Analysis of the water temperature regime of the Danube and its tributaries in Croatia

HYDROLOGICAL PROCESSESHydrol. Process. 22, 1014–1021 (2008)Published online 31 January 2008 in Wiley InterScience(www.interscience.wiley.com) DOI: 10.1002/hyp.6975

Analysis of the water temperature regime of the Danubeand its tributaries in Croatia

Ognjen Bonacci,1* Dusan Trninic2 and Tanja Roje-Bonacci3

1 Faculty of Civil Engineering and Architecture, University of Split, Matice hrvatske 15, 21000 Split, Croatia2 Meteorological and Hydrological Service, Gric 3, 10000 Zagreb, Croatia

3 Faculty of Civil Engineering and Architecture, University of Split, Matice hrvatske 15, 21000 Split, Croatia

Abstract:

Changes in water temperature along stretches of the Kupa, Sava, Drava and Danube Rivers measured in Croatia during thelast 20–60 years were investigated. Characteristic (minimum, mean and maximum) annual water temperatures measured at15 discharge and water temperature stations are analysed. Massive construction on the Danube River basin and on the riversthemselves during the last centuries, as well as recent climate change and/or variability has caused many different and possiblydangerous changes to its water temperature regime. Water temperature, as one of the most important physical characteristicsof river water, strongly affects all other physical, chemical and biological processes in the river system. The investigationfocuses on changes that have occurred during the last 20-odd years, probably caused by climate change and/or variability.Methods of rescaled adjusted partial sums (RAPS) as well as regression and correlation analyses are used in order to explainchanges in water temperature regimes. The water-air temperature relationship is also discussed in the article. In all analysedcases, water temperature is strongly and directly affected by air temperature. There is evidence in the time series of rises inthe minimum and mean annual water temperatures of the River Danube and its main tributaries in Croatia (the Kupa, Savaand Drava Rivers). The rising of mean annual air as well as water temperatures is shown to have started in 1988. Copyright 2008 John Wiley & Sons, Ltd.

KEY WORDS water temperature; air temperature; Kupa; Sava; Drava; Danube Rivers (Croatia)

Received 5 August 2007; Accepted 26 November 2007

INTRODUCTION

Temperature represents one of the most important phys-ical characteristics of river water, which affects its otherphysical properties and influences the chemical and bio-chemical reactions in its lotic system (Walling and Webb,1992). Water temperature integrates landscape influencesand can be a useful parameter for the examination ofsources, residence times and interchanges of stream waterwithin landscapes. The evolution, distribution and ecol-ogy of aquatic organisms are fundamentally affected byriver temperature (Rose, 1967). Gore (1992) stresses thatthe life cycle of lotic biota is regulated by the river’stemperature, and its hydrologic and hydraulic conditions.In addition, the temperature and length of day are regu-lating features that synchronize hatching, maturation oflarvae, emergence and mating of adults and egg-layingbehaviour (Gore, 1992).

Without detailed investigations of the water tempera-ture regime, it is not possible to understand and explainthe complex ecological processes of the river system.This is especially important in recent times, when a trendto the rising of air, as well as river temperatures arenoted in many world regions (Webb and Nobilis, 2007;Zweimuller, 2007). Explaining the relationship between

* Correspondence to: Ognjen Bonacci, Faculty of Civil Engineering andArchitecture, University of Split, Matice hrvatske 15, 21000 Split,Croatia. E-mail: [email protected]

air and water temperatures is extremely important. Thiswork is needed as a response to projections of a futureincrease in air temperature.

The river temperature is at the same time a physical(hydrological) and water quality (ecological and chem-ical) parameter. Investigation of the water temperatureregime can be understood as a part of an interdisciplinaryapproach to river system analysis, and as an inevitableelement of a new emerging scientific concept called eco-hydrology (Zalewski, 2002), which tries to understand,explain and use links between hydrology and ecology.Water temperature is a crucial parameter for both thesefields, and it is a critical factor in the stream ecosystem.

Webb and Nobilis (2007) consider the fact that lessattention has been focused on past trends in river temper-ature partly reflects a general dearth of long, reliable andunbroken records. This article is based on water temper-ature records of differing length from the Danube Riverand three larger Croatian watercourses (the Kupa, Savaand Drava), which belong to the Danube River catch-ment. Data are based on daily observations with a liquidthermometer.

The purpose of this article is to analyse records ofwater and air temperature, and to explain recent changesin water temperature records in some larger Croatianrivers that belong to the Danube River catchment. Inthe rivers Kupa and Drava there are eight and fourwater temperature gauging stations, respectively. This

Copyright 2008 John Wiley & Sons, Ltd.

WATER TEMPERATURE (CROATIA) 1015

fact enables analyses of water temperature behaviour tobe taken along their watercourses.

There are many and various interrelations, on spaceand time scales, between water and air temperatures. Inone paper, it is not possible to consider all of them. Owingto this reason, the main objective of this article is ananalysis of long-term trends in air and river temperatureson the Danube River and some of its larger tributaries inCroatia. The annual minimum, maximum and average airand water temperatures in the study area will be discussedhere.

STUDY AREA

The study area is located in the northern continental partof Croatia (Figure 1(a)) between 44°520 and 46°330N,and 14°260 and 18°500E. Figure 1(b) is a schematicpresentation of the four analysed rivers (Kupa, Sava,Drava and Danube) with the designated positions of the15 water temperature gauging stations (four on the RiverDrava, two on the River Sava, eight on the River Kupaand one on the River Danube) and two meteorologicalstations (Zagreb and Osijek). Table I presents the maincharacteristics of all 15 analysed water temperaturegauging stations (river, station name, datum plane H,basin area A, distance from mouth L, period of availabledata and mean annual discharge in available period Q).

It should be stressed that all the analysed rivers partlyor mostly represent boundaries between Croatia and itsneighbouring states: Slovenia (Kupa), Hungary (Drava),Bosnia and Herzegovina (Sava) and Serbia (Danube).This fact emphasizes the importance of water temperature

analyses. Except the upper part of the River Kupa (abovethe Kamanje gauging station), the whole study area is partof the Pannonia Valley, whose climate is continental.

Practically the whole flow of the River Kupa, from itsabundant karst spring to the mouth in the River Sava,is covered by eight water temperature gauging stations.The lower part of the River Drava, above the confluencewith the River Danube, is included in this article. Alongthis river sector there are four water temperature gaugingstations, but no significant tributaries, so that mean annualdischarge only changes from 502 m3/s at Botovo to550 m3/s at Osijek (Table I), over a distance of morethan 200 km. The central part of the River Sava, fromthe Slovenian-Croatian to the Croatian-Serbian boundary,is analysed here. Only two water temperature gaugingstations exist on this long reach where many tributaries,coming from Bosnia and Herzegovina, enter the RiverSava.

Large engineering works in the whole Danube basinand on the rivers themselves, constructed during pastcenturies, have caused many different changes to thehydrological, morphological as well as air and watertemperature regimes along the River Danube, and itstributaries in Croatia (Bonacci and Trninic, 1991; Bonacciet al., 1992; Bonacci and Ljubenkov, 2007).

AIR TEMPERATURE

Air temperature is the main factor affecting water temper-ature (Webb and Nobilis, 1997; Ahmadi-Nedushan et al.,2007). In this article data from meteorological stationsin Zagreb and Osijek for the period 1900–2005 are used

Figure 1. Location maps indicating (a) the study area and (b) schematic presentation of the four study rivers with the sites of fifteen water temperaturegauging stations and two meteorological stations

Copyright 2008 John Wiley & Sons, Ltd. Hydrol. Process. 22, 1014–1021 (2008)DOI: 10.1002/hyp

1016 O. BONACCI, D. TRNINIC AND T. ROJE-BONACCI

Table I. Main characteristics of 15 analysed water temperature gauging stations

River Stationname

ElevationH (m a.s.l.)

Basinarea A(km2)

Distancefrom mouth

L(km)

Periodof available

data

Meanannual

discharge Q(m3/s)

Danube Vukovara 76Ð19 250 000 1337 1948–2005 2820Sava Zagrebb 112Ð26 12 450 664 1948–1998 311

Slavonski Brodc 81Ð80 50 828 364 1956–1998 1016Drava Botovo 121Ð55 31 038 227 1969–2005 502

Terezino Polje 100Ð67 33 916 152 1969–2005 517Donji Miholjac 88Ð39 37 142 75 1948–2005 530

Osijek 81Ð48 39 982 19 1948–1991 550Kupa Kupari 304Ð43 208 290 1956–1991 13Ð5

Hrvatsko 285Ð28 355 286 1965–2003 20Ð2Ladesic Draga 147Ð76 1445 205 1964–1990 59Ð1

Kamanje 123Ð83 2047 171 1968–1986 73Ð2Karlovac 103Ð17 3461 133 1968–1989 165Sisinec 94Ð81 7364 65 1968–1986 183Farkasic 93Ð85 8992 47 1968–1986 195

Sisak 90Ð59 11 449 3Ð5 1951–1986 230

Data missing for: Vukovar a 1952, 1991–2001; Zagreb b 1949–1952, 1954, 1991–1992 and 1996–1997; Slavonski Brod c 1991–1992 and 1996–1997.

to analyse regional air temperature characteristics. TheZagreb meteorological station is located at the westernedge of the study area, while the Osijek meteorologi-cal station is located at the eastern edge (Figure 1). Thedistance between them is about 220 km.

Table II gives characteristic (minimum, average andmaximum) annual, monthly and instantaneous air temper-ature measured at the Zagreb and Osijek meteorologicalstations for the period 1900–2005. Figure 2 presents anannual time series of monthly minimum, average andmaximum air temperature for Zagreb and Osijek. Datagiven in Table II and Figure 2 present clear evidencethat regional air temperature in the study area is gen-erally homogenous. This conclusion can be confirmed bythe fact that the linear regression equation between meanmonthly air temperature values for Zagreb TZ and OsijekTO during the analysed period (1900–2005) is as follows:

TZ D 0Ð936 ð TO C 1Ð39 �1�

with a very high linear correlation coefficient, R D 0Ð996.

Table II. Characteristic (minimum, average and maximum)annual, monthly and instantaneous air temperature measuredat Zagreb and Osijek meteorological stations for the period

1900–2005 given in °C

Air temperaturecharacteristic

Zagreb Osijek

Elevation (m a.s.l.) 157 88Minimum annual 9Ð70 8Ð80Average annual 11Ð62 10Ð94Maximum annual 13Ð80 12Ð90Minimum monthly �7Ð2 �9Ð3Maximum monthly 25Ð8 25Ð2Minimum instantaneous �22Ð2 �26Ð4Maximum instantaneous 40Ð3 39Ð6

Figure 2. Annual time series of monthly minimum, average and max-imum air temperatures for Zagreb and Osijek meteorological stations

during the period 1900–2005

The annual air temperature time series measured from1900 to 2005 for the Zagreb meteorological stationis presented in Figure 3, and evidences a trend ofincreasing mean annual, as well as minimum annual airtemperatures. Practically the same trends of temperatureincrease are observed for the Osijek meteorologicalstation. It should be stressed that no equivalent trendexists for the maximum annual air temperatures.

A time series analysis can detect and quantify trendsand fluctuations in records. In this article, the rescaledadjusted partial sums (RAPS) method (Garbrecht and Fer-nandez, 1994) was used for this purpose. A visualizationapproach based on RAPS overcomes small systematicchanges in records and the variability of data values. TheRAPS visualization highlights trends, shifts, data cluster-ing, irregular fluctuations, and periodicities in the record(Garbrecht and Fernandez, 1994). It should be objective,but the RAPS method is not without shortcomings. Thevalues of RAPS are defined by:

RAPSk Dk∑

tD1

Yt � Y

SY�2�



Figure 3. Time series of mean annual air temperatures at Zagreb with alinear trend line for the period 1900–2005

where Y is the sample mean; SY is the standard deviation;n is the number of values in the time series; and (k D 1,2. . ., n) is the limit of the summation. The plot of theRAPS in time is the visualization of the trends andfluctuations of Yt.

The time series of RAPS for the mean annual airtemperature at the Zagreb meteorological station for theperiod 1900–2005 is presented in Figure 4. On the basisof this analysis, the data series was divided into twosubsets: (1) 1900–1987; (2) 1988–2005 (Figure 5). TheRAPS method shows that a linear increase in Zagreb andOsijek air temperatures does not exist over the studyperiod, 1900–2005. It indicates that increases of airtemperature at the study meteorological stations startedin 1988 and lasted until 2005. During the first sub-period,temperatures did not increase. In order to investigate thesignificance of the difference between the averages oftwo time sub-series for air temperatures, the t-test wasused. The averages 11Ð47 °C for the 1900–1987 sub-period, and 12Ð36 °C for the 1988–2005 sub-period arestatistically significant (p < 0Ð01). The behaviour of airtemperature (average annual, as well as minimum annual)is identical at the Osijek meteorological station, as wellas some other stations in the region.

WATER TEMPERATURE

Webb and Nobilis (2007) stress that in the time series ofAustrian rivers there is evidence of more rapid rises in

Figure 4. Time data series of the rescaled adjusted partial sums (RAPS)for the mean annual air temperature at Zagreb for the period 1900–2005

Figure 5. Trends in mean annual air temperature of Zagreb in the twosub-periods are defined in Figure 4

water temperature after 1970, and that the last 10 yearsof the 20th century have not seen any diminishing in thetrend of rising temperature. Zweimuller (2007) reportsthat the mean water temperature of the Austrian Danubehas increased by approximately 1 °C per decade overthe last few decades. Significant increases were found inthe winter and the summer, whereas autumn and springtemperatures remained fairly constant.

River water temperature is a relatively simple and inex-pensive variable to monitor. Monitoring of water temper-ature in Croatia is based on a once-daily measurement at7Ð30 am. From Table I, which gives the main charac-teristics of the 15 water temperature monitoring sites, itcan be seen that the duration of water temperature timeseries are different between sites and that there are somemissing data. For the three gauging stations, there areseveral years with incomplete measurements, and data foronly the hot or cold part of year (Zagreb and SlavonskiBrod, 1954 and 1991–1992; Vukovar 1991) were avail-able and could provide information for only the minimumand maximum annual water temperatures for these years.

Mean annual water temperature

Figure 6 presents a time series of mean annualwater temperatures for the River Danube at Vukovar(1948–2005, with some data missing for 1952 and1991–2001), and includes a linear trend line for the studyperiod, which evidences an increase of about 0Ð025 °C peryear. From the beginning of measurements to 2005, themean annual water temperatures rose to about 1Ð5 °C.

Figure 7 presents a time series of mean annual watertemperatures for the River Sava at Zagreb (1948–1998,with some data missing 1949–1952, 1954, 1991–1992and 1996–1997) and at Slavonski Brod (1956–1998,with some data missing for 1991–1992 and 1996–1997),and includes linear trend lines for these periods. Anincrease of about 0Ð012 °C per year is evident, and fromthe beginning of measurements to 2005, the mean annualwater temperature rose by about 0Ð75 °C, which is halfthe increase observed for the River Danube at Vukovar.The mean annual water temperature at Slavonski Brod,300 km downstream, was about 1 °C higher than atZagreb.



Figure 6. Time series of mean annual water temperatures in the RiverDanube at Vukovar

Figure 7. Time series of mean annual water temperature in the River Savaat Zagreb

Figure 8 depicts a time data of mean annual watertemperature for the River Drava at Donji Miholjac forthe 1948–2005 period, and includes linear and poly-nomial trend lines. A trend of temperature increase, ofabout 0Ð016 °C per year, is evident, but a polynomialtrend is more appropriate then a linear one. The timeseries of RAPS for the mean annual water temperatureat Donji Miholjac (Figure 9) suggests division of thedata into two subsets: (1) 1948–1987; (2) 1988–2005(Figure 10). The RAPS analysis indicates that an increas-ing linear trend of water temperature did not occur inthe period, 1948–2005. However, the analysis indicatesthat increases of water temperature started in 1988 andcontinued until 2005. In fact, during the first sub-period(1948–1987) a trend of decreasing temperature is indi-cated. In order to investigate the significance of thedifference between the averages of the two temperaturesub-series, the t-test was used. This suggests the averages,11Ð01 °C for 1948–1987 and 11Ð87 °C for 1988–2005, aredifferent at the p < 0Ð01 level of significance.

Maximum annual water temperature

Figure 11 presents the time series of maximum annualwater temperatures for the River Danube at Vukovar(1948–2005, with some data missing for 1952 and1992–2001), and includes a linear trend line for the studyperiod. At this station small, statistically insignificant,increase of about 0Ð017 °C per year is evident.

Figure 8. Time series of mean annual water temperatures in the RiverDrava at Donji Miholjac, with linear and polynomial trend lines

Figure 9. Time data series of the rescaled adjusted partial sums (RAPS)for the mean annual water temperature in the River Drava at Donji

Miholjac

Figure 10. Trends in mean annual water temperatures at Donji Miholjacin the two sub-periods are defined in Figure 9

Figure 12 shows the time series of maximum annualwater temperatures for the River Sava at Zagreb(1948–1998, with some data missing for the years1949–1952, 1991–1992 and 1996–1997) and at Slavon-ski Brod (1956–1998, with some data missing for1996–1997), and indicates linear trend lines for the anal-ysed periods. For both stations, the trend of increase isrelatively strong at 0Ð06 and 0Ð05 °C per year, for Zagreband Slavonski Brod, respectively.

Minimum annual water temperature

Figure 13 presents a time series of minimum annualwater temperature for the River Sava at Zagreb(1948–1998, with some data missing from the years



Figure 11. Time series of maximum annual water temperatures in theRiver Danube at Vukovar

Figure 12. Time series of maximum annual water temperature in theRiver Sava at Zagreb and Slavonski Brod

1949–1952, 1991–1992 and 1996–1997). Here the exis-tence of an increase in values is obvious. Since 1965,the River Sava at Zagreb has not frozen, but in ear-lier years freezing was frequent. The minimum averageannual water temperature for the 1948–1964 sub-periodwas about 2 °C less than in 1965–1998 sub-period.

A similar, but not identical situation, can be found forthe River Drava at Donji Miholjac. Figure 14 presents thetime series of minimum annual water temperatures forthis station. Before 1974, the water surface of the riverfroze practically every year, yet since 1974 freezing hasoccurred significantly less frequently.

Figure 13. Time series of minimum annual water temperatures in theSava River at Zagreb

Figure 14. Time series of minimum annual water temperature in the RiverDrava at Donji Miholjac

Variation along the watercourses

Figure 15 depicts a polynomial relationship betweenthe mean annual water temperature (1968–1986) andelevation for the eight water temperature stations onthe River Kupa. The correlation coefficient for thisrelationship is very high at 0Ð999. Water temperaturemeasured at stations along the Kupa watercourse is alsostrongly related to other parameters including distancefrom the river mouth (R D 0Ð994), basin area (R D 0Ð985)and mean annual discharge (R D 0Ð990). It should benoted here that the Kupari station is located about 1Ð5 kmfrom the spring source of the River Kupa. This typicalkarst spring has a mean annual discharge of about10 m3/s, and water outflows at practically a constanttemperature that varies only between 7Ð1 and 7Ð3 °C.

Figure 16 shows a polynomial relationship betweenthe mean annual water temperature and the elevationfor the four water temperature stations on the RiverDrava for 1969–1991. The correlation coefficient forthis relationship is also very high at 0Ð998, and strongrelationships are also evident between mean annualwater temperatures and distance from the river mouth(R D 0Ð996), basin area (R D 0Ð997) and mean annualdischarge (R D 0Ð999).

A similar strong polynomial relationship (R D 0Ð999)exists between mean maximum annual water temperatureand elevation of the River Drava (Figure 17) and thisparameter is also very strongly related to distance from

Figure 15. Polynomial relationship between mean annual water temper-ature and elevation of the River Kupa for the period 1968–1986 (1 -Kupari, 2 - Hrvatsko, 3 - Ladesic Draga, 4 - Kamanje, 5 - Karlovac, 6 -

Sisinec, 7 - Farkasic, 8 - Sisak)



Figure 16. Polynomial relationship between mean annual water tempera-ture and elevation of the River Drava for the period 1969–1991

the river mouth (R D 0Ð999), basin area (R D 0Ð999) andmean annual discharge (R D 0Ð992).

WATER-AIR TEMPERATURE RELATIONSHIP

Ahmadi-Nedushan et al. (2007) use stochastic approachesto relate water temperatures to air temperatures andstreamflow in the Moisie River (Canada). Their analy-sis consists of separating the water temperatures into twocomponents: a long-term seasonal component and short-term residuals. Webb et al. (2003) investigate the natureof the water-air temperature relationship, and its modera-tion by discharge, for catchments ranging in size from2Ð1 to 601 km2 in the Exe basin (Devon, UK). Theydiscover stronger relationships between water and airtemperatures for flows below median levels. The overallinfluence of flow in moderating the water-air temperaturerelationship in the catchments of the study is generallymodest, which reflects the relatively strong relationshipthat exists between water and air temperatures at alltimescales investigated (Webb et al., 2003).

The relationship between air and water temperatures inthe study area is very strong. This can be confirmed bythe fact that a polynomial regression equation betweenmean monthly water temperature values for the RiverSava at Zagreb TZw and the mean monthly air temperaturevalues for the Zagreb meteorological station TZa duringthe analysed period (1948–1998, with some data missingfrom 1949–1952, 1954, 1991–1992 and 1996–1997) is

Figure 17. Polynomial relationship between mean maximum annualwater temperature and elevation of the River Drava for the period

1969–1991

as follows:

TZw D 0Ð0118 ð T2Za C 0Ð4249 ð TZa C 4Ð2 �3�

with a very high-correlation coefficient of 0Ð975. A poly-nomial regression equation between the mean monthlywater temperature values for the Drava River at DonjiMiholjac TDMw and the mean monthly air temperaturevalues for the Osijek meteorological station TOa duringthe analysed period (1948–2005) is as follows:

TDMw D 0Ð0096 ð T2Oa C 0Ð6668 ð TOa C 2Ð5 �4�

with a correlation coefficient of 0Ð982.Figure 18 shows the annual time series of the monthly

average air temperature for Osijek meteorological stationand the water temperature of the River Drava at DonjiMiholjac during the 1948–2005 period. The differencesin the mean monthly water and air temperatures betweenthem are not statistically significant.

CONCLUSION

The RAPS established 1988 as the beginning of aconsistent trend of increase for the mean annual air andwater temperatures in the study area, as well as along thewatercourses of the four analysed rivers. Before the year1988 no consistent trends were indicated. Analysis ofwater temperature behaviour along the Kupa and Dravawatercourses shows a strong correlation with the distancefrom the river mouth, as well as with the elevation, basinarea and mean annual discharge.

It is established that a strong and direct interrela-tionship between air and water temperatures exists forthe study area. Human activities, which are often com-pletely uncontrolled and uncoordinated have resulted insignificant changes in the temperature regime, primarilyduring the low flow (Bonacci et al., 1992). During thelast 50 years, numerous regulation and drainage works,hydroelectric, hydraulic and other large structures havebeen built along the watercourse of the four study rivers,as well as in their catchment areas. These constructionshave greatly influenced the water regime, especially dur-ing low-water periods. These anthropogenic impacts are

Figure 18. Annual time series of monthly average air temperature forOsijek meteorological station and water temperature of the River Drava

at Donji Miholjac during the 1948–2005 period



probably one of the causes of water temperature changes,but the natural pattern of hot and cold years is dominant.

The main problem for the analyses made in this articleis the inconsistent nature of the various data. The fact isthat several time series have different durations, and thatthere are missing data especially during the last decadeof the 20th century, caused by military actions in partof the study area. Despite this drawback, the conclusionsdrawn in this article should be accepted as realistic andreliable for the first stage of analysis. The fact is, accurateanswers to many of the questions concerning changesin the water temperature regime of the analysed riverscannot be gained using only characteristic annual (mean,minimum and maximum) data. Some processes canbe explained measuring and analysing climatologic andhydrologic data and interactions over shorter and longertime increments. It should be stressed that continuousand automatic water temperature monitoring has to beestablished in order to collect more accurate data.

In addition, more detailed research is needed to betterexplain the changes, especially the rising of river watertemperatures over the last 20 years. This is especiallyimportant because of the increasingly frequent occurrenceof low-water flow and drought in the study area duringrecent decades. For the sustainable development andprotection of valuable analysed water resources, it is veryimportant to establish pre-requisites for the definition ofprecise causes and consequences of the above mentionedprocesses, which can be extremely harmful.

REFERENCES

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Bonacci O, Trninic D. 1991. Hydrologische, durch die Aktivitat desMenschen hervorgerufene Veranderungen im Flussgebiet der Sava beiZagreb (Man’s influence on hydrological changes on the Sava Rivernear Zagreb). Wasserwirtschaft 81(4): 171–175.

Bonacci O, Ljubenkov I. 2007. Changes in flow conveyance andimplication for flood protection, Sava River, Zagreb. HydrologicalProcesses 22(in press). DOI: 10.1002/hyp.6688.

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Webb BW, Nobilis F. 1997. Long-term perspectives on the nature ofthe air-water temperature relationship: a case study. HydrologicalProcesses 11(2): 137–147.

Webb BW, Nobilis F. 2007. Long-term changes in river temperatureand the influence of climatic and hydrological factors. HydrologicalSciences Journal 52(1): 74–85.

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Analysis of the water temperature regime of the Danube and its tributaries in Croatia