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ARIDE Assessment of the RegionalImpact of Droughts in Europe
An Electronic Atlas for Visualisation ofStream Flow Drought
Technical Report 7
M.D. Zaidman, H.G. Rees & A. Gustard
July 2000
Technical Report to the ARIDE project No.7
An Electronic Atlas for Visualisation of Stream Flow Drought Maxine Zaidman, Gwyn Rees & Alan Gustard
Supplement to Work Package 3: Drought Visualisation
Centre for Ecology and Hydrology Crowmarsh Gifford Wallingford Oxfordshire OX10 8BB UK
i
Executive Summary
This technical report documents Activities 3.1, 3.2 and 3.3 of the ARIDE Project (Assessment of
the Impact of Droughts in Europe): visualisation of stream-flow drought at a Pan-European
scale. Spatial data sets of flow exceedance at a daily time step were derived from historic gauged
daily flow data stored on the FRIEND European Water Archive. A software application was
developed to read the data sets, and to display them as on-screen images. The end product was an
electronic ‘drought atlas’, capable of displaying on-screen images of streamflow conditions over
Western and Central Europe for several drought events occurring within the last thirty years.
Firstly a methodology for deriving daily flow exceedance series for each gauging station was
developed. This included the use of ProFortran and Fortran subroutines to extract and manipulate
data from the European Water Archive database. Further programs were used to map, at each
time step, the exceedance value for each gauging station to the correct position on a 0.25o
resolution grid covering Western Europe, Scandinavia and the Iberian Peninsula. The
exceedance values for stations falling within the same grid square were averaged, so that each
was assigned a unique exceedance value ranging from null (no data), through to 100%
exceedance. Finally GIS techniques were used to convert each grid from latitude and longitude
to Lambert Azimuth projection with grid units in kilometres and a grid resolution of 22km.
The software application was developed in AVS/Express, a visualisation package. A Graphical
User Interface (GUI) was added allowing the user to control which digital images were
displayed, the appearance of those images (e.g. colour scales used). An ‘Animation Facility’
which allows the user to replay a series of images in chronological order was also incorporated
into the software. Animations may be ‘exported’ from the drought atlas as MPEG movies, and
the digital maps may be saved as postscript image files.
This technical report describes the development of both data and software application. A number
of ‘screen shots’ are presented illustrating the main features of the atlas. Three animations
exported from the atlas are also included as hard copy in the appendix. These show the ‘ebb and
flow’ of drought over the European landmass during three recent droughts: the 1976, 1990 and
1992 events.
ii
Acknowledgements The research presented in this Technical Report was carried out in the framework of the ARIDE
Project (Assessment of the Regional Impact of Droughts in Europe), supported by the European
Commission under Contract no. ENV4–CT97–0553.
The analysis was based on flow data taken from the FRIEND European Water Archive. The
authors gratefully thank and acknowledge those organisations that have contributed to the
Archive over the past two decades.
iii
Contents Page
1 Introduction 1
1.1 Background 1
1.2 Aims and Objectives 2
1.2.1 Aim of Developing a Drought Atlas 2
1.2.2 Objectives of Software Development 2
1.3 Methodology 3
1.4 Layout of the Report 5
2 Derivation of Spatial Data 6
2.1 Deriving Time Series of Daily Flow Exceedance 6
2.1.1 Method 6
2.1.2 Availability of Data 8
2.1.3 Manipulation of Data 9
2.2 Deriving Spatial Data 10
2.2.1 A Pan-European Exceedance Grid 10
2.2.2 Transformation to Lambert Azimuth Projection 10
2.2.3 Assumptions of the Method 10
3 Software Development 12
3.1 User Requirements and Functional Specification 12
3.2 Development of the Application 14
3.2.1 The Development Environment –AVS/Express 14
3.2.2 Building the Application 15
4 Software Demonstration 14
iv
5 Assessment and Conclusion 22
5.1 Appraisal of ElectrA 22
5.2 Recommendations for Future Development 23
6 References 25
Appendix 1 Summary of data presently available on the FRIEND European A1
Water Archive database
Appendix 2 Application subroutines in modular format A2
Appendix 3 Animations of drought events in Europe A4
Appendix 4 Users manual for the ElectrA software A5
1
1 Introduction
1.1 Background
Assessment of the Regional Impact of Droughts in Europe (ARIDE) is a collaborative study
funded by the European Commission and is aimed at improving current understanding of
hydrological aspects of widespread European droughts. The project is subdivided into five ‘work
packages’, each either addressing our understanding of the physical processes that influence
droughts (e.g. meteorology, hydrogeology), or developing methods for monitoring, assessing and
predicting droughts. Each work package is further subdivided into a number of specific activities
as described in the ARIDE Work Programme (Demuth (ed.), 1998).
Work Package 3, Drought Visualisation, focuses on understanding the mechanisms controlling
areal aspects of drought development in Europe. As part of Work Package 3 a study of the
spatial and temporal distribution of river droughts within Europe during the period from 1960 to
1995 was undertaken. Firstly a series of analyses of flow data stored on the FRIEND European
Water Archive (EWA) were undertaken and used to quantify variations in drought extent,
severity and growth over time. These results are presented in ARIDE Technical Report 8
(Zaidman & Rees, 2000), In parallel with the spatial analysis, visualisation techniques were used
to display the chronological sequence of drought growth and decline as animations. In this case
flow data was represented as time series grids of flow exceedance. A software application was
developed, specifically for visualising pan European drought events (an ‘electronic drought
atlas’). This technical report describes the methodologies used to derive the exceedance data sets
and documents design, development and implementation of the drought visualisation software,
ElectrA.
2
1.2 Aims and Objectives
1.2.1 Aim of Developing an ‘Electronic Atlas’ for Visualisation of Droughts
Drought is unique among atmospheric and other environmental hazards in that it creeps up
gradually on the afflicted area (Sen, 1998). Therefore, given the onset of drought conditions in
one location, a better understanding of the spatial characteristics of drought behaviour might help
us to predict to where and how the drought might spread. This would lead to improved early
warning and mitigation of droughts, and better management of integrated water resources during
drought events (the UK Drought Mitigation Working Group (UK DMWG, 1996) highlighted the
need for improved early warning of potential drought events).
Although short-term changes in flow conditions across Europe can be linked to the synoptic
weather situation in Europe and the North Atlantic, antecedent soil moisture and groundwater
conditions, coupled with geographical restraints, affect how and where drought conditions
develop in the long term. Our understanding of how droughts evolve spatially can be improved
by examining, either qualitatively or quantitatively, the spatial variation of flow conditions
during past drought events. Computerised visualisation is one method of examining spatial
variation through time. TV weather forecasts, for example, use computerised visualisations to
show the development of rainfall and pressure systems. The use of similar approaches within the
water resources industry is, however, fairly rare. Here the aim was to develop a user-friendly
software application that could display on-screen images of historic hydrological data, allowing
the spatial and chronological variation of stream flow conditions over Europe to be visualised.
This would draw upon the relatively large amount of historic flow data for Europe (currently
over 130,000 station years of data) stored on the FRIEND European Water Archive at
Wallingford. If near real-time data were used, the software would be a suitable tool for
streamflow monitoring and drought forecasting.
1.2.2 Objectives of Software
The main objective of the software application was to display how flow conditions were
distributed across Europe in a form understandable to a layman with no expertise in hydrology,
for example, as colour coded maps (red colours representing low flows and blue colours
representing regions where flows were high and so on). It essentially had had to function as an
3
‘animated atlas’ also showing how these conditions varied over time, and thus had to include a
facility for displaying a series of maps as a video or animation. A further specific objective to be
met by the application was that it should include a fully interactive graphical user interface. This
would allow the user to alter the screen appearance of the maps, for example a choice of colour
scales could be offered.
As flow conditions across a many different rivers were to be presented on screen, each having a
different mean annual discharge, the flow index displayed had to be independent of the river
regime. It was also important to indicate how flow conditions compare to those conditions
observed on other days, rather than to focus on the absolute discharge values. As it is a
dimensionless variable and straightforward in concept, flow exceedance (or flow frequency) was
an ideal choice. A further advantage was that flow exceedance could be displayed on a linear
scale ranging from 1 to 100%.
It was also important that users of the atlas should be able to use the atlas to identify regions
afflicted by drought based on their own criteria for defining the onset of drought conditions (i.e.
no arbitrary threshold should be used to predefine the drought extent). For instance if the user
was interested in the flows below the Q70 level, he/she would look at the distribution of cells in
the 70-100% range, and so on. This would allow the atlas to be used for a range of applications,
including agriculture, engineering design and public water supply design etc.
1.3 Methodology
Several intermediate stages were required to produce a working drought atlas as shown in the
flow chart (Figure 1). The first two stages related to generation of spatial data sets showing
variation in flow conditions across Europe. Firstly time series of gauged daily discharges were
retrieved from the FRIEND European Water Archive (EWA). In order to be consistent with
methods used elsewhere in the ARIDE project, a methodology of expressing flows as a
percentage flow exceedance derived using a 31-day running average method was adopted. In the
second stage a mapping procedure was implemented in which station data, for selected time
steps, were transferred to grid format.
4
Figure 1. Stages in the development of the electronic drought atlas.
The third and fourth stages involved the development of the software for displaying these data
grids. A number of possible development environments were considered including visual
programming (e.g. a stand-alone application using Visual Basic), customised GIS (e.g. an
ARCView extension) and visualisation packages (e.g. PVWave or AVS/Express applications).
Considering the aims of the project and the time / funds available, using a visualisation software
package was the most suitable approach, having two distinct advantages: sequences of digital
images can be readily displayed (unlike GIS), and the capacity for plotting data is already in
place (whereas in visual programming it would have to be designed and built). The development
of the application was divided into two distinct parts; the design and development of its
functionality (including system to read data), and the design and development of its graphical
user interface.
Automated procedure to retrieve data from the European Water Archive (EWA) and generate time series of flow
exceedance values for each gauging station
At each time step spot (station) exceedance values mapped
into a grid format
Adapt AVS/Express system to read grid data sets and link this to other AVS functionalities that allow data to be manipulated, displayed as digital maps, animated and output
to file.
Create a Graphical User Interface (GUI) in AVS/Express that will act as the ‘Front-End’ of the software, and allow the user
to control each functionality.
5
1.4 Layout of the Report
The report is presented in five sections. Following this introduction (Chapter1), the
methodologies used for data manipulation are described in Chapter 2. This includes detailed
descriptions of the method used to transform the gauged daily flow data into time series of flow
exceedance, and of the method used to map spot values into 2-D grids describing the spatial
variation of exceedance over western Europe. The development process and the functionality of
the software application are described in Chapters 3 and 4 respectively. Finally in Chapter 5
software and methodologies employed are assessed, and recommendations for improvement and
suggestions for further work are given.
6
2. Derivation of Spatial Data
2.1 Deriving Time Series of Daily Flow Exceedance
2.1.1 Method
Flow exceedance is a dimensionless index that represents the proportion of time that a specified
discharge (usually the daily mean flow) is equalled or exceeded during the period of record
(Gustard et al., 1992). A flow exceedance value derived for one catchment can be compared to
an exceedance value derived for another catchment without needing to make adjustments to
account for their different flow regimes. The exceedance for a given discharge may be
determined from the flow duration curve, which gives the duration (proportion of time) of
occurrence of the whole range of flows experienced by the river. The exceedance may also be
obtained by ranking all historic discharges according to size, determining the rank of a particular
discharge, and calculating its flow exceedance based on the proportion of flows of higher
ranking.
In Europe discharges in the summer months will generally be exceeded for a large proportion of
the record period (whilst flows in the winter period will be exceeded for a much smaller
proportion), regardless of whether the flows deviate from the average flow for that time of year.
Calculating exceedance based on all the daily flows observed during the entire period of record
year can mask many seasonal anomalies. To overcome this problem flow exceedance can be
derived on either a daily basis (i.e. if the period of record is long enough flows occurring on a
single day each year can be used) or on a seasonal basis (a subset of days are used).
In the ARIDE project seasonal exceedances were derived using a convention of 31-days,
whereby the daily exceedance was calculated from all flows that occur within a 31-day window
around the day of interest (e.g. during the 15 days proceeding and the 15 days following the day
of interest). For example the flow exceedance on 1 June would be calculated from all values
from 17 May to 16 June for each year of the period of record. In this approach flow exceedance
values are obtained by ranking all the discharges in this subset in ascending order, determining
the rank of a particular discharge, and calculating its flow exceedance based on the proportion of
7
flows of higher ranking. Provided there are no gaps in the gauged daily flow record, the
percentage flow exceedance for any day of the year (d) is given by
Ed = � �
nkn d
31%10031 �� (1)
where Ed is the flow exceedance on day d, n is the number of records years, and kd is the ranking
position of the gauged daily flow on day d.
As example, Figure 2 shows the subset of gauged daily flow values (from the period 2 June to 3
July inclusive for each year of record) used to determine the flow exceedance for 18 June 1995,
whilst Table 1 shows how the ranking procedure would be applied to this subset.
JUNE JULY 1960 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 2 3 4
1961 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 2 3 4
1962 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 2 3 4
1963 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 2 3 4
1964 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 2 3 4
��������
1992 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 2 3 4
1993 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 2 3 4
1994 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 2 3 4
1995 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 2 3 4
Figure 2. The 31-day moving-window approach; subset for 18 June
Table 1. Example of deriving flow exceedance for 18 June 1995 (rank 2 June to 3 July incl.)
Date Flow (m3/s) Rank Exceedance (%) 25 June 1964 0.3 1 99.90 03 June 1989 0.356 2 99.80 30 June 1970 0.4 3 99.70 27 June 1985 2.802 574 42.14 28 June 1985 2.802 574 42.14 03 July 1962 2.81 575 42.04 15 June 1995 27.55 990 11.20 18 June 1995 29.5 991 11.11 16 June 1995 34.3 992 11.02
8
As the flow is relatively high on 18 June 1995, it receives a ranking of 991 out of 1116 values.
The corresponding flow exceedance is low. The flow on the 18 June actually corresponds to the
11% flow percentile (the Q11 flow).
2.1.2 Availability of Data
The FRIEND European Water Archive (EWA) provides data for over 5325 gauging stations in
thirty countries. The EWA is stored on an ORACLE database system, which may be accessed
using the SQL language. A comprehensive description of the database is given by Rees (1997),
and a summary of the data presently available is given in Appendix 1. Due to the way the EWA
has evolved the data is not evenly distributed in time and space; the highest density of data is
found in Western Europe, as shown on Figure 3.
Figure 3. Distribution of gauging stations included in the FRIEND European Water Archive.
Ideally a fixed period of record should be used and stations that have too few records, or have
long record-gaps excluded. However, in order to achieve the required spatial density needed for
the atlas, it was decided to use the entire period of record when deriving daily exceedance series
for each station. The main disadvantage of this approach is that exceedance values are in fact
9
very sensitive to the period of record from which they are calculated. Where the period of record
for a gauging station is short, exceedance values may be very different than that at a nearby
gauging station where the period of record is much longer (and thus incorporates a wider range
of flows) even if flow conditions are similar at both sites. For example, if the historic flow record
for a station included data from 1930 to 1980, daily flows during the 1975/76 drought are more
likely be assigned lower exceedance values than if the station records ran from 1950 to 2000,
because the 1930’s were particularly dry.
2.1.3 Manipulation of Data
As an automated procedure was needed to access the European Water Archive ORACLE
database, download the correct data and calculate the flow exceedances for each station for each
day of interest, a proFORTRAN program (F77 with embedded SQL statements) was used. The
program had several component subroutines as follows:
1. Query the database to obtain ID number of qualifying gauging stations
2. For each station in turn
i. Query the database to obtain the appropriate gauged daily discharges
ii. Store each discharge and corresponding date in a multidimensional array
iii. For each day (from 1 to 365) in turn
a. Select (from the array) the correct set of discharges for each 31-day
window
b. Sort and rank the selected discharges
c. Calculate the exceedance value associated with each ranked position.
d. Store each exceedance and date in a second multidimensional array
iv. Output the exceedance values to data file in chronological order.
For each day an output file was produced, containing a list of stations and corresponding
exceedance values. Each set of values was then translated onto a grid, to form a spatial data set,
as described in the next section.
10
2.2 Deriving Spatial Data Sets
2.2.1 A Pan-European Exceedance Grid
A methodology to combine time series from different stations to form spatial data sets was
developed. Firstly a Fortran program was used to assign latitude and longitude co-ordinates to
each station. A separate program was used to map the location of each gauging station onto a
0.25o resolution grid covering the whole of Western Europe (from 10.5oW to 37oE, and from
34.5oN to 71oN). In some cases two or more gauging stations mapped to the same grid square.
The majority of grid squares contained no gauging stations (these areas representing seas, lakes
and ungauged regions). For any given day, the number of data points (stations) falling within
each grid square were calculated. If there were two or more data points in a grid square, the
average exceedance of those points (for that particular day) was calculated, and this value
attributed to the grid square. If there was a single data point, its exceedance value was assigned
to the whole grid square. Grid squares with no stations were assigned null values. The grid cell
values were systematically output to file as ASCII text, with a separate file for each time step.
2.2.2 Transformation to Lambert Azimuth Projection
Each grid was resampled using the ARC/INFO graphical information system (GIS) into Lambert
Azimuth projection. In Lambert Azimuth projection each cell represents an equal area on the
earth’s surface. In the radial projection (degrees) each grid square varies in area, becoming
smaller with increasing latitude. The dimension of the new grid was 22km.
2.2.3 Assumptions of the Method
Several assumptions are made in the mapping procedure. Firstly, exceedances are simply taken
as spot values, and no reference is made to the catchments that they represent. This means that
where there are two or more stations within one grid square it is assumed that the areal
contribution from each is equal. This will rarely be the case, and quite often one of two
catchments located in the same grid square will be nested inside the other. Unfortunately this
method does not identify nested catchments, nor make any special consideration for them.
Secondly, depending on catchment size and shape, a catchment may contribute to more than one
11
grid square. However using this method, only the grid square containing the gauging station will
receive an exceedance value.
12
3. Software Development
3.1 User Requirements and Functional Specification
After considering the proposed end-use of the application a list of user requirements were
identified. These relate to four categories; Platform and Memory, Functionality of the atlas
(including animation facilities and user-interface), Information Displayed and Appearance.
i. Platform and Memory
��The software should function on either a PC running Windows 95 or on a Sun
workstation running a UNIX operating system. Portability from a PC to Unix
(and vice versa) would, however, be highly advantageous.
��The software should not require large amounts of memory/processor; i.e. it
should run comfortably on a 100MHz Pentium with 8MB RAM.
ii. Functionality of the Atlas
��The software should essentially function as an electronic atlas, allowing
scaled maps of the flow exceedance distribution in Europe to be displayed on
screen.
��The system should incorporate an animation facility in which a series of maps,
selected by the user, may be displayed sequentially forming an animation or
movie.
��The system should allow the user to print coloured or black and white hard
copies of screen images.
��The atlas and animation controls should be freely accessible to the user.
��The system should incorporate a Graphical User Interface (GUI) allowing the
user access to atlas and animation controls.
��Within the GUI the user should have the opportunity to select different
options relating to the opening and closing, saving and printing of
maps/datafiles.
��Within the GUI the user should have the opportunity to change the appearance
of the images/maps produced by the atlas.
��The GUI should allow the user to control the animation facility.
13
��The user should be able to specify the period of animation (exact times for the
animation to start or stop).
��The user should be able to control the speed of animation.
��The user should be able to pause the animation.
��The user should be able to save the animation as an MPEG movie.
iii. Information Displayed
��The software should have the capability of displaying data for each day during
the 1975-1995 period.
��A system that allowed additional data to be added at a later stage would be
highly advantageous.
��The system should allow the user to access and plot time-series for individual
grid cells as desired.
��Either political or hydrologic (geographic) boundaries should be incorporated
into the flow exceedance maps.
iv. Appearance
��Each map / image should be clearly labelled with its date.
��Charts and maps will be labelled clearly and axis dimensions displayed. Each
chart / map will be given appropriate title, subtitle(s), legend and colour bar.
��On maps, coastlines should be clearly visible.
��The shade set used to colour the images should be a graduated colour scale
running from 0 to 100%.
��The system should allow the user to zoom into images.
��Titles and labels should be continuously updated throughout the running of
animation sequence.
14
3.2 Development of the Application
3.2.1 The Development Environment –AVS/Express
AVS/Express Visualisation Edition was chosen as the development environment. AVS/Express
is produced by Advanced Visual Systems, and is available for both personal computers (where it
can be opened either from windows or via DOS) and UNIX. In AVS/Express complex three-D
graphics can be displayed and manipulated (e.g. rotation, sub-sampling, colour changing) on
screen by the use of a customisable user-interface facility. The key features of AVS/Express
include a visual programming environment, an event driven object manager, visualisation
graphing and plotting functions and a graphical user interface (GUI) builder.
AVS/Express is a modular, object–oriented and hierarchical system. Users are able to construct
visualisation applications by combining software modules, each with a specific function, into
networks in which the modules interact, e.g. by passing data to one another, or by specifying
status conditions. The modules in the network are arranged in a hierarchy. Each module is
connected to a ‘parent module’ and may pass its output to one or more ‘child’ modules, or
‘feedback’ to modules of higher rank. All modules are event driven, i.e. they can be set to
activate according to the status of another module. The hierarchy controls the way the modules
interact and hence the ultimate functionality of the application as a whole. The modules are the
visual representation of sections of program code and in this way an application can be
developed without the need to use traditional procedural programming.
A large number of modules are provided with the system, ranging from the simple (such as
summing two integers) to the complex (such as taking a slice through a 3-D data set). Generally
modules provide one of three types of functionality; filtering (in which data sets are manipulated,
e.g. arithmetic or clipping data); mapping (e.g. into 2-D or 3-D space); and rendering (in which
data are transformed into pictures/graphs on the display screen). Where special functions are
required, are not included in the module library, the user is able to add modules, either in C, C++
or FORTRAN, to the library.
Modules for building or customising the Graphical User Interface are also provided. This means
that there is a large degree of flexibility regarding data input and output from the system. For
example ‘tick boxes’ and slider bars can be incorporated into the user interface.
15
3.2.2 Building the Application
In the first instance the drought atlas was developed on a UNIX platform using AVS/Express
V4.2. Additional modules were incorporated using FORTRAN 77 as the source code. Later the
system was transferred to PC, where AVS/Express V5.0 was used. The source codes for the
additional modules were rewritten using Microsoft Visual C++. Although the system was
developed according to a design plan, a certain amount of trial and error was required in order to
build some of the more complex facilities such as the animator and the colour palette options. A
number of special modules were required, including a module capable of reading and allocating
memory to the grid data.
The modules required to create the different parts of the application were grouped as macro-
modules or subroutines. Figure 4 shows the top-level network of modules, and illustrates the
connections between different subroutines macros.
Figure 4. Top-level AVS network
The macros shown include the AnimationControlMacro, the subroutines used to control the
animation facility, and the DisplayMacro, the subroutine that displays the data to screen. The
GUI for reading and storing data and displaying data was also developed using a series of
16
specialised modules from the module library, stored together within the UserInterfaceMacro. The
networks behind the individual macros are shown in Appendix 2.
17
4. Software Demonstration
In order to illustrate the functionality and appearance of ElectrA, a series of ‘screen shots’ are
presented in this section. An electronic copy of the software manual is included in Appendix 4.
Two MPEG movies, illustrating ElectrA’s animation facility, are available; these are described
in more detail in Appendix 3.
Figure 5 is a screen image of ElectrA showing its general appearance and layout. The menu bar,
containing the File, Visualisation and Help pull-down menus is located at the top of the screen.
The user-interface window is located to the left, and the map image of Europe is shown in the
right hand window. A window can be closed, minimised or set to maximum extent using the
icons in its top right hand corner.
Figure 5. Screen appearance of the ElectrA software
18
In this example data for the year 1976 has already been loaded and the atlas being used to
animate a series of drought distribution maps. The user has opened the Animation Facility
window (by default all user-interface windows appear on the left-hand side of the screen), which
can be selected via the ‘Visualisation’ pull-down menu. The window consists of three panels.
The animation options panel (upper panel) shows that the animation has been set to run from the
1st January to the 31st December, a total of 365 days. As a large number of frames are to be
animated, the speed has been set at the highest setting (lower panel). Setting the speed at its
highest setting also gives the animation a more fluid appearance. The animation is controlled
primarily by the second panel, which contains ‘Run’, ‘Pause’ and ‘Reset’ check-boxes. To start
the animation the ‘Run’ box must be activated; to stop the animation, the ‘Run’ box must be
unchecked. In this example the animation facility is running, but has been paused on the 98th day
/frame of the animation (the Run and Pause boxes are both checked). The current frame (8th
April 1976) is shown in the map window.
The map image shows the river flow conditions across Europe. On the map, each grid square
represents an area of about 500km2. Each square is coloured according to its exceedance value
on that day. In the example shown in Figure 5, a discrete scale has been used, in which each 10%
block is assigned a particular colour, ranging from blue at low exceedance through green and
yellow representing average conditions to orange/red at high exceedance. Four alternative colour
schemes are available, including a gradual scale from 1% to 100%, and gradual scales from 70%
to 100%, and from 90% to 100%. The later are useful when only drought area is of interest, and
more detail is required in the high exceedance ranges. Figure 6 illustrates how the colour scale
may be changed by selecting the ‘Settings’ option from the ‘Visualisation menu. The map
background may also be changed from the Settings window. Europe can be displayed as a
political map (currently selected), as a hydrometic map (showing the FRIEND hydrometric
regions), or as a simple coastline.
19
Figure 6. ElectrA provides a number of alternative colour scales – using a 70%-100% range
allows drought areas to be delimited more effectively.
The software allows the flow conditions on a particular day to be studied in more detail, through
its ‘Time Frame Analysis’ option under the Visualisation Menu. Figure 7, shows how this
facility may be used to visualise the flow conditions on a single day in time, in this case the 12th
February 1976 (the day and month are selected using the slider bars in the upper panel). When
the time frame facility is selected a bar chart automatically appears on screen, by default in the
lower right hand corner. The chart shows the proportion of the non-zero area of the map falling
within each of ten exceedance ranges (1%-10% exceedance, 11%-20% exceedance and so on).
20
Figure 7. Analysis of the spatial distribution of flow conditions at a single time frame.
If a particular region / grid square is of particular interest it can be selected using the mouse
(instructions are given in the software). The co-ordinates and exact exceedance value of the cell
are returned in the lower panel (Figure 8). A time series plot can be displayed by checking the
‘Time Series Plot’ box as shown in Figure 8.
21
Figure 8. Selecting a grid cell and displaying the long-term variation in flow conditions at that
point.
The new plot shows the variation of flow conditions throughout the current year at the selected
grid cell, and allows the spot exceedance to be placed in context of long-term variations. A
summary of the characteristics of the time series is also given, for instance the range of
exceedance values recorded and the annual average exceedance are given.
Other features of ElectrA include the printing facility, and the trouble-shooting facility, which
may be accessed via the ‘File’ and ‘Help’ pull-down menus respectively. Using the print facility
screen images may be saved to file, as MPEG images or directly to printer.
22
5. Assessment and Conclusion
5.1 Appraisal of ElectrA
In appraisal of the ElectrA software the user requirements discussed in Chapter 3 must be
considered. The user requirements were classified into four categories; Platform / Memory,
Functionality, Information and Appearance. Table 2 compares the requirements and performance
of ElectrA, and indicates where these requirements were met or surpassed.
Table 2. Comparison of user requirements and ElectrA end product
Category Were requirements
met by ElectrA ?
Were requirements
surpassed ?
Comments
1) Platform Yes
2) Functionality Yes Yes �� The user was able to switch
between different functionalities.
�� The user was able to display the
time series for a selected location
3) Information No �� Presently accesses data for 1975-
77, 1983/84, 1988-90, 1992-95
only (rather than 1975-1995
period)
�� Loading mechanism very slow
4) Appearance Some requirements in
this category were
not met
Some requirements in
this category were
surpassed
�� Loading mechanism very slow
Map Appearance was
unsatisfactory due to the poor
resolution of the country and
coastline boundaries
�� A range of additional colour scales
were provided, including a discrete
scale from 0-100%, and scales
between 70-100% and 90-100%.
In general ElectrA fulfilled the user requirements, though there were two problem areas. These
were 1) the mechanism for loading data into ElectrA and 2) the quality of coastline and country
23
boundaries. The main problem with the loading mechanism is the time taken to load data for a
single year. In the present system all 365 data sets (one for each day) are read in to the system
memory, and stored there for later use. Depending on the PC specification this takes between 40
seconds and 4 minutes! An additional shortcoming is that a reduced range of data sets is
available. This resulted from an effort to save space – 30 x 365 data sets takes up a large amount
of ROM.
The second problem relates to the appearance of the drought maps. The polygons defining the
coastal and political borders are of poor resolution, with some having straight edges. The co-
ordinates of these polygons were derived from ARC/INFO shapefiles. A special module,
obtained from the AVS Users Group module library, was used to translate these co-ordinates into
a series of points on the maps, which were then joined. Some modification is required to ensure
that the module plots all co-ordinate points; the poor resolution results from some points being
omitted.
5.2 Conclusions and Recommendations for Future Development
In its present form the drought visualisation atlas, ElectrA, could be used in the water resource
industry, as a tool for examining historic flow data.
However several improvements could be made both in terms of atlas functionality and data
quality. Firstly the application itself would benefit from improved mechanisms for loading data,
and for displaying the country/coastal boundaries. This development would probably require
about twenty additional man-hours. Secondly the quality of the grid data sets was relatively poor,
due to a lack of available data for many areas across Europe, particularly for southern and
eastern regions. A further limitation is that the data is presented at a resolution of 22km, which is
too coarse for examining drought on a basin or regional basis. Until such a time that the spatial
density of gauging stations included in the European Water Archive is improved, it would be
advantageous to adapt the atlas to consider drought at the regional rather than the pan-European
scale.
ElectrA would also benefit from development with AVS/Express Developer Addition. The
Developer Addition includes more versatile graphing and plotting facilities, and an enhanced
GUI builder. Applications can be saved as stand-alone executables, and so can be used without
installing AVS/Express. An executable version is advantageous if ElectrA is to be widely
24
disseminated within the scientific community, and is a necessity for any future commercial
dissemination.
Characterisation of past drought events is, however, of little operational use unless definitive
patterns in the development of droughts can be identified, and used to predict future spatial
development of droughts at a near real time scale.
25
6. References
Demuth, S. (ed.) 1998. Work Programme for the ARIDE Project. Report to the European
Commission.
Hisdal, H., Tallaksen, L.M., Peters, L., van Lanen, Stahl, K.& Demuth, S. 1999. Drought Event
Definition. ARIDE Technical Report no 6.
Gustard, A., Bullock, A. & Dixon, J.M. 1992. Low Flow Studies in the UK. Institute of
Hydrology Report 108, Wallingford. 88pp.
Rees, H.G. 1997. The FRIEND European Water Archive. In: Oberlin. G. and Desbos E. (eds.)
1997. FRIEND, Flow Regimes from International Experimental and Network Data. Third
Report: 1994:1997. UNESCO-Cemagref, 300pp.
Sen, Z. 1998. Probabilistic formulation of spatio-temporal drought pattern. Theoretical Applied
Climatology, 61, 197-206.
UK Drought Mitigation Working Group (UK DMWG, 1996)
Zaidman, M.D. & Rees, H.G. 2000. Spatial Patterns of Streamflow Drought in Western Europe
1960-1995. Technical Report to the ARIDE Project, no 8.
26
Blank
A1
Appendix 1 Summary of the FRIEND European Water Archive Database
Table A1. Number of gauging stations and station years of data per country
Country Number of
Stations
No Stations
with Daily
Flow Records
Earliest
Record
Latest
Record
Station
Years
Average
Record
Length Austria 139 139 1922 1996 4520 33
Belarus 40 33 1919 1995 1383 42
Belgium 80 74 1929 1992 803 11
Bulgaria 3 3 1978 1986 27 9
Czech Rep. 34 27 1887 1993 1468 54
Denmark 43 35 1917 1997 2115 60
Finland 71 68 1847 1997 3674 54
France 1476 1333 1863 1992 29734 22
Germany 717 625 1884 1998 22918 37
Greece 2 2 1978 1980 6 3
Hungary 26 25 1935 1996 825 33
Iceland 8 8 1932 1994 386 48
Ireland 130 77 1940 1997 1908 25
Italy 252 252 1925 1990 3969 16
Netherlands 30 25 1901 1994 581 23
Norway 213 204 1871 1998 7756 38
Poland 61 29 1955 1992 738 25
Portugal 73 73 1920 1994 1092 15
Romania 35 33 1838 1990 1155 35
Russia 217 146 1928 1995 6094 42
Slovakia 23 23 1930 1992 1441 63
Slovenia 12 12 1945 1990 300 25
Spain 239 239 1912 1989 3317 14
Sweden 71 66 1907 1992 2583 39
Switzerland 132 75 1904 1992 2775 37
Turkey 12 12 1958 1991 201 17
UK 1112 1014 1879 1998 29961 30
Ukraine 67 58 1960 1990 1798 31
Yugoslavia 5 5 1978 1990 63 13
SUMMARY 5325 4715 1838 1998 133591 28
A2
Appendix 2 Subroutines expressed in modular format
Figure A1 Module Network for the User-interface subroutine
Figure A2 Module Network for the Animation subroutine
A3
Figure A3. Module Network for the Image Display subroutines
A4
Appendix 3 ElectrA Movies
Three ElectrA movies are available as hard copy, and can be obtained from the authors of this
report.
Movie 1
1976.mpg
Variation in streamflow conditions across Europe between 1st August 1976 and 1 October 1976.
Movie 2
1990.mpg
Variation in streamflow conditions across Europe between 1st July 1990 and 1 September 1990.
Movie 3
1992.mpg
Variation in streamflow conditions across Europe between 1 August 1992 to 31 August 1992.
A5
Appendix 4 User Guide for the ElectrA software
ElectrA
An Electronic Atlas for Visualisation of Streamflow Drought
User Guide
M.D. Zaidman Centre for Ecology and Hydrology Maclean Building Crowmarsh Gifford Wallingford Oxon OX10 8BB August 2000
A6
Preface This guide is intended to provide only a brief reference manual to the ElectrA software, detailing
the main functions and pitfalls.
ElectrA was developed at the Centre for Ecology and Hydrology Wallingford (formerly Institute
of Hydrology) to meet the requirements of the Assessment of the Regional Impact of Droughts in
Europe (ARIDE) project. ARIDE is a collaborative study funded by the European Commission
(under contract no. ENV4–CT97–0553).
ElectrA is a user-friendly software application, which can run on any PC to which AVS/Express
has been installed. It can be used to display digital maps showing Pan-European river conditions
on any day over the last thirty years, and to isolate regions showing drought characteristics. The
digital maps are saved within the software, so that no data entry is required. A print facility
allows the maps to be printed to file. ElectrA can also be used to create animations from these
maps, which can be viewed within the software, or saved for external use as MPEG or AVI
movies.
A7
Contents Page 1. Starting the application A8 2. Selecting the data (year) for display in ElectrA A8 3. Visualising Data A9 4. Controlling the appearance of the digital maps A11 5. Creating an animation from a sequence of digital maps A14 6. Creating an MPEG movie from a sequence of digital maps A16 7. Printing digital maps to file A18 8. Using the Help Facility A19 9 Quitting the application A20
A8
1. Starting the application To start the application 1. Double click on the ‘Express’ icon Two windows will then appear on screen; the ElectrA task bar and the map window. The task bar contains three pull down menus; ‘File’, used for handling data, printing data to file and quitting the application, ‘Visualisation’, used for controlling the map display and creating animations, and ‘Help’ which is used to access the trouble-shooting guide. 2. Selecting the data (year) for display in ElectrA Only one data set (corresponding to a single year) may be accessed at any time. To load data for the desired year 1. Select File from the menu bar 2. Select the Open Data File option from the drop down menu. The Load Data dialogue now appears (Figure 1).
Figure 1. Using the Load Data dialogue to load data into ElectrA
A9
3. Select the desired year from the list, using the scroll-bar to scroll down the list if necessary. 4. Click on the LOAD DATA button ElectrA will now load the appropriate data files, a two minute operation. During this time the user will be unable to make any selections, or use the cancel and ok buttons. Once loading is complete 5. Select OK to exit the Load Data dialogue. 6. The Cancel button may also be used the exit from the Load Data dialogue. 3. Visualising Data To display a digital map showing the Pan-European variation in river flow (exceedance) for a particular day 1. Select Visualisation from the menu bar 2. Select the Time Frame / Time Series Analysis option from the drop down menu The Time Frame/ Time Series dialogue now appears on the left-hand side of the screen as shown in Figure 2.
Figure 2. Using the Time Frame / Time Series dialogue to visualise daily data.
A10
3. Select the desired day, and month using the slider bars in the upper panel. These tell ElectrA
which data to display. 4. Click the Update View check box, which is located immediately below the slider bars. ElectrA will now display a map showing the flow exceedance at location on the map. Ungauged areas are left blank (white). A bar chart showing the spread of the exceedance values will also appear. Steps 3 and 4 may be repeated in order to visualise flow conditions on additional days. The map may be queried. In order to query the map 5. Check the Read Instructions box. This will display a new window, giving more instructions
on map query (to exit the new dialogue select OK). 6. Use the mouse to point to the desired location. Hold down the left mouse button and press
the control (Ctrl) key. The location is now selected. Its co-ordinates and exceedance values are displayed at the bottom of the Time Frame dialogue window. To display the time series for the selected location 7. Check the Select Time Series Plot box. A time series plot will now replace the bar chart. A summary table also appears on screen.
Figure 3. Using the Time Frame / Time Series dialogue to display the time series for a selected
location on the digital map.
A11
To revert back to the bar chart 8. Un-check the Select Time Series Plot box. When visualisation is complete uncheck the Update View box. 4. Controlling the appearance of the digital maps ElectrA allows both the background (boundaries) and the colour scale used to plot the data to be changed. Changing the Colour Scale: 1. Select Visualisation from the menu bar 2. Select the Settings option from the drop down menu The Settings dialogue now appears on the left-hand side of the screen (Figure 4).
Figure 4. Using the Settings dialogue to alter the colour scale used when displaying the
data.
A12
3. Select one of the options from the Colour Options Box – the colour scale will adjust automatically.
4. If the ‘Isolines’ option is selected, enter appropriate values in the Number of Isolines and Lowest Contour boxes (see Table 1).
The different colour options are described in Table 1. Different colour schemes are also illustrated in Figures 3, 4 and 5.
Figure 5. Changing the colour scheme to a gradual scale.
A13
Table 1. Colour options available for plotting the data.
Colour Option Description
0-100 % range, linear scale. A linear scale used with a ‘rainbow’ palette, from blue (low flow exceedance) through red (high flow exceedance)
70–100 % range, linear scale. A linear scale starting at 70% exceedance (green), moving though to 100% exceedance (red/purple). Areas where the flow exceedance falls below 70% are not coloured.
90–100 % range, linear scale. A linear scale starting at 90% exceedance (green), moving though to 100% exceedance (red/purple). Areas where the flow exceedance falls below 90% are not coloured.
0 – 100 % range, discrete scale The scale is divided evenly into 10 discrete units (e.g. 0-10%, 11-20% and so on to 91-100%). Each unit is assigned a distinct colour.
Isolines The map is displayed as a series of isolines. The user can select how many isolines should be used, and the value of the lowest isoline (this must be at least 70% exceedance).
Changing the background: 1. Select Visualisation from the menu bar 2. Select the Settings option from the drop down menu
The Settings dialogue now appears on the left-hand side of the screen (Figure 6). 3. Select one of the options from the Background Options Box – the background scale will
adjust automatically.
There are three different background options: Political Boundaries, Hydrometric Boundaries, and European Coastline: ��If the Political Boundaries option is selected the European coastline and country borders are
displayed as a background to the map (e.g. as in Figure 5). ��If the Hydrometric Boundaries option is selected the FRIEND hydrometric region boundaries
are displayed (including coastlines) as a background to the map. ��If the European Coastline option is selected, only the coastline is displayed (Figure 6).
A14
Note that the software allows only one option to be displayed at a time (i.e. the Political option automatically becomes deselected as the Hydrometric option is selected and so on).
Figure 6. Changing the background option – in this example the European Coastline option has been selected. 5. Creating an animation from a sequence of digital maps ElectrA can be used to playback animations showing how the flow conditions change over a number of days, weeks or months. The maximum number of days that may be included in each animation is 365 (i.e. a complete year). Animations cannot contain the days from different calendar days. To display an animation showing the spatial variation in river flow (exceedance) over a selected time period 1. Select Visualisation from the menu bar 2. Select the Animation Facility option from the drop down menu
A15
The Animation Facility dialogue now appears on the left-hand side of the screen (Figure 7). The dialogue window contains three panels; the Animation Options Panel, the Animation Control Panel and the Animation Speed panel. To select the time period of which the animation is to run 3. Select the desired start day, and start month using the appropriate slider bars in the
Animation Options Panel (e.g. to start the animation on the 15 of March, set the day slider bar to 15, and the month slider bar to 3).
Figure 7. Using the Animation Facility to create Animations in ElectrA 4. Select the desired end day and month using the appropriate slider bars in the Animation
Options Panel. Make sure that the end point of the animation is set to a later date than the starting point.
5. The start and end dates are given a frame number, representing the position in the year (e.g. if 15 March is selected the position in the year is 74). Check that these values have appeared in dialogue boxes located in the Animation Control Panel. It may be necessary to re-select dates if the initial choice was not registered.
Note that the slider bar system allows dates such as 30th February to be selected. These dates are automatically transformed – in this case to the 2nd March (position 61).
A16
To run / control the animation 6. Set the animation speed using the slider bar in the Animation Speed panel. Speed level 1 is
the slowest speed, and speed level 10 the fastest. For fluidity of animation the speed level should be set between 7 and 10. The lower speed levels are appropriate for slow-motion animations.
7. Check the Reset box in the Animation control panel (the Reset box automatically resets to unchecked).
8. Check the Run box The animation should now be in progress. The speed of the animation can be changed at any point without stopping or pausing the animation. If the reset box is selected while the animation is in progress, the animation will automatically start again. To pause the animation 9. Check the Pause box. Uncheck the box to unpause. To stop the animation 10. To stop the animation click on and uncheck the Run box. 6. Creating an MPEG movie from a sequence of digital maps ElectrA can be used to write MPEG or AVI movies using a sequence of digital maps. The maximum number of days that may be included in an MPEG animation is 365 (i.e. a complete year), and days from different calendar days cannot be used. To create an MPEG animation 1. Select File from the menu bar 2. Select the Print option from the drop down menu 3. Select from the second drop down menu The MPEG Movie dialogue now appears on the right hand side of the screen (Figure 8). The MPEG facility can be used simultaneously with the visualisation facilities. The MPEG facility works by capturing the current map image and storing it in memory. If the ElectrA animation facility is used the MPEG facility can be used to record the entire sequence. Contrarily, if a non-chronological sequence is required, the MPEG facility can be used to capture a series of individual maps. When the desired sequence of maps has been recorded, the sequence may be played back, and or saved to file.
A17
Figure 8. Using the Create MPEG MovieFacility To capture a view 4. In the Capture Control panel set the mode to ‘Capture from View’ 5. In the Capture Control panel set the Capture Mode to ‘Memory’ 6. Click on the Record Button in the Capture Control View 7. Change the current view (using either the Time Frame Facility or the Animation Facility) 8. Record the new view using the Record Button. To delete a view from memory 9. Click on the Delete button in the Capture Control Panel. 10. The entire recording may be purged from the memory by using the Clear button. To playback a completed movie from memory 11. In the Capture Control panel set the mode to ‘Playback to View’ 12. In the Playback Control panel select ‘once’ from the Run option box - the playback can also
be set to cycle, or bounce (playback forwards then in reverse). 13. Set the Delay slider bar to either 0 or 1 – this sets a 0 / 1 second delay between subsequent
views on playback. Set the delay to 2 – 5 to playback in slow motion. 14. Use the playback control icons to control the movie (run, step forward though, fast forward,
rewind or stop.
A18
To save the movie to file 15. In the Movie controls panel set the mode to either MPEG or AVI 16. Enter a filename in the filename dialogue box, or use the browse button to select a
file/directory. 17. Click the Generate Movie button to save the movie to file. 7. Printing digital maps to file Any map produced in ElectrA can be printed to either a colour or black and white postscript file. To create a postscript file from the current map 1. Select File from the menu bar 2. Select the Print option from the drop down menu 3. Select Print to file from the second drop down menu The Print to file dialogue now appears on the right-hand side of the screen (Figure 9).
Figure 9. Printing a map to file.
A19
4. In the Paper Options panel, select an orientation; either portrait or landscape 5. In the Paper Options panel, set the paper size option to A4. 6. Select a filename, or use the Browse button to choose the directory/filename 7. Click on the ‘Create output file’ button to save the file. 8. Using the Help Facility The help facility may be used for ‘trouble-shooting’ some common problems such as with loading data or using the animation facility. To start the Help Facility 1. Select Help from the menu bar 2. Select the Trouble-shooting option from the drop down menu The Trouble Shooting dialogue should now appear on the left-hand side of the screen as shown in Figure 10.
Figure 10. The Trouble-shooting dialogue
A20
The trouble-shooting dialogue allows the user to select certain commonly asked questions, and supplies one or more possible solutions.
3. Select the query that most fits the description of the problem Suggestions appear in the Possible Solutions box as shown in Figure 10. 4. To quit the trouble-shooting dialogue use the OK button 9. Quitting ElectrA To exit from the ElectrA software 5. Select File from the menu bar 6. Select the Exit option from the drop down menu 7. Select OK on the confirmation dialogue.
Figure 11. Exiting the ElectrA system.
