4 IMPACTS OF GLOBAL CHANGE AND ADAPTATION STRATEGIES IN
4.1 W ATER B ALANCE , S UPPLY AND D ISTRIBUTION
4.1.4 Impacts of Climate Change – Trends and Projections
and the Elbe 2002, are often caused by specific general weather situation (e.g. the so-called “Vb weather condition”). Again, a number of studies substantiate at least the increased frequency of such weather conditions (Fricke & Kaminski, 2202).
Besides climatic conditions, a number of other factors are important for flood risk, such as decreased regional water retention capacity due to river regulation, the construction of barrages, the loss of floodplains and wetlands, and the increased sealing of surface areas. For example, the river Rhine has already lost four-fifth of its natural floodplains.
Similarly, at the river Elbe only 15% of the natural floodplains remain (IKSE, 1996;
BMU, 2002). Moreover, agriculture causes more frequent floods by the usage of heavy machinery on arable fields and the consequent condensation of soils, which hampers the infiltration capacity. At present, the influence of these anthropogenic factors is more pronounced than climate change.
Other Factors
Besides water extraction for industry, households and agriculture, the draining of strip mines for brown coal is an important factor for the water balance. This is done in the Rhineland, the Niederlausitz, and in the region between Helmstedt and Leipzig/Halle.
The draining of mines causes a gradual drying up of wetlands, sometimes the running dry of creeks and rivers, and a decrease in the water available for public water supply.
Moreover, the water demand for the flooding of pits remaining after strip mining can threaten regional water supply (e.g. at the Spree).
Society depends not only on sufficient water quantities but also on sufficient water quality. In Germany, agriculture hampers the water quality of groundwater and receiving streams through the use of fertilisers and pesticides on arable land. These are leached to the groundwater or are transported to the surface waters through erosion, leading to eutrophication of surface waters and oceans. Charging groundwater with nutrients, such as e.g. nitrate, causes a profound loss in the usability of the aquifer as drinking water resource and can negatively impact groundwater biology.
Moreover, water resources are burdened with heavy metals, organic chemicals, and pesticides.
4.1.4 Impacts of Climate Change – Trends and Projections
-8.4- 10.3 % (∆18.7%)
-3.3- 10.3 %
(∆13.6%) 4 Models (Scenario A2) Change by 2080 -8.4--3.3%
(∆5.1%) 4 Scenarios (HadCM3)
HadCM3–B1 HadCM3–B2 HadCM3–A1
HadCM3–A2
CGCM2–A2 CSIRO2–A2
PCM–A2
Change in Mean Annual Runoff [%]
-50 -25 0 25 50
1990 2020 2050 2080
∆Q [%]
-8.4- 10.3 % (∆18.7%)
-3.3- 10.3 %
(∆13.6%) 4 Models (Scenario A2) Change by 2080 -8.4--3.3%
(∆5.1%) 4 Scenarios (HadCM3)
HadCM3–B1 HadCM3–B2 HadCM3–A1
HadCM3–A2
CGCM2–A2 CSIRO2–A2
PCM–A2 HadCM3–B1
HadCM3–B2 HadCM3–B1 HadCM3–B1 HadCM3–B2 HadCM3–B2 HadCM3–A1
HadCM3–A2 HadCM3–A1 HadCM3–A1 HadCM3–A2 HadCM3–A2
CGCM2–A2 CSIRO2–A2 CGCM2–A2 CGCM2–A2 CSIRO2–A2 CSIRO2–A2
PCM–A2 PCM–A2
Change in Mean Annual Runoff [%]
-50 -25 0 25 50
1990 2020 2050 2080
∆Q [%]
Fig. 4.1-3: Relative change in mean annual runoff up to 2080 compared to 1990 for seven ATEAM scenarios.
The interpretation of drought runoff (Q90) is more revealing than the analysis of annual runoff. Q90 (drought runoff) is the annual runoff that is exceeded in nine years out of ten. That is, the runoff in one out of ten years lies under the Q90 value.
Therefore this value is an indicator of the runoff to be expected in arid years. On the whole, the development of drought runoff over time within this century in Germany shows a similar picture as annual runoff (Fig. 4.1-4).
-9.6– 12.3 % (∆21.9%)
-4.4– 12.3 %
(∆16.7%) 4 Models (Scenario A2) Change by 2080 -9.6–-3.4%
(∆6.2%) 4 Scenarios (HadCM3)
HadCM3–B1 HadCM3–B2 HadCM3–A1
HadCM3–A2
CGCM2–A2 CSIRO2–A2
PCM–A2
Change in Drought Runoff Q90 [%]
-50 -25 0 25 50
1990 2020 2050 2080
∆Q [%]
-9.6– 12.3 % (∆21.9%)
-4.4– 12.3 %
(∆16.7%) 4 Models (Scenario A2) Change by 2080 -9.6–-3.4%
(∆6.2%) 4 Scenarios (HadCM3)
HadCM3–B1 HadCM3–B2 HadCM3–A1
HadCM3–A2
CGCM2–A2 CSIRO2–A2
PCM–A2 HadCM3–B1
HadCM3–B2 HadCM3–B1 HadCM3–B1 HadCM3–B2 HadCM3–B2 HadCM3–A1
HadCM3–A2 HadCM3–A1 HadCM3–A1 HadCM3–A2 HadCM3–A2
CGCM2–A2 CSIRO2–A2 CGCM2–A2 CGCM2–A2 CSIRO2–A2 CSIRO2–A2
PCM–A2 PCM–A2
Change in Drought Runoff Q90 [%]
-50 -25 0 25 50
1990 2020 2050 2080
∆Q [%]
Fig. 4.1-4: Relative change in drought runoff Q90 up to 2080 compared to 1990 for seven ATEAM scenarios. Q90 (drought runoff) is the annual runoff that is exceeded in nine years out of ten.
The range of change in drought runoff by 2080 is –10% to +12%. There are strong regional differences, with local decreases of over 50% in some parts of Northern and Eastern Germany (Fig. 4.1-10 in the Annex). However, again different climate models produce different regional patterns.
Results for summer runoff (runoff during the months June, July and August; Fig. 4.1-5) show an even more differentiated pattern. Water availability is distinctly reduced in summer according to five of the seven climate scenarios, due to the shift of precipitation from summer to winter that is projected by many climate models, and
owing to the temperature increase, which increases evapotranspiration, and particularly transpiration (through plants) (change by 2080 in comparison to 1990 of – 43% to +5%). This reduction in water availability is projected across all parts of Germany (Fig. 4.1-11 in the Annex).
The degree to which a region is hit by changes in runoff depends strongly on the size of the change and on the initial situation. Especially regions that presently have an unfavourable water balance and low runoff, such as e.g. the central regions of Eastern Germany (Fig. 4.1-1), can be strongly impacted by climate change. In these regions, the shift of precipitation from summer to winter leads to further decreases in summer runoff, when the situation has already been difficult in arid years, and causes further water shortages. Even if the results vary between climate models, there is considerable evidence that climate change will increase the risk of arid periods and droughts.
∆Q [%]
-50 -25 0 25 50
1990 2020 2050 2080
-43.0- 5.5 % (∆48.5%)
-27.6- 5.5 %
(∆12.1%) 4 Models (Scenario A2) Change by 2080 -43.0--24.2%
(∆18.8%) 4 Scenarios (HadCM3)
HadCM3–B1 HadCM3–B2 HadCM3–A1
HadCM3–A2
CGCM2–A2 CSIRO2–A2
PCM–A2
Change in Summer Runoff [%]
∆Q [%]
-50 -25 0 25 50
1990 2020 2050 2080
-43.0- 5.5 % (∆48.5%)
-27.6- 5.5 %
(∆12.1%) 4 Models (Scenario A2) Change by 2080 -43.0--24.2%
(∆18.8%) 4 Scenarios (HadCM3)
HadCM3–B1 HadCM3–B2 HadCM3–A1
HadCM3–A2
CGCM2–A2 CSIRO2–A2
PCM–A2 HadCM3–B1
HadCM3–B2 HadCM3–B1 HadCM3–B1 HadCM3–B2 HadCM3–B2 HadCM3–A1
HadCM3–A2 HadCM3–A1 HadCM3–A1 HadCM3–A2 HadCM3–A2
CGCM2–A2 CSIRO2–A2 CGCM2–A2 CGCM2–A2 CSIRO2–A2 CSIRO2–A2
PCM–A2 PCM–A2
Change in Summer Runoff [%]
Fig. 4.1-5: Relative change in summer runoff (June – August) up to 2080 compared to 1990 for seven ATEAM scenarios.
Low water and droughts have severe consequences for almost all sectors considered in this study. Agriculture, forestry, energy and drinking water providers, as well as public bodies will have to prepare for recurring arid periods in Germany. Moreover, wetlands and aquatic ecosystems are threatened. In general, there is a clear need for a well-balanced adaptation strategy, which includes storage, limitations in water demand, and alternative sources of water.
Risk of Flood Events
A number of scientists expect a generally increased risk of extreme rainfall events and floods as a consequence of climate change (Palmer & Räisänen, 2002; Milly et al., 2002). Climate change is also expected to impact flood development in Germany, due to changes in precipitation characteristics (Bronstert, 1996). This concerns not only the absolute amount of precipitation, but also intensity, duration and frequency of rainfall events. Regional trends in precipitation development are ambiguous (Eisenreich, 2005), however, there is considerable evidence for a decrease in summer precipitation and an increase in winter and spring precipitation, leading to an increase in the probability of winter floods.
Decreased snowmelt owing to temperature-induced decreases in snow accumulation could, however, reduce the flood peaks (Eisenreich, 2005). Furthermore, decreased frequency of the freezing up of rivers due to temperature increase reduces the probability of floods triggered by ice accumulation, such as have been primarily observed at the Elbe river in the past (Bronstert, 1996).
Integrated Results for Specific Watersheds
Runoff at the river Rhine is expected to shift to early spring, owing to the shift of precipitation from summer to winter (Middlekoop & Kwadijk, 2001). The ATEAM scenarios also project this shift (Fig. 4.1-6). The HadCM3-A2 scenario shows a shift of monthly peak flows of the Rhine (at the water gauge Kaub) from May/June (1990) to March (scenario for 2050).
Detailed case studies for three study regions in the Rhine watershed from the project LAHoR (Bardossy et al., 2003) estimate a decrease in precipitation in November and December, accompanied by an increase in precipitation during the months of March and April by 2080. Based on these finding, the probability of the typical “Christmas floods” at the Rhine will potentially decrease. On the other hand, the probability of flood events in spring increases. This is caused by the increase in precipitation in early spring, as well as by the simultaneous snowmelt in the Alps and higher low mountain ranges.
These results are in accordance with findings of the research group KLIWA, which also project a potential increase in flood risk during winter and early spring for the Rhine (Krahe et al., 2004).
Mean Monthly Runoff along the Rhine at the Water Gauge Kaub
km3month-1
2050 (HadCM3-A2) 1990
Mean Monthly Runoff along the Rhine at the Water Gauge Kaub
km3month-1
2050 (HadCM3-A2) 1990
Fig. 4.1-6: Mean monthly runoff along the river Rhine at Kaub 1990 and 2050, climate scenario calculated by climate model HadCM3 with A2 emissions (ATEAM result).
The research group KLIWA also offers results for the watershed of the upper Main (Barth et al., 2004) and the Neckar (Gerlinger, 2004). These results corroborate the trend of shifting runoff to the months February, March, April, as well as a potential increase in flood risk during this time.
Some studies project decreasing water availability in the Elbe watershed. In this region a decrease in runoff by approximately 40% (Wechsung, 2004) and of groundwater recharge of next to 50% (Hattermann et al., 2004) is expected, on the assumption of decreasing annual precipitation up to 2050.
Further Impacts of Climate Change
Changes in river runoff impact water levels and water quality of lakes and canals directly (Eisenreich, 2005). Particularly in shallow and warm water bodies, the growth of zoo- and phytoplankton and therefore the risk of eutrophication can increase, due to declining water levels, increasing warming and increasing suspension of sediment. This development impacts not only drinking water provision, but also sectors such as tourism. For example, decreasing summer precipitation and declining inflow from the headwater threaten the tourism region Spreewald (forested region around the river Spree near Berlin) (Dietrich, 2004).
Potential decreases in water supply especially in the summer month also cause problems in the recultivation and flooding of the remaining pits after strip mining in Eastern Germany (Kaltofen et al., 2004).
Currently no detailed studies are available on the impact of climate change on drinking water supply in Germany. In general no shortages in drinking water are expected, despite decreasing amounts of groundwater storage in North and West Germany, as well as parts of East Germany (BMU, 2001).