows is used to select the suitable procedure. Based on the results of the simulation, the most suitable statistical frequency procedures for modelling flood flows for the homogeneous regions of Rufiji basin seem to be log-Pearson type 3/method of moments (LP3/MOM) and Pearson type 3/method of probability weighted moments (P3/PWM). The two procedures gave the lowest bias values for different return periods and sample sizes considered in the study. The study is based on the data from 42 sites in the basin.Key words Rufiji River; frequency analysis, homogeneous regions; regional homogeneity; graphical test; parent distribution; quantile estimate; statistical distribution


Prédétermination régionale des débits de crue. Cas de la zone méditerranéenne française

JACQUES LAVABRE, NATHALIE FOLTON, CATHERINE FouchierCEMAGREF Aix-en-Provence, BP 31, F-13612 Aix-en-Provence Cedex 1, Francee-mail: [email protected]

A. FAURE-SOULETCETE Méditerranée, BP 37000, F-13791 Aix-en-Provence Cedex 3, France

Résumé L’objectif de l’étude est la connaissance régionale des débits de crue de différentes durées et de différentes fréquences. La méthodologie utilisée associe un simulateur de pluies horaires et une modélisation simple de la pluie en débit. Les quantiles de débits se déduisent directement des distributions de fréquence des longues chroniques de débit qui peuvent être simulées. Cette information est pixélisée au km2. L’estimation des quantiles de débits pour un bassin versant de la zone d’étude nécessite l’agglomération de l’information ponctuelle, ce qui nous a conduit à introduire la notion de fonction de transfert statistique (FTS).Mots clefs pluie; débit; modélisation; fonction de transfert; régionalisationKey words rainfall; runoff; rainfall stochastic model, rainfall–runoff model; statistical transfer function; regionalization


Flood-plain inundation based on coupled hydraulic and GIS models

URSZULA SOCZYNSKA†, ARTUR MAGNUSZEWSKI, BARBARA NOWICKADepartment of Hydrology, Warsaw University, Krakowskie Przedmiescie 30, 00-927 Warsaw, Polande-mail: [email protected]

JAN JELOWICKIDepartment of Mathematics, Wrocław University of Agriculture, Grunwaldzka 51, 51-357 Wrocław, Poland

Abstract The one-dimensional hydrodynamic model SiReN has been used for flood routing calculations for the small mountain Skora River (278 km2) in the Sudety region of Poland. Results of the model have been displayed using a digital terrain model to show the range of potential inundation of the flood plain. This type of combined modelling can by used to visualize floods of given recurrence interval and their propagation under unsteady flow conditions. Simulation of 10, 1, and 0.1% probability floods for a 15.2-km-long reach of the Skora River valley has been performed using a digital terrain model. The results obtained are useful for the design of hydraulic structures, proper spatial planning and flood mitigation procedures.Key words Skora River; flood routing model; digital terrain model (DTM); geographical information system (GIS); recurrence interval

† The Editors regret to announce the death of Prof. Urszula Soczynska on 17 October 2001.


Estimating design floods for small earth dams in Malawi

M. P. MCCartneyCentre for Ecology and Hydrology, Wallingford, Oxfordshire OX10 8BB, UKe-mail: [email protected]

A. B. ChirwaMinistry of Water Development, Private Bag 390, Capital City, Lilongwe 3, Malawi

H. A. HOUGHTON-CARRCentre for Ecology and Hydrology, Wallingford, Oxfordshire OX10 8BB, UK

Abstract Small earth dams are a common device for water harvesting and storage throughout the rural areas of Malawi and the rest of southern Africa. As a source of water during dry periods, they are a vital resource for many rural communities. Estimates of flood magnitudes and associated return periods are required for the safe design of dams. This paper summarizes guidelines for deciding the return period of design floods and for estimating their magnitude at ungauged sites by statistical techniques. These guidelines are available to those involved in the design and rehabilitation of small earth dams in Malawi and elsewhere in southern Africa.Key words small earth dams; rainfall–runoff relationships; design flood; spillway design


Conséquences de la sécheresse observée depuis le début des années 1970 en Afrique de l’Ouest et centrale: normes météorologiques et hydrologiques

MAHAMAN OUEDRAOGO, JEAN-EMMANUEL PATUREL, GIL MAHEInstitut de Recherche pour le Développement, 01 BP 182, Ouagadougou 01, Burkina Fasoe-mail: [email protected]

ERIC SERVATInstitut de Recherche pour le Développement, BP 5045, F-34032 Montpellier Cedex, France

Résumé Ces travaux s’inscrivent dans le cadre du projet FRIEND Afrique de l’Ouest et centrale. Ils concernent le Burkina Faso, la Côte d’ivoire et le Mali et veulent apporter une contribution au débat sur la révision des normes hydrologiques et météorologiques. Plusieurs auteurs ont souligné le besoin pressant de la révision des normes hydrologiques et météorologiques. En effet, les déficits pluviométrique et hydrométrique de ces 30 dernières années soulèvent le problème de la période de référence à considérer pour les estimations des caractéristiques hydrologiques. L’hypothèse qui sous-tend ces estimations est une stabilité du climat alors que la prise en compte ou non des données des années récentes sur les calculs de ces caractéristiques ne peut conduire qu’à des résultats très différents et à de graves répercussions.Mots clefs norme météorologique; norme hydrologique; variabilité climatique; Afrique de l’Ouest et centraleKey words meteorological normals; hydrological normals; climatic variability; West and central Africa


Management of drought risk in the Sudano-Sahelian region of Nigeria

OLUSEGUN ADEAGADepartment of Geography, University of Lagos, Akoka-Yaba, Lagos State, Nigeriae-mail: [email protected]

Abstract Drought is a prolonged absence or marked deficiency of precipitation. One major consequence of this abnormality has always been shortage of water for man and his activities. This is usually evidenced by a reduction of streamflow and soil moisture and lower lake and groundwater levels. Thus, drought occurrence has always resulted in an enormous loss of lives and properties as well as disruption of economic and social structures with a lot of institutional consequences most especially in the developing world. Rational water management therefore requires an in-depth study of drought severity, occurrence and duration among others, in order to provide precise and accurate scenarios for decision-making processes on drought management and preparedness schemes.Key words hydrological risk; Sudano-Sahelian; drought management; trend analysis; normalized departure


Changes in the hydrological response of two Sicilian basins affected by fire

GIUSEPPE ARONICADipartimento di Costruzioni e Tecnologie Avanzate, Università di Messina, Salita Sperone 31, I-98166 S. Agata, Messina, Italye-mail: [email protected]

ANGELA CANDELA & MARIO SANTORODipartimento di Ingegneria Idraulica e Applicazioni Ambientali, Università di Palermo, Viale delle Scienze-Parco d’Orleans, I-90128 Palermo, Italy

Abstract The aim of this paper is to detect possible changes in the hydrological response of two Sicilian basins with different extents of burnt area. Efforts were made to detect changes in the annual, monthly and daily runoff and in the annual flood peaks. On an annual and monthly basis, no changes in peak discharge and runoff were found for the basin with a smaller burnt area, while for the basin with a larger burnt area a significant increase in the value of the runoff coefficient was detected. However for both basins daily runoff values did not show any change based on a comparison of the parameters of the derived instantaneous unit hydrograph. Finally the flood frequency curves, derived by fitting the two-parameter lognormal distribution to peak discharges measured at the basin outlet show lower values of peak discharges for the period encompassing data for the year after the fire.Key words forest fire; hydrological response; rainfall–runoff; semiarid areas; Sicily


Regionalization for one to seven day design rainfall estimation in South Africa

JEFFREY SMITHERS & ROLAND SCHULZESchool of Bioresources Engineering and Environmental Hydrology, University of Natal, Private Bag X01, Scottsville 3209, South Africae-mail: [email protected]

Abstract Accurate estimates of design rainfall are essential input in the design of hydraulic structures. Design rainfalls in South Africa for durations of 1 day and longer were last computed using a single station approach in the early 1980s. Currently longer periods of data are now available for analysis. Moreover, techniques for estimating design values using a regional approach, which generally result in more reliable and robust design values than traditional single-site approaches and enables the estimation of design values at ungauged sites, have now become accepted practice internationally. In this paper the results of applying a regionalized index storm approach based on L-moments to estimate 1–7 day duration design rainfalls in South Africa is presented.

Key words design rainfall; regional L-moment algorithm; extreme storms; South Africa


Methods for identifying and monitoring river flow drought in southern Africa

JEREMY MEIGH, EMMA TATE & MATTHEW MCCARTNEYCentre for Ecology and Hydrology, Wallingford, Oxfordshire OX10 8BB, UKe-mail: [email protected]

Abstract The importance of the water resources aspects of drought is being increasingly recognized. In this paper, improved methods for the identification of river flow droughts in southern Africa are investigated, and tools to assist in the realistic determination of the severity of droughts and to provide effective means of monitoring droughts as they develop, are considered. Because of the complexities of drought behaviour over large regions, a combination of different approaches is useful. The techniques have been combined in a software package to provide rapid assessments. Such operational tools will be increasingly useful for managing hydrological risk as greater volumes of near real-time flow data become available in the future.Key words hydrological drought; water resources; low flow frequencies; run–sum analysis; runoff accumulation analysis; ranking of flows; southern Africa


Towards rainfall–runoff models that do not need calibration to flow data

Richard Ibbitt & Ross WoodsNational Institute of Water and Atmospheric Research, PO Box 8602, Christchurch, New Zealande-mail: [email protected]

Abstract A spatially-distributed hydrological model based on Topmodel is used, without calibration, to simulate flows and soil moisture variation at the Mahurangi basin, New Zealand. Inconsistencies caused by measuring the saturated hydraulic conductivity of the soil at one spatial scale and estimating the distribution of the topographic index ln(a/tanβ) at a different scale, are discussed. The results indicate that estimates of hourly flows using an uncalibrated model are practical, but that less certainty can be placed on the simulated soil moisture values.Key words Topmodel; soil moisture


Redéfinition des fonctions de production des modèles globaux de relation pluie–débit en milieu semi-aride africain

SANDRA ARDOIN, ALAIN DEZETTER, ERIC SERVAT & CLAUDE BOCQUILLONInstitut de Recherche pour le Développement, UMR Hydrosciences, BP 5045, F-34032 Montpellier Cedex 1, Francee-mail: [email protected]

Résumé En zone semi-aride, l’évapotranspiration est un processus important du cycle hydrologique. Sa prise en compte est, donc, essentielle dans le cadre de la modélisation pluie–débit. Afin de valider une approche permettant le calcul de l’évapotranspiration réelle, quatre fonctions de productions sont testées en privilégiant la réserve en eau du sol. Ces tests sont réalisés au moyen du modèle conceptuel GR3J du CEMAGREF, sur treize bassins versants du nord Côte d’Ivoire. Les résultats obtenus soulignent l’intérêt de cette démarche: les calages effectués sont de bonne qualité et les hydrogrammes sont correctement reconstitués. L’utilisation de fonctions de production, en référence à la quantité d’eau disponible dans le sol, donne des résultats qui sont au moins du même niveau que les formulations utilisées classiquement.Mots clefs Côte d’Ivoire; évapotranspiration; modélisation pluie–débit; fonctions de productionKey words Ivory Coast; evapotranspiration; rainfall–runoff modelling; loss functions


On-line short-term streamflow forecasting using neural networks

MOHD YUSOFF MASHORCentre for ELectronic Intelligent System (CELIS), School of Electrical and Electronic Engineering, University Sains Malaysia, 14300 Nibong Tebal, Pinang, Malaysiae-mail: [email protected]

Abstract Previous studies showed that a hybrid multi-layered perceptron network (HMLP) coupled with a modified recursive prediction error (MRPE) training algorithm has a very good prediction performance. The network has a compact structure and can be trained rapidly. HMLP network does not require multiple training epochs. Based on these promising properties of HMLP and MRPE, the current study investigates the capability of the network to perform on-line short-term streamflow forecasting. A portable on-line short-term streamflow system will be built, which includes a flow sensor to measure streamflow and a HMLP network to model and at the same time forecast the streamflow. The simulation study showed that the system starts to give good forecasting results after 150 training samples for 3-h ahead and good 24-h ahead after 300 samples. These results suggest that the system is suitable for short-term on-line forecasting.Key words neural network; HMLP network; MRPE algorithm; streamflow forecasting; on-line modelling; short-term forecasting; Pari River; Malaysia


Frequency analysis models for long hydrological time series in Southeast Asia and the Pacific region

JOESRON LOEBISResearch Institute for Water Resources Development, Jl. Ir. H. Juanda 193, Bandung 40135, Indonesiae-mail: [email protected]

Abstract In 1993 the IHP Regional Steering Committee for Southeast Asia and the Pacific was established with 13 countries to carry out IHP-V regional projects in comparative hydrology and water resources. The Catalogue of Rivers for Southeast Asia and the Pacific has been published and the Asian Pacific FRIEND programme was established in 1996, of which the Working Group for Frequency Analysis Models forms a part. By using the long hydrological time series data provided in the Asian Pacific Water Archive, some standard frequency analysis models are applied to the regional hydrological extreme value data sets and their applicability assessed. Different distribution characteristics, suitable for each river basin or region, could be attributed to the regional nature of flooding. The results are expected to contribute to the standard methods for flood forecasting used for water resources development and management in Southeast Asia and the Pacific region.Key words Asian Pacific river basin; frequency analysis; data sets; Gumbel method; extreme value


Modélisation débit–durée–fréquence appliquée aux grands bassins versants du Burkina Faso

AMADOU LAMINE MAR, PHILIPPE GINESTEUMR Hydrosciences Montpellier et Ecole Inter-Etats d’Ingénieurs de l’Equipement Rural, 03 BP 7023, Ouagadougou 03, Burkina Fasoe-mail: [email protected]

HAMATTAN MOHAMED, ALY TOUNKARAEcole Inter-Etats d’Ingénieurs de l’Equipement Rural, 03 BP 7023, Ouagadougou 03, Burkina Faso

LUDOVIC TAPSOBADirection de l’Inventaire des Ressources Hydrauliques, 03 BP 7025, Ouagadougou 03, Burkina Faso

PIERRE JAVELLE

CEMAGREF Lyon, Division Hydrologie–Hydraulique, 3 bis Quai Chauveau, F-69336 Lyon Cedex 09, France

Résumé Les modèles débit–durée–fréquence (QdF), développés au CEMAGREF de Lyon, donnent une synthèse du régime hydrologique et constituent un outil bien adapté à la gestion des ressources en eau. Dix huit stations hydrométriques du Burkina Faso dont les superficies de bassin versant sont supérieures à 800 km2 ont été choisies pour ce faire; ces stations comportant les plus longues séries de débits journaliers avec malgré tout des taux de lacunes élevés. Les hypothèses du modèle que sont l’invariance d’échelle, l’ajustement à la loi exponentielle et la forme hyperbolique des quantiles pour chaque durée ont été bien vérifiées pour huit stations où la dynamique des crues semble être directement liée aux précipitations et sans influence d’aucun ouvrage. La taille du bassin versant n’a pas été un facteur discriminant sauf pour le choix des durées significativement différentes.Mots clefs courbes débit–durée–fréquence (QdF); échantillonnage par valeurs supérieures à un seuil; logiciel XSD; crues; bassin versant; Burkina FasoKey words flow–duration–frequency curves; over-threshold sampling; XSD software; floods; basin; Burkina Faso


Coupling limited area models with distributed hydrological models for flood forecasting: the Toce basin case study

Nicola Montaldo, Vania Toninelli, Marco Mancini & Renzo RossoDepartment of Hydraulic, Environmental and Surveying Engineering, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20121 Milan, Italye-mail: [email protected]

Abstract The combined use of meteorological limited area models (LAMs) and hydrological models in basins ranging from 101 to 103 km2 can be a powerful tool to extend the lead times of flood warning systems. The Alpine Toce basin (area 1534 km2) is presented as a case study. LAM predictions from the BOLAM, Meso-nh, SM and MC2 models are available for three recent floods, and are used as input to a distributed hydrological model. For each of the three flood events we present a comparison of the observed and simulated hydrographs, with separate simulations provided from (a) using LAM rainfall inputs, and (b) observed rainfall records. Analysis of the results demonstrates the reliability of the coupled model approach and highlights the importance of an accurate representation of the basin topography in the coupled LAM–hydrological model. The application of this procedure is extended to basin sections draining areas between 11 and 1534 km2. The results indicated a basin scale lower limit of about 300 km2, below which the simulated hydrographs obtained from LAMs do not provide reliable results.Key words flood warning; hydrological models; meteorological models; basin scale; Toce basin, Italy


Development of flood boundary maps of urban areas using HEC-RAS software

K. BRYCH, F. DITTRT & V. ELIAS†

Institute of Hydrodynamics, Academy of Sciences of the Czech Republic, Pod Patankou 5, 166-12 Prague 6, Czech Republice-mail: [email protected]

Abstract Flood hazard maps of urban areas in the Orlice Valley (Czech Republic) were developed using HEC-RAS software. Extreme floods were considered to calibrate the hydraulic model of the Orlice River system. The calculated boundary of the flood extension area was fitted to the observed boundary by optimizing the Manning’s roughness coefficient. These parameters were then used to compile a flood boundary map corresponding to a 100-year flood. A digital terrain model (DTM) is a pre-requisite for map compilation in the ArcView environment. The ZABAGED/1 state atlas on a 1:10 000 scale, available for selected regions of the Czech Republic, is usually being used as the DTM. This system contains land-surface elevation data in a vector format. Taking into account the limited altimetric resolution of ZABAGED, we used geographic maps on a 1:1000 scale derived from regional aerial photography.

Key words Orlice River basin; Czech Republic; flood plain inundation; flood hazard map; 100-year flood; HEC-RAS model

† The Editors regret to announce the death of Dr Vaclav Elias.


Regional analysis of the generation of extreme floods

STEFAN UHLENBROOK, Andreas Steinbrich, Dörthe Tetzlaff & Chris LeibundgutUniversity of Freiburg, Institute of Hydrology, Fahnenbergplatz, D-79098 Freiburg, Germanye-mail: [email protected]

Abstract The significance of meteorological input and the physiographic basin properties for runoff generation during extreme floods (recurrence intervals of greater than 10 years) was investigated for 29 mesoscale basins in southwest Germany. Precipitation was found to be most significant for causing floods whereas digital data available on physiographic features were less significant. A distinct seasonality in the occurrence of extreme floods and a less pronounced seasonality of precipitation events were found. In addition, different recurrence intervals for precipitation and flood events were calculated for different seasons. This finding should be considered in applied hydrological studies for a reliable flood assessment.Key words extreme floods; extreme precipitation; seasonality; correlation analysis; Baden-Württemberg


GIS-based development of regional low-flow analysis for southern Taiwan

YU PAO-SHAN & SHIH MIN-LUENDepartment of Hydraulic and Ocean Engineering, National Cheng Kung University, 1 Ta-Hsueh Road, Tainan 70101, Taiwane-mail: [email protected]

Abstract This study aims primarily to develop a regional low-flow duration curve that can be used to acquire low-flow information for any ungauged site in southern Taiwan. This study incorporated a visual interface and a geographical information system (GIS) in a regional analysis to provide a user-friendly interface. The basin area, mean slope and hydrogeological information are then abstracted from the database and substituted into the regional low-flow duration curve, and the low-flow information at the ungauged basin can be rapidly and intuitively presented.Key words low flow; ungauged basin; cluster analysis; geographical information system (GIS); southern Taiwan


Regionalization of low-flow frequency estimates for rivers in northwest Bangladesh

M. FAZLUL BARIDepartment of Water Resources Engineering, Bangladesh University of Engineering and Technology (BUET), Ramna, Dhaka 1000, Bangladeshe-mail: [email protected]

SABINA SADEKSWMC, House 476, Road 32, New DOHS, Mahakhali, Dhaka 1206, Bangladesh

Abstract Development of models of probabilistic phenomena such as low flows is often hindered by short record lengths. At-site estimates of parameters and low-flow quantiles may not be so reliable. In flood frequency analysis, one approach to overcome this difficulty is regional frequency analysis. The same general approach is applied here in the case of low-flow estimation. Daily streamflow data from 13 gauging stations in northwest Bangladesh are used. Weibull, also known as extreme type 3 for minimum, and log-Pearson type 3 distributions

are found to be suitable for modelling low flows of the rivers in this region. The shape parameters of the distributions are estimated on a regional basis. Low-flow quantiles estimated by regional and at-site frequency analysis are compared.Key words low flow; regional analysis; probability distributions; log-Pearson type 3; Weibull; parameter estimation; northwest Bangladesh


Groundwater runoff separation—test of applicability of a simple separation method under varying natural conditions

LADISLAV HOLKOInstitute of Hydrology, Slovak Academy of Sciences, Ondrasovecka 16, 031-05 Liptovsky Mikulas, Slovakiae-mail: [email protected]

ANDREAS HERRMANNInstitute of Geography and Geoecology, Technical University Braunschweig, Langer Kamp 19c, D-38106 Braunschweig, Germany

STEFAN UHLENBROOKUniversity of Freiburg, Institute of Hydrology, Fahnenbergplatz, D-79098 Freiburg, Germany

LAURENT PFISTERCREBS—Cellule de Recherche en Environnement et Biotechnologies, CRP-Gabriel Lippmann, 162a Avenue de la Faïencerie, L-1511 Luxembourg, Luxembourg

ERIK P. QUERNERAlterra, PO Box 47, 6700 AA Wageningen, The Netherlands

Abstract Groundwater runoff was computed for five European basins using the method based on the relationship between the groundwater table and stream discharge. The results highlight the active role of groundwater in basin runoff formation. At least 49% of total basin runoff was contributed by groundwater on average and the groundwater contributions were high also during flood events. Evaluation of separated groundwater runoff using knowledge gained from experimental hydrological research in the basins including tracer studies and hydrometric studies indicated that the results are reasonable.Key words groundwater runoff; hydrograph separation; groundwater table–stream discharge relationship


Meteorological droughts focused on a pan-European context

MARIA JOÃO SANTOS, RAQUEL VERÍSSIMO, SÓNIA FERNANDES, MARCO ORLANDO & RUI RODRIGUESPortuguese Institute for Water (INAG), Av. Almirante Gago Coutinho 30, 1049–066 Lisbon, Portugale-mail: [email protected]

Abstract A regional drought model describing annual precipitation in a large part of Europe has been applied. The regional model considers 12 regions in Europe: Alps, Atlantic Iberia, central Europe, central Iberia, Crete, Great Britain, Ireland, Italy, Scandinavia, south Balkans, western France and western Mediterranean. The regional model fulfils several objectives that are not satisfactory dealt with the commonly-used widespread methodologies based on the concept of point drought. Additionally this method obtains recurrence intervals for regional drought by extreme-value analysis. The regional resolution and representativeness of the model estimates allows its transferability to different climatic environments as well as different hydrometeorological variables, making it a powerful tool for hydrological risk management.Key words regional drought; statistical model; return period; meteorological drought; annual precipitation; Europe; definition of regions


Handling non-extreme events in extreme value modelling of streamflow droughts

HEGE HISDALNorwegian Water Resources and Energy Directorate, Box 5091 Majorstua, N-0301 Oslo, Norwaye-mail: [email protected]

LENA M. TALLAKSENDepartment of Geophysics, University of Oslo, Box 1022 Blindern, N-0315 Oslo, Norway

ARNOLDO FRIGESSINorwegian Computing Center, Box 114 Blindern, N-0314 Oslo, Norway

Abstract In this study the truncation level approach was adopted to derive partial duration series of drought deficit volumes. The 10- and 100-year drought events including their standard errors were estimated for 12 daily streamflow series from around the world, representing a wide range of hydrological regimes. According to extreme value theory the generalized Pareto distribution was applied as the limit distribution to excesses over a high threshold. A special problem often arises due to the presence of a few large and many minor drought events. It is suggested how extreme value tools, the mean excess plot and the “horror” plot (plot of the shape parameter as a function of threshold), earlier not applied in drought studies, can be helpful in improving the fit. It was concluded that the “horror” plot provided the best tool for removing minor droughts disturbing the extreme value modelling with a minimum of subjectivity. It is therefore recommended that it should assist generalized Pareto modelling of partial duration series of droughts.Key words droughts; partial duration series; extreme value modelling; generalized Pareto distribution; global data set


Modelling summer and winter droughts as a basis for estimating river low flows

GREGOR LAAHADepartment of Applied Statistics, University of Agricultural Sciences (BOKU), Gregor Mendel Strasse 33, A-1180 Vienna, Austriae-mail: [email protected]

Abstract An approach is presented towards modelling low flow characteristics from basin characteristics based on seasonalities which, ultimately, can be used for estimating design values for ungauged sites. The main idea behind this approach is that summer and winter droughts are related to important differences in underlying physical processes. Consistent modelling of low flows therefore should be based on a separation into groups with similar seasonality. Different methods for detecting regional seasonality patterns have been applied to data from 57 monitored basins in Upper Austria. Results indicate a clear spatial separation between stations with typical summer and winter seasonality depending on altitude. For modelling nonlinear relationships, interactions and discontinuous patterns, regression tree modelling is proposed and appears to be more appropriate then multiple regression.Key words low flow; drought; seasonality; regionalization; regression tree; multiple regression; cluster analysis


Noise level estimation of chaotic hydrological time series

A. W. JAYAWARDENADepartment of Civil Engineering, The University of Hong Kong, Hong Kong, Chinae-mail: [email protected]

XU PENCHANGAcademy of Mathematics and System Sciences, Chinese Academy of Sciences, Beijing, China

BELLIE SIVAKUMARDepartment of Land, Air and Water Resources, University of California, Davis, California 95616, USA

Abstract A new method of estimating the noise level present in a chaotic hydrological time series is presented. The effectiveness of the method is first demonstrated using two artificial chaotic time series, i.e. the Henon map and the Lorenz equation, whose dynamic characteristics are known a priori, and then tested on two real hydrological time series: daily streamflow series observed in the Chao Phraya River basin in Thailand (raw data), and the same data “cleaned” by the method of Schreiber (1993a). Different levels of noise are added to the artificial chaotic time series in order to demonstrate the effectiveness of the method. A comparison of the results obtained using the proposed method and the method by Schreiber (1993a) clearly indicate a much better performance of the proposed method.Key words noise; noise level estimation; noise reduction; chaotic hydrological series; artificial chaotic series


Treaty on sharing the Ganges waters: a milestone towards regional cooperation for development and management of water resources

Md. AZIZUL HAQUEJoint Rivers Commission, House 13, Road 4, Dhanmondi R.A., Dhaka 1205, Bangladeshe-mail: [email protected]

Abstract Bangladesh, the lowest riparian country of the Ganges–Brahmaputra–Meghna (GBM) region, faces an acute shortage of water during the dry season while there is abundant water during the monsoon. Identical conditions prevail in the other GBM countries. There is immense potential for improving the economical and social conditions in this region by utilizing the huge water resources through regional cooperation. Progress in long-term regional cooperation has been impeded by mutual mistrust, lack of goodwill and differences in perception. The signing of the Ganges Waters Sharing Treaty has helped tremendously in changing the atmosphere for cooperation. This treaty, a milestone towards regional cooperation, offered the opportunity for collaboration in water-based development endeavours which will undoubtedly improve the prosperity of the people living in the region.Key words Bangladesh; Ganges–Brahmaputra–Meghna region; potential; water resources; regional cooperation; treaty; milestone; prosperity


Sustainable management of water resources in an agriculturally developed region of the Indo-Gangetic ecosystem, India

R. B. SINGHDepartment of Geography, Delhi School of Economics, University of Delhi, Delhi 110007, Indiae-mail: [email protected]

Abstract With a geographical area of 329 106 ha, India is endowed with vast water resources. It is predominantly an agriculture-based country where two-thirds of the population still depends on agriculture. Water resources development has been playing a dominant role in agricultural development and achieving self-reliance in food production. Indiscreet use of water for irrigation adversely affects growth, yield and quality of crops together with causing loss of nutrients and irrigation water. Over-irrigation leads to water logging and development of soil salinity. It also depletes the groundwater table due to pumping of water. Groundwater is being contaminated with high concentrations of nitrate, fluoride, arsenic and many metal ions. The objective of the paper is to assess the water resources situation in one of the agriculturally developed regions in order to promote integrated planning.Key words Indo-Gangetic ecosystem; sustainable water management; agriculturally developed region; land-use change; snowmelt water


River water sharing: India’s problems

K. S. MURTY101 Sneh Chaya Apts., 28 Hindustan Colony, Amaravati Road, Nagpur 440010, Indiae-mail: [email protected]

Abstract While India came to an agreement with Pakistan, Nepal and Bangladesh to share and utilize the waters of rivers that originate in those countries or pass through them, the sharing of the waters of inter-state rivers has caused severe problems. The Yamuna and the Brahmaputra in the north and the Godavari, the Krishna, and the Kaveri in the south are the main rivers concerned. Under the Indian Constitution, water is a state subject and the Central Government’s role is in the form of overall policy formulation, coordination, guidance and general infrastructural, technical and research support. Sharing of the waters of the Krishna, Godavari and Narmada rivers by the states concerned has been decided by tribunals under the Inter-state Waters Disputes Act, 1956. The Ravi and Beas Water Tribunal decided how to apportion the waters of these rivers in 1987. The states concerned have disagreed in their interpretation and implementation of the decisions made by the tribunals, leading to much acrimony and unpleasantness, which made it necessary to involve the Supreme Court of India itself.Key words river water allocation; Narmada; Krishna; Godavari; Kaveri; Bachawat award; Alamatti dam; India


Water sharing in the Volta basin

MARC ANDREINICenter for Development Research, GLOWA Volta Project, PO Box 645, Tamale, Ghana

PAUL VLEK & NICK VAN DE GIESENCenter for Development Research, Bonn University, Walter-Flex-Strasse 3, D-53113 Bonn, Germanye-mail: [email protected]

Abstract The geography of the Volta basin is briefly described. This is followed by an overview of water use developments in the two main riparian countries, Ghana and Burkina Faso. Ghana’s water use consists mainly of hydropower generation for the urbanized south whereas in upstream Burkina Faso agricultural water use dominates. Analysis of the water balance shows a large sensitivity of surface water resources with respect to changes in precipitation and thereby to global and regional climate change. Finally, the GLOWA Volta project is introduced which addresses the issue of optimal water use under changing water demand and supply.Key words international basins; West Africa; integrated basin management; GLOWA


Vers une approche globale de la gestion de la ressource comme solution aux crises d’eau des dernières décennies au Cameroun

LUC SIGHA-NKAMDJOU, DANIEL SIGHOMNOU & GASTON LIENOUCentre de Recherches Hydrologiques, BP 4110, Yaoundé, Cameroune-mail: [email protected]

Résumé La disponibilité annuelle en eau par habitant est estimée actuellement à 21 000 m3 au Cameroun contre une moyenne mondiale de 7000 m3 hbt-1 an-1, le stress hydrique étant fixé à 1000 m3 hbt-1 an-1 d’après le PNUD. Le Cameroun dispose également d’un potentiel hydro-électrique sauvage estimé à 35 GW. En dépit de cette abondante ressource en eau, la proportion de la population ayant accès à l’eau potable et à l’énergie électrique reste faible (11% pour l’eau potable et 22% pour l’électricité toute source confondue). Cet approvisionnement n’est pas assuré en permanence, de nombreuses coupures d’eau et d’électricité liées à la disponibilité en eau étant fréquemment observées surtout en étiage. Bien que de phénomènes naturels puissent les expliquer, une gestion plus rationnelle des ressources en eau aurait permis d’en limiter les effets. Ce papier suggère une mise en

valeur de la ressource par une approche globale qui prenne en compte les différents secteurs de développement et qui recherche des solutions alternatives ou complémentaires d’approvisionnement au système actuel.Mots clefs ressources en eau; crises d’eau; gestion; bien-être; CamerounKey words water resources; water crises; management; well-being; Cameroon


Déficit, adéquation de l’offre et de la demande en eau et dynamique du bassin de l’Anambé

Adrien ColyTropis–Environnement Sarl, Bureau d’Études et d’Appui au Développement, BP 26405, 56 Rue Raffenel, Dakar, Sénégale-mail: [email protected]

Honoré DacostaDépartement de Géographie, Université Cheikh Anta Diop de Dakar, Sénégal

Pape Ousmane SoumaréLGP CNRS 1, Place Aristide Briand, F-92195 Meudon Cedex, France

Résumé Le déficit pluviométrique observé depuis 1970 a conduit le Sénégal à initier la mise en valeur du bassin de l’Anambé (sud-est du pays). Après deux décennies d’aménagements hydrauliques et hydro-agricoles, les objectifs d’une double culture de riz sur les 16 000 ha assignés à la Société de Développement Agricole et Industriel (SODAGRI) ne sont toujours pas atteints et sont mêmes revus à la baisse. Il apparaît que l’adéquation de l’offre et de la demande désigne la disponibilité de l’eau comme cause principale de cette situation. Le système de l’Anambé fonctionne dans un contexte de déficit hydrique évalué à près de 60% et de nombreuses défaillances sont constatées dans les formes d’usage de l’eau. Les dynamiques observées sont imputables au système utilisateur de la ressource en eau de l’Anambé qui présente toutes les carences liées à l’inexistence d’indicateurs fiables et d’une bonne organisation de l’utilisation des eaux pour une gestion opérationnelle.Mots clefs bassin de l’Anambé; déficit; offre; demande; système d’utilisation; gestionKey words Anambé basin; deficit; supply; user system; water management


Managing the fragile hydrological ecosystem of the northeast hilly region of India for resource conservation and improved productivity

U. C. SHARMANational Agricultural Technology Project, P.I.U., LBS Centre, IARI Campus, New Delhi 110012, Indiae-mail: [email protected]

Abstract The northeastern region of India is endowed with rich natural resources of soils, water and vegetation. Though sparsely populated, the region has a foodgrain shortfall of about 2.1 million tonnes. The annual growth rate of foodgrain production and productivity in the region is 2.19% and 1.48%, whereas the growth in population is 2.43%, indicating that the food shortfall will continue to increase. Practically all very low areas are under cultivation during the winter due to the acute shortage of soil moisture. The average annual runoff of two major rivers in the region is 597 040 Mm3 and the total riverine length is 19 548 km. The region receives about 510 km3 of water annually as rainfall and if properly harnessed, by harvesting this water in suitably located tanks, a greater area could be cultivated during winter. Development of water resources in the region is the key factor for increasing food production.Key words fragile hydrological ecosystem; resource conservation; food security


Sustaining wetland ecosystems in the West and central African Sahel

LEKAN OYEBANDEHydrology Laboratory, Department of Geography, University of Lagos, PO Box 160, Akoka, Lagos 10107, Nigeriae-mail: [email protected]

Abstract The Senegal and the Niger rivers and Lake Chad, the dominant river/lake systems in West Africa had wetlands covering a surface area of about 6.7 106 ha. However, due to the combined effects of climate variability and water projects (dams and dykes), more than 40% of the area had been lost. Yet the Sahel wetlands are the lifelines for the inhabitants of the zone. The wetlands have many uses: for crop and grazing lands, fishing grounds and habitat for wildlife, and these multiple uses yield many products of water, food, fibres and energy. In order to save and sustain the wetland ecosystems certain effective strategic management tools should be employed.Key words wetland ecosystems; multiple products; database; degradation; sustainable management; Sahel


Modelling of regional changes of riverine nitrogen flow in the Svartå River, Sweden

LOTTA ANDERSSONDepartment of Water and Environmental Studies, Linköping University, S-58183 Linköping, Swedene-mail: [email protected]

Berit ArheimerSwedish Meteorological and Hydrological Institute, S-60176 Norrköping, Sweden

Abstract The HBV-N model was used to evaluate effects from changes (1885–1994) of land use, agricultural practices, N-deposition, food consumption, introduction of water closets, lowering of lakes, building of dams, and of climatic variability on N-transport from a river basin (1400 km2) in south central Sweden. Drainage of agricultural land had an overriding impact on N-load, compared to the effect of lowering of lakes and building of dams. This was because previously poorly drained areas had a geographical extension that was approximately 200 times larger than areas affected by alterations of open-water surfaces. Compared to human-induced alteration of N-retention, the selection of a 10-year period of climatological data had an overriding effect on the calculated average annual nitrogen transport. The overall change over time of riverine N-transport mainly reflected changes of the contribution from agricultural land, although also household emissions increased drastically over the period studied.Key words nitrogen load; retention; climatic variability; historical changes; modelling; riverine; river basin; Sweden


Caractéristiques hydrologiques et géochimiques d’un bassin élémentaire en zone tropicale humide d’Afrique: le bassin versant expérimental de Nsimi–Zoétélé (sud-Cameroun)

JULES REMY NDAM NGOUPAYOUDST, Faculté des Sciences, Université de Yaoundé I, BP 812 Yaoundé, Cameroune-mail: [email protected]

JEAN-JACQUES BRAUNLMTG UMR 5563, 38 Rue des 36 Ponts, F-31400 Toulouse, France

JEAN-LOUP BOEGLINInstitut de Recherche pour le Développement (IRD), BP 1857, Yaoundé, Cameroun

MICHEL MEYBECKSisyphe, UPMC Paris VI, case 123, T26-5étage, 4 Place Jussieu, F-75252, Paris Cedex 05, France

LUC SIGHA NKAMDJOU, DANIEL SIGHOMNOU & JEAN-PIERRE BEDIMOCentre de Recherches Hydrologiques, IRGM, BP 4110, Yaoundé, Cameroun

Résumé Une étude pluridisciplinaire (hydrologie, géochimie, cristallographie, géophysique, microbiologie et pédologie) est menée depuis 1993 sur le bassin versant expérimental de Nsimi. Cette note présente les principaux résultats acquis aux niveaux hydrologique et géochimique sur ce petit bassin élémentaire considéré comme observatoire naturel de l’écosystème tropical humide du sud-Cameroun. La pluie moyenne interannuelle (1700 ± 145 mm) est répartie chaque année sur quatre saisons d’inégales importances; le débit spécifique (11.4 l s-1 km-2) est identique à celui des affluents du réseau fluvial du Nyong. Les hydrogrammes de crue montrent généralement une réponse quasi instantanée quelle que soit la période de l’année. Un fort contraste géochimique est observé au niveau des différents compartiments fonctionnels de ce bassin (pluies et pluviolessivats, nappes de versants et de la zone marécageuse, ruisseau Mengong). La zone marécageuse (20% du bassin versant expérimental) régule l’écoulement du ruisseau grâce à sa saturation permanente et joue un rôle très actif dans la mobilisation des éléments dissous et particulaires du fait de la présence de la matière organique.Mots clefs hydrologie; chimie des eaux; carbone organique dissous; zone marécageuse; érosion et altération; écosystème tropical humide; CamerounKey words hydrology; hydrochemistry; dissolved organic carbon; swampy zone; erosion and weathering; humid tropical ecosystem; Cameroon


Extreme stages of the basin wetness conditions. Variability of the soil moisture in a lowland basin

URSZULA SOMOROWSKAFaculty of Geography and Regional Studies, Warsaw University, Krakowskie Przedmiescie 30, 00-927 Warsaw, Polande-mail: [email protected]

Abstract The extreme stages of the wetness conditions in a basin derived from direct soil moisture measurements are investigated. Current variability of soil moisture and soil water storage is estimated in the Lasica basin, situated in central Poland on the Mazovian Lowland, within the boundaries of the Kampinos National Park. Temporal decrease of soil water storage is presented as a function of groundwater level change and storage coefficient. The range of the water storage variability is presented in a spatially distributed way. Results can be used as a basis for restoration of wetness conditions facilitating the re-development of natural vegetation.Key words soil moisture; time domain reflectometry (TDR); water storage decrease function; Kampinos National Park; central Poland; spatial variability


A compensatory forestry approach to clearing alien invasive vegetation from riparian zones in a South African basin

G. P. W. JEWITT, M. C. HORANSchool of Bioresources Engineering and Environmental Hydrology, University of Natal, Private Bag X01, Scottsville 3209, KwaZulu-Natal, South Africae-mail: [email protected]

K. B. MEIERLand Resources International, PO Box 252, Pinetown 3610, KwaZulu-Natal, South Africa

Abstract In South Africa, it is accepted that widespread invasive alien vegetation is impacting negatively on biodiversity and water resources. Water resource management now includes consideration of invasive alien plant management. It has been suggested that in some areas of the country, the clearing of alien vegetation in riparian zones may be compensated for by the establishment of commercial plantations elsewhere in a basin, and still result in an improvement of the water supply and an economic benefit to the grower. A case study in KwaZulu-Natal province in which hydrological impacts of possible land-use changes associated with this so-called “compensatory forestry” are simulated with the use of the ACRU agrohydrological model, and the results then linked to an economic analysis is presented. Results indicate that clearing of alien invasive vegetation in the riparian zones and the establishment of commercial timber plantations in optimal areas of the basins will have both hydrological and economic benefits.

Key words compensatory forestry; alien invasive vegetation; riparian zone; ACRU; South Africa; working for water


Sustaining water-related ecosystems—the role of in-stream bedform design in river channel rehabilitation

NICHOLAS J. CLIFFORD, PHILIP J. SOARSchool of Geography, University of Nottingham, Nottingham NG7 2RD, UKe-mail: [email protected]

JOANNE C. EMERY, ANGELA M. GURNELL & GEOFFREY E. PETTSSchool of Geography and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK

Abstract This paper explores the role of riffle-pool bedforms in functional eco-hydraulic river rehabilitation designs and addresses the need for quantitative means of generalizing flow behaviour. Riffle hydraulic performance is modelled using a cross-sectionally disaggregated form of broad crested weir equation. For a given channel reach, geostatistical analysis of mapped flow velocity at contrasting flow stages is then used to identify coherent flow behaviour which might be related to channel bedform morphology and hydraulic function. Finally, observed and inferred flow characteristics are reviewed against the data requirements of habitat simulation models and with respect to the application flow simulation modelling. By coupling morphology, flow characterization and habitat modelling, the aim is to provide a simple, but scientifically sound approach for assessing the eco-hydraulic performance of channel bedforms to improve both project design and post-project audit of rehabilitation schemes.Key words eco-hydraulics; flow modelling; geostatistics; physical habitat simulation; riffle-pool bedforms; river rehabilitation


Himalayan glaciers meltdown: impact on south Asian rivers

SYED IQBAL HASNAINSchool of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110067, Indiae-mail: [email protected]

Abstract The Himalaya mountains contain the largest volume of ice outside the polar regions. About 17% of the Himalaya and 37% of Karakoram mountains are covered by glacier ice. The meltwaters from its glaciers form the headwaters of major rivers as the Indus, the Ganges and the Brahmaputra. The discharge of headwater rivers comprises about 70–80% of snow and ice melt. In recent years the summers have been particularly warm as average air temperatures have risen rapidly by more than 1.5°C, increasing the year to year variability of river flow. The majority of Himalayan glaciers are nourished by the precipitation during the summer-monsoon and therefore they are very sensitive to summer air temperature fluctuations. This paper will examine how climate change influences glacier behaviour and the quantity of discharge in rivers draining from glaciated Himalayan basins. A case study of the Dokriani Glacier (Ganga headwaters, India) is presented.Key words glacier meltwater; global climate; south Asian rivers; summer-accumulation glaciers; Dokriani Glacier; Ganga; India


Flow regime characteristics of Himalayan river basins in Nepal

SUNIL R. KANSAKAR, DAVID M. HANNAH, JOHN GERRARDSchool of Geography and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UKe-mail: [email protected]

GWYN REESCentre for Ecology and Hydrology, Wallingford, Oxfordshire OX10 8BB, UK

Abstract A large-scale perspective on the nature and geography of Himalayan river flow regimes across Nepal is provided using mean monthly flow data for 36 river basins. A classification approach is used to group annual regimes according to their “shape” and “magnitude”. The results suggest that the timing and length of the monsoon control “shape” regime and precipitation amount determines the “magnitude” regime. For regime “shape”, July–September peaks are typical of central basins at lower altitudes; July–August peaks are characteristic of central basins at moderate to high altitudes and eastern higher mountains; and August peaks are confined to western basins and higher mountains. Low, intermediate and high “magnitude” regime classes correspond with basin rainfall totals; and their distribution is explained by decreasing rainfall gradients from east to west and from south to north. Localized pockets of classes exist possibly due to the affect of topography on rainfall and basin characteristics in the controlling regime.Key words river flow; regimes; regionalization; classification; Himalayas; Nepal


Application of the regional flow estimation method in the Himalayan region

GWYN REES, KAREN CROKER, MAXINE ZAIDMAN, GWYNETH COLECentre for Ecology and Hydrology Wallingford, Oxfordshire OX10 8BB, UKe-mail: [email protected]

SUNIL KANSAKARDepartment for Hydrology and Meteorology, Babar Mahal, PO Box 406, Kathmandu, Nepal

SURESH CHALISEMountain Natural Resources Division, International Centre for Integrated Mountain Development (ICIMOD), PO Box 3226, Kathmandu, Nepal

ARUN KUMAR, ARUN SARAF & MUKESH SINGHALAlternate Hydro Energy Centre, University of Roorkee, Roorkee 247667, India

Abstract The regional flow estimation method (RFEM) has been used in the UK and Europe for many water resources planning applications. The method, which is based on the fact that the temporal variability of flows at any point in a river is controlled by the physical characteristics of the upstream basin, provides an estimate of the flow–duration curve at ungauged sites. This paper describes the adaptation of the method in Nepal and the Indian state Himachal Pradesh; a region typified by high mountains and a monsoon-dominated climate and having relatively sparse hydrometric and meteorological observations. By relating the observed river flow data to pertinent basin characteristics, regional statistical models, capable of describing the flow regime at any location in the study area, were derived. Though the data available to the project was limited, the results were generally satisfactory, comparing favourably with those from similar studies in Europe.Key words regional models; multivariate regression; flow–duration curves; ungauged basins; Himalayan region; Nepal; Himachal Pradesh


Change of hydrological regimes over the central part of European Russia resulting from climate variations

S. A. ZHURAVINState Hydrological Institute, 23 Second line, 199053 St Petersburg, Russiae-mail: [email protected] or [email protected]

Abstract Change of continental and regional hydrological regimes resulting from long-term climate variations is one of the most urgent problems in the world. This problem is extremely relevant for the central part of European Russia, the most populated and developed part of the country. A visible trend in climate data is observed that indicates climate change. In the region the annual air temperature and precipitation, in particular, show a stable, increasing trend over the last 90–110 years. The analysis illustrates both favourable and

unfavourable consequences of these changes for the hydrological regimes. An increase of low flows of the large and mid-size rivers and water storage in aquifers are positive, whereas drying up of small rivers and water courses, and more severe soil droughts are negative. The reasons and consequences of these events are considered in this study using available standard and experimental hydrological data.Key words climate change; hydrological regimes; regional long-term variations; water balance components


Evidence d’une modification du régime hydrologique du fleuve Niger à Niamey

ABOU AMANI & MADJYARA NGUETORACentre Régional AGRHYMET, Programmes Majeurs Formation et Information, BP 11011, Niamey, Nigere-mail: [email protected]

Résumé L’analyse de la série des débits journaliers du fleuve Niger à Niamey de 1928 à 2000, montre une modification manifeste du régime hydrologique à cette station. Les débits à Niamey découlent de la superposition des écoulements en provenance du bassin supérieur et ceux des affluents de la rive droite (Sirba, Gorouol, Dargol). Les modifications observées des hydrogrammes du Niger à Niamey sont liées principalement à la baisse des écoulements au niveau du haut bassin et à la dégradation du couvert végétal et du sol au sein des bassins des affluents de la rive droite favorisant dans une certaine mesure l’augmentation du coefficient de ruissellement au sein de ces bassins. L’hydrogramme de crue à la Sirba est analysé conjointement avec l’hydrogramme de crue à Niamey afin d’expliquer les modifications de régimes observées à Niamey. Cette modification explique le fait que des crues importantes voire exceptionnelles sont observées ces dernières années en période hivernale à Niamey.Mots clefs régime hydrologique; fleuve Niger à Niamey; modification; SirbaKey words hydrological regime; Niger River at Niamey; regime modification; Sirba


Spatial and temporal variability of UK river flow regimes

DONNA BOWER & DAVID M. HANNAHSchool of Geography and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UKe-mail: [email protected]; [email protected]

Abstract This paper investigates the spatial distribution and temporal stability of annual flow regimes within the UK, using 25-year records for 35 gauging stations. A multivariate, statistical classification of regime “shape” and “magnitude” is used: (a) to regionalize long-term average regimes and (b) to establish inter-annual variability (stability) in regimes at stations and within “regions”. Regionalization yields four “shape” classes with different timing of major flow peaks and three “magnitude” classes. Stability analysis identifies six “shape” and four “magnitude” classes. These results suggest regime “shape” is controlled by the seasonal distribution and nature of hydroclimatic inputs. Although regime “magnitude” decreases along a west–east precipitation gradient at the UK scale, inter-annual variations in “magnitude” at a station may be linked to large-scale atmospheric circulation patterns, particularly during the autumn recharge season. Both regime “shape” and “magnitude” are influenced by geology; basins associated with major aquifers exhibit greater stability in regime “shape”. However, strong synoptic climatological forcing may cause a single regime type to dominate across the UK.Key words river flow; regimes; hydroclimatology; regionalization; classification; UK


Régionalisation de la pluviométrie sur l’espace riverain de l’océan Indien et prévision statistique à moyen terme

BERTRAND DUCHIRONLODYC (UMR 7617), Université Pierre et Marie Curie, cc100, 4 Place Jussieu, F-75252 Paris Cedex 05, France

e-mail: [email protected]

GÉRARD BELTRANDOUMR PRODIG, Université Denis Diderot, Centre de Géographie Physique, 2 Place Jussieu, F-75251 Paris Cedex 05, France

Résumé À partir de la base de données climatologiques du Global Historical Climatic Network, un réseau de 130 stations météorologiques réparties autour de l’océan Indien est utilisé pour définir 21 régions considérées comme pluviométriquement homogènes, sur la période 1946–1975. Les données du fichier COADS en point de grille, sont utilisées pour définir 10 zones sur l’océan Indien et deux sur l’océan Pacifique ouest afin de quantifier la circulation océano-atmosphérique de surface. Des modèles LOGIT sont utilisés pour estimer le sens positif ou négatif de l’écart à la moyenne mensuelle sur 30 ans (1946–1975) avec un décalage temporel de 1, 2 et 3 mois. Les résultats sont montrés pour deux régions à pluviométrie contrastée (Kenya et Java) où les modèles donnent de bons résultats. Avec 1, 2 et 3 mois de décalage, une prévision du sens positif ou négatif de la tendance pluviométrique mensuelle par rapport à la moyenne est fiable à plus de 70% au cœur des saisons pluvieuses pour ces deux régions.Mots clefs modèles probabilistes (LOGIT); océan Indien; spatialisation pluviométrique; prévision pluviométrique à moyen termeKey words probabilistic models (LOGIT model), Indian Ocean; rainfall spatial distribution; medium-term rainfall forecast


The hydrological effects of two extreme rainfall events over East Africa: 1961 and 1997

DECLAN CONWAYSchool of Development Studies, University of East Anglia, Norwich NR4 7TJ, UKe-mail: [email protected]

Abstract An assessment of the hydrological effects of the two most extreme October–November rainfall events in East Africa during the twentieth century is provided. Flow records for major rivers draining large parts of East (White Nile and Tana), central (Congo and Oubangui), the Horn (Blue Nile and Atbara) and southern Africa (Zambezi) are used for the analysis. During and after the 1961 event flooding was widespread throughout the region. Between 1961 and 1964 the cumulative excess volume of flow above the 1961–1990 mean of all the rivers analysed was 357 km3 year-1. The availability of hydrological data for 1997 is restricted to the Blue Nile (unexceptional flows), Congo (very high flows) and Lake Victoria (significant rise in lake level). The historical records are surveyed for possible precedents to these events and the year most similar is 1878, which is generally noted as an extremely wet year across the region.Key words rainfall; extremes; flooding; East Africa; Nile


Space–time rainfall variability in West Africa derived from observations and GCMs

HUBERT ONIBON, THIERRY LEBELLTHE/IRD, 1025 BP 53 Domaine Universitaire, F-38041 Grenoble Cedex 9, Francee-mail: [email protected]

ABEL AFOUDAUniversité Nationale du Bénin, BP 526, Cotonou, Benin

Abstract The CATCH project quantifies the impact of climate variability on water resources in West Africa by using observed and simulated rainfall scenarios as input for hydrological models. The reliability of the rainfall of a global circulation model (GCM) (LMD-6) was investigated over the CATH region (0° to 5°E and 6° to 15°N). Observed daily rainfall data between 1960 and 1990, spatially averaged over the five selected GCM cells, were compared with the GCM rainfall to identify which variability is reproduced. This includes the seasonal cycle, the inter-annual variability and daily rainfall characteristics. Substantial discrepancies between the observed and simulated rainfall regime of West Africa were found.

Key words global circulation model (GCM); rainfall; simulation; observation; variability; season; climate; West Africa


Evidence of scaling properties in West African rainfall

ABEL AFOUDAUniversité Nationale du Bénin, BP 526, Cotonou, Benine-mail: [email protected]

THIERRY LEBEL, HUBERT ONIBON, WILLIAM SACHER, LUC LE BARBE, CHRISTIAN DEPRAETERELTHE/IRD, 1025 BP 53 Domaine Universitaire, F-38041 Grenoble Cedex 9, France

GREGOIRE ALEDirection de l’Hydraulique, BP 385, Cotonou, Benin

Abstract Many studies have been carried out to analyse rainfall variability in tropical West Africa. Most generally these studies focused on the permanent imbalance between precipitation and potential evapotranspiration and tried to explain rainfall variability statistically in terms of dry and wet periods. In recent years, the use of general circulation models (GCMs) has prompted many researchers to consider the gaps between meteorological and hydrological scales. Driven by the observation of scale invariance in rainfall fields, a new class of self-similar models is being developed. In tropical West Africa where rainfall is highly variable in space and time due to its convective origins and where ground-based rain measurements are scarce due to low-density networks, understanding and quantifying the space–time dependencies of rainfall over a range of scales is not an easy task. In this paper we report our efforts to understand the space–time organization of event rain-fields over a range of scales: from 5 minutes to several hours for raw event rain depths and from one day to 31 years for maximum event rain depths.Key words West Africa; convective system; variability; scaling; turbulent process; power law; Markov property


La variabilité spatio-temporelle des précipitations au Sénégal depuis un siècle

HONORÉ DACOSTA, KONATE YAYE KANDIADépartement de Géographie, Faculté des Lettres et Sciences Humaines, Université Cheikh Anta Diop de Dakar, BP 5005 Dakar-Fann, Sénégale-mail: [email protected]

RAYMOND MALOUDépartement de Géologie, Faculté des Sciences et Techniques, Université Cheikh Anta Diop de Dakar, BP 5005 Dakar-Fann, Sénégal

Résumé Les premières mesures pluviométriques, au Sénégal, remontent à 1854 à Saint-Louis. Après plus d’un siècle d’observations, l’analyse des séries chronologiques de pluies annuelles montre, au plan temporel, des fluctuations constantes avec une rupture à la fin des années 1960. Cette dernière divise les chroniques de pluies annuelles en deux sous-ensembles aux caractéristiques statistiques distinctes. Cette date de rupture varie de la côte vers l’intérieur du continent et du sud au nord. Au plan spatial, on note une migration des isohyètes vers le sud avec une nette différence entre zone côtière et domaine continental. Une analyse de la composante méridienne à travers trois transects (17° correspondant à la côte; 15° et 12°) indique une zonation de la distribution des précipitations et une différenciation entre zones climatiques.Mots clefs Sénégal; précipitations annuelles; variation; spatiale; temporelle; isohyètes; séries chronologiquesKey words Senegal, annual rainfall; spatio-temporal variability; isohyets; time series


Stabilité interannuelle des précipitations en Côte d’Ivoire de 1950 à 1996

S. BigotLaboratoire de Géographie des Milieux Anthropisés (CNRS-FRE2170), Université des Sciences et Technologies de Lille, Avenue Paul Langevin, F-59655 Villeneuve d’Ascq, Francee-mail: [email protected]

T. Brou YaoInstitut de Géographie Tropicale, Université de Cocody, 22 BP 744, Abidjan 22, Côte d’Ivoire

V. BONNARDOTARC-ISCW, Nietvoorbij Institute, Private Bag X5026, Stellenbosch 7599, Afrique du Sud

E. SERVATInstitut de Recherche pour le Développement, BP 5045, F-34032 Montpellier Cedex 1, France

Résumé A partir de l’analyse multivariée menée conjointement, grâce à une singular value decomposition, sur 42 séries pluviométriques de la Côte d’Ivoire et sur les champs thermiques de surface de l’océan Atlantique pour la période 1950–1996, trois modes couplés sont discriminés. A travers ces modes statistiques, analysés dans leurs modulations d’amplitude interannuelles, il est possible de mettre en évidence certaines téléconnexions océano-atmosphériques, impliquant à la fois la circulation méridienne atlantique mais aussi la circulation zonale forcée par le Pacifique, qui influencent les variations pluviométriques régionales de la Côte d’Ivoire.Mots clefs précipitations; Côte d’Ivoire; températures de surface océanique; océan Atlantique; singular value decomposition; variabilité spatio-temporelleKey words rainfall; Ivory Coast; sea surface temperature; Atlantic Ocean; singular value decomposition; spatio-temporal variability

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