Model-based assessment of European water resources and hydrology in the face of global change

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EuroWasser
Model-based assessment
of European water resources and hydrology
in the face of global change
Bernhard Lehner, Thomas Henrichs, Petra Döll, Joseph Alcamo
Center for Environmental Systems Research
University of Kassel
December 2001

The Kassel World Water Series:
Report No 1 – A Digital Global Map of Irrigated Areas
Report No 2 – World Water in 2025
Report No 3 – Water Use in Semi-Arid North-Eastern Brazil
Report No 4 – A Digital Global Map of Irrigated Areas (Update)
Report No 5 – EuroWasser
EuroWasser
Model-based assessment of European water resources
and hydrology in the face of global change.
Kassel World Water Series. Report Number 5
Report A0104, December 2001
Center for Environmental Systems Research,
University of Kassel, 34109 Kassel, Germany
Tel. 0561 804 3266, Fax.0561 804 3176
Internet: http://www.usf.uni-kassel.de
Please cite as:
“Lehner, B., Henrichs, T., Döll, P., Alcamo, J. (2001): EuroWasser – Model-based assessment of European water
resources and hydrology in the face of global change. Kassel World Water Series 5, Center for Environmental
Systems Research, University of Kassel, Kurt-Wolters-Strasse 3, 34109 Kassel, Germany.”

EuroWasser – Model-based assessment of European water resources and hydrology in the face of global change
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EuroWasser
Model-based assessment of European water resources and hydrology
in the face of global change
Bernhard Lehner, Thomas Henrichs, Petra Döll, Joseph Alcamo
Executive Summary
In this report we assess the possible impact of climate change on Europe’s water resources. We also
include the complicating factor of growing water withdrawals and their influence on water stress.
Since there is no standard yardstick to measure these impacts, we use the concept of “critical
regions”, meaning regions where the extent of changes to water resources (according to different
measures) is larger than in other European regions. The thinking behind this concept is that the
regions facing the most rapid changes (in the direction of higher risk) may have to devise the most
drastic adaptation measures. Conversely, regions with slower changes may be able to gradually, and
without special effort, adapt to the changes in their water resources.
As the basic spatial unit of our analysis we take the river basin and grid cell because water
withdrawals, availability, or drought and flood frequencies cannot, in our opinion, be meaningfully
averaged over larger scales like countries. Within each of the approximately 550 first order river
basins and 6500 grid cells making up Europe, we estimate several measures of changes in water
resources because it is unclear which measure is best suited for assessing impacts on society and
ecosystems. Indeed, an urgent task for the research community is to identify relevant and measurable
indicators of impact. This task requires multi-disciplinary studies of the vulnerability of society to
changes in water resources, and such studies must in particular include social scientists who up to
now have played only a small role in water resource studies. Despite the challenge of this task, it
needs to be done.
As one measure of changes in water resources we examine the change in “water stress” –
here taken as an indicator of the pressure put on water resources by water withdrawals. We show that
today’s severe water stress regions in Europe include not only expected areas such as arid Southern
Europe, but also heavily populated watersheds of North-Western and South-Eastern Europe because
of their high water withdrawals. Under future changes in population, economy, and climate change
we shown that Eastern Europe will be an especially critical region for water stress because of the
sharp increase in water withdrawals for households and industry, but also because of climate-related
decreases in water availability. As compared to other regions, the pressure on aquatic ecosystems may
increase faster, and the competition between water users may be greater. The need for intensive river
basin management is likely to increase.
Another measure of change is the change in the frequency of drought. The critical drought
regions (defined as a decrease in the return period of the current 100-year drought to 50 years or less)
include much of Southern Europe and parts of Central Europe. In these calculations the increase in
water consumption in the domestic and industry sectors again play an important role, especially in
South-Eastern Europe. During periodic dry spells, this water consumption will deplete river discharge
to a level below a critical reference flow. Drought planning in these critical regions may need to be
revised in the light of these impacts and additional adaptive measures may be needed.
Consolidating the results for water stress and drought frequencies, South-Eastern Europe
might be the area with the greatest increase in pressure on its water resources in the coming decades.
Here large areas fall under the critical regions definition regarding both water stress and drought
frequencies, in total accounting for about a quarter of Europe’s land area. This region might require
the highest degree of adaptive measures to ensure adequate water supply and protection of aquatic
ecosystems.
Future changes in the occurrence of low flows and droughts may also affect the output of
hydroelectric power plants. To address this issue we compute both an indirect measure of this impact,
namely the change in the gross hydropower potential (i.e. the potential if all runoff at all locations
were to be transformed into energy) and a more realistic measure, namely the developed hydropower
potential of current hydroelectric facilities. For the latter analysis we assume that most of Europe’s
future hydroelectricity will be generated at current hydroelectric sites because they are already good
sites, and because it is difficult to develop new sites in Europe. Under these assumptions, the critical
regions (defined as where the developed potential of hydroelectric facilities will drop by 25% or more)

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will be similar to the critical regions for droughts of Southern and South-Eastern Europe noted above.
But not all countries are equally affected because some are more reliant on hydroelectricity than
others. Of the 40 European countries investigated, 14 will experience a decline of more than 25% in
developed hydropower potential. Nine of these countries are in Eastern Europe and they may be
particularly affected by the decrease in hydroelectric potential because they are undergoing a rapid
increase in the demand for electricity.
Although we emphasize the negative impacts of climate change, it is also notable that 15% of
Europe will have decreasing water stress under the long-term scenario investigated in this study.
Where water stress decreases, water quality may improve (depending on the degree of wastewater
treatment and many other factors), and aquatic ecosystems and biodiversity may recover. Also,
according to this scenario, the current 100-year drought will occur less frequently in approximately
half of Europe’s land area, implying less frequent water shortages. In addition, the potential for
generating hydroelectricity will increase in about the same areas, along with its evident economic
benefits.But the above benefits have an important caveat – although increasing precipitation could
bring positive effects, it could also bring more intense and frequent floods. Critical flood regions
(defined as a decrease in the return period of the current 100-year flood to 50 years or less) include
much of Northern Europe, and smaller parts of Central and Southern Europe. These regions cover
many of the same areas that may benefit from decreased occurrence of drought. Here new strategies
may be needed to prevent an increase in damaging river flooding. Preliminary modeling results
indicate that some parts of Southern and Central Europe may even be in a special category where
both droughts and floods become more frequent, e.g. the Wisla basin in Poland. This may be due to a
change in the seasonal variability of precipitation and temperature in these areas, but the results are
still very preliminary.
Finally, we compare critical flood regions with critical drought regions. Here the two sides of
the climate change coin become evident. Critical regions of either floods or droughts (or both) cover a
total of two-thirds of Europe’s land area. This result suggests that adaptation to more frequent
extreme climatic events should be a major concern of European water resources management.
But what should the adaptation measures be? The long list of possibilities can be clustered
into two categories: “demand side” measures that aim to reduce exposure to the impacts of climate
change, and “supply side” measures in which actions are taken to directly counteract these impacts.
An example of a demand side measure is the reduction of water use through conservation or through
changes in lifestyle or economic activity, which reduces the dependence of society on large volumes of
water during periodic water shortages. Another demand side measure is reducing society’s exposure
to flooding by prohibiting development in flood plains.
An example of a supply side measure is counteracting more frequent or intense droughts by
improving reservoir management or altering water distribution systems. Another supply side example
is adapting to more frequent floods by creating natural inundation areas or by building dikes. These
are just a few of the many adaptive measures available to European water managers in the face of
increasing impacts of climate change.
The selection of these measures will depend on the type of new risks, the current adaptive
measures being taken, the costs of new measures, the availability of land, and many other factors.
Since these and other factors are mainly specific to the country and river basin, it is appropriate to
evaluate these measures on these scales.
Yet although action should be taken on the national and river basin level, some intervention is
also justified on the European Union level because of the large total European area that may
experience either more frequent droughts or floods. It is also consistent with the findings of this study
that droughts or floods could occur more often in different parts of Europe within a relatively short
time of each other – Among other impacts, this could lead to the overtaxing of European emergency
relief services. It is also conceivable that the financial burdens of dealing with two catastrophes within
a short time span could lead to cascading financial problems between the tightly-knit economies of
Europe. In any event, we recommend that the European Union review the adequacy of its planning for
coping with water-related catastrophes in the face of climate change.
In conclusion, this study shows that climate change will have mixed positive and negative
effects on water resources in different parts of Europe, but that we should be especially alert to where
it may cause new risks and require new adaptive strategies.

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Table of Contents
1INTRODUCTION _______________________________________________________________ 1-1
2THE GLOBAL INTEGRATED WATER MODEL WATERGAP 2.1 _______________________ 2-1
2.1 INTRODUCTION ______________________________________________________________ 2-1
2.2 MODEL DESCRIPTION__________________________________________________________ 2-2
2.2.1 Spatial base data__________________________________________________________ 2-3
2.2.2 Climate input ____________________________________________________________ 2-3
2.2.3 The Global Water Use Model ________________________________________________ 2-4
2.2.4 Global Hydrology Model____________________________________________________ 2-8
2.3 CONCLUSIONS ______________________________________________________________ 2-17
2.4 REFERENCES _______________________________________________________________ 2-18
3PERFORMANCE OF WATERGAP AS COMPARED TO MESOSCALE MODELS: A CASE
STUDY FOR THE ELBE AND ODER BASINS________________________________________ 3-1
3.1 INTRODUCTION ______________________________________________________________ 3-1
3.2 OVERVIEW OF THE APPLIED MODELS______________________________________________ 3-2
3.2.1 WaterGAP (GhK) _________________________________________________________ 3-2
3.2.2 ARC/EGMO (PIK)_________________________________________________________ 3-3
3.2.3 GESIMA/SEWAB (GKSS) ___________________________________________________ 3-3
3.3 RESULTS ____________________________________________________________________ 3-3
3.3.1 Spatial and temporal model comparisons _______________________________________ 3-4
3.3.2 Macroscale modeling using mesoscale precipitation data ___________________________ 3-9
3.4 CONCLUSIONS ______________________________________________________________ 3-10
3.5 REFERENCES _______________________________________________________________ 3-11
4BASELINE-A: A REFERENCE SCENARIO OF GLOBAL CHANGE _____________________ 4-1
4.1 INTRODUCTION ______________________________________________________________ 4-1
4.2 THE BASELINE-A SCENARIO ____________________________________________________ 4-2
4.3 CLIMATE CHANGE ____________________________________________________________ 4-2
4.4 SOCIO -ECONOMIC DRIVING FORCES _______________________________________________ 4-4
4.4.1 Population ______________________________________________________________ 4-5
4.4.2 Income _________________________________________________________________ 4-6
4.4.3 Electricity Production ______________________________________________________ 4-6
4.4.4 Irrigated Areas ___________________________________________________________ 4-7
4.4.5 Structural Change_________________________________________________________ 4-7
4.4.6 Technological Change______________________________________________________ 4-8
4.5 CONCLUSIONS _______________________________________________________________ 4-8
4.6 REFERENCES ________________________________________________________________ 4-8
5EUROPE’S WATER STRESS TODAY AND IN THE FUTURE___________________________ 5-1
5.1 INTRODUCTION ______________________________________________________________ 5-1
5.2 EUROPE’S WATER STRESS TODAY_________________________________________________ 5-2
5.2.1 Water availability _________________________________________________________ 5-2
5.2.2 Water withdrawals ________________________________________________________ 5-3
5.2.3 Water stress______________________________________________________________ 5-3
5.3 EUROPE’S WATER STRESS IN THE FUTURE __________________________________________ 5-4
5.3.1 Water availability _________________________________________________________ 5-4
5.3.2 Water withdrawals ________________________________________________________ 5-6
5.3.3 Water stress______________________________________________________________ 5-7
5.4 CONCLUSIONS ______________________________________________________________ 5-10
5.5 REFERENCES _______________________________________________________________ 5-11

EuroWasser – Model-based assessment of European water resources and hydrology in the face of global change
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6EUROPE’S FLOODS TODAY AND IN THE FUTURE__________________________________ 6-1
6.1 INTRODUCTION ______________________________________________________________ 6-1
6.2 METHODOLOGY ______________________________________________________________ 6-2
6.2.1 General overview of flood and flood frequency calculations _________________________ 6-2
6.2.2 Data limitations __________________________________________________________ 6-3
6.2.3 The WaterGAP 2.1 model ___________________________________________________ 6-4
6.2.4 Flood calculations with WaterGAP ____________________________________________ 6-5
6.2.5 Evaluation of WaterGAP regarding flood assessments _____________________________ 6-6
6.3 RESULTS ____________________________________________________________________ 6-9
6.4 CONCLUSIONS ______________________________________________________________ 6-14
6.5 REFERENCES _______________________________________________________________ 6-15
7EUROPE’S DROUGHTS TODAY AND IN THE FUTURE ______________________________ 7-1
7.1 INTRODUCTION ______________________________________________________________ 7-1
7.2 METHODOLOGY ______________________________________________________________ 7-2
7.2.1 General overview of low flow and drought calculations_____________________________ 7-2
7.2.2 The WaterGAP 2.1 model ___________________________________________________ 7-4
7.2.3 Drought calculations with WaterGAP __________________________________________ 7-5
7.2.4 Evaluation of WaterGAP regarding drought assessments____________________________ 7-6
7.3 RESULTS ___________________________________________________________________ 7-10
7.4 CONCLUSIONS ______________________________________________________________ 7-15
7.5 REFERENCES _______________________________________________________________ 7-16
8EUROPE’S HYDROPOWER POTENTIAL TODAY AND IN THE FUTURE _______________ 8-1
8.1 INTRODUCTION ______________________________________________________________ 8-1
8.2 GENERAL OVERVIEW OF HYDROPOWER UTILIZATION IN EUROPE________________________ 8-2
8.2.1 Classification of hydroelectric power stations ____________________________________ 8-3
8.2.2 Today’s hydropower utilization in Europe_______________________________________ 8-3
8.2.3 Perspectives of hydropower development independent from climate change______________ 8-4
8.3 GENERAL METHODOLOGY ______________________________________________________ 8-5
8.3.1 Types of hydropower potentials _______________________________________________ 8-5
8.3.2 The WaterGAP 2.1 model ___________________________________________________ 8-6
8.4 GROSS HYDROPOWER POTENTIAL ________________________________________________ 8-7
8.4.1 Methodology _____________________________________________________________ 8-7
8.4.2 Calculation of the gross hydropower potential with WaterGAP _______________________ 8-8
8.4.3 Results _________________________________________________________________ 8-8
8.5 DEVELOPED HYDROPOWER POTENTIAL ___________________________________________ 8-10
8.5.1 Methodology ____________________________________________________________ 8-10
8.5.2 Calculation of the developed hydropower potential with WaterGAP___________________ 8-11
8.5.3 Results ________________________________________________________________ 8-12
8.6 CONCLUSIONS ______________________________________________________________ 8-16
8.7 REFERENCES _______________________________________________________________ 8-18
9SUMMING UP EUROWASSER: AN INTEGRATED ASSESSMENT OF CLIMATE CHANGE
IMPACTS ON EUROPE’S WATER RESOURCES _____________________________________ 9-1
9.1 INTRODUCTION ______________________________________________________________ 9-1
9.2 WHAT IS THE APPROACH OF THE PROJECT?_________________________________________ 9-2
9.3 WHAT IS THE CURRENT SITUATION OF WATER STRESS IN EUROPE’S RIVERS?_______________ 9-3
9.4 HOW WILL WATER STRESS CHANGE IN THE FUTURE?__________________________________ 9-5
9.4.1 Changes in water withdrawals________________________________________________ 9-5
9.4.2 Changes in water availability ________________________________________________ 9-6
9.4.3 Changes in water stress_____________________________________________________ 9-7
9.5 WILL DROUGHTS OCCUR MORE OFTEN?____________________________________________ 9-8
9.6 WILL THE POTENTIAL TO GENERATE HYDROELECTRICITY BE AFFECTED BY CLIMATE CHANGE?9-9
9.7 WILL FLOODS BECOME MORE FREQUENT?_________________________________________ 9-11
9.8 UNCERTAINTIES AND FUTURE WORK _____________________________________________ 9-12
9.9 FINAL CONCLUSIONS AND RECOMMENDATIONS _____________________________________ 9-13
9.10 REFERENCES _______________________________________________________________ 9-17