Climate Change and Switzerland 2050 - OcCC - SCNAT

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Climate Change and Switzerland 2050 | Water management 63 4. Water supply and demand Groundwater recharge Groundwater recharge will tend to increase in winter and decrease in summer and autumn as a result of climate change. Overall, groundwater levels will decrease slightly. In Switzerland, 83% of the drinking and industrial water demand is covered by groundwater; 44% of which come from springs in karst and fissure aquifers and 39% from filter wells in unconsolidated rock (see fig. 4). Unconsolidated rock aquifers have a slow groundwater flow and are generally plentiful. In karst areas, the groundwater drains off quickly, which is why springs there show a large discharge after rain. Springs in fissured rock areas show a steadier discharge but are generally less plentiful. The different aquifer types therefore react to climate change to a different extent and with a different delay. As a result of the predicted climate change, groundwater recharge will tend to increase in winter as a result of increased precipitation in the form of rain. In summer and autumn, groundwater recharge will decrease in the midlands and in the foothills of the Alps due to higher temperatures, more frequent drought periods and the concentration of intense precipitation. Infiltration from alpine surface waters will decrease slightly. As a result of these changes in groundwater recharge, spring deliveries in near-surface wells with small catchment areas and in karst aquifers will fluctuate more strongly from season to season, and may partly run dry in summer and autumn. In groundwater reservoirs in valley gravels with a midland flow regime, groundwater levels are expected to fall in summer and autumn. Groundwater reservoirs in valley gravels with an alpine flow regime, which exhibit their seasonal peak in summer, will experience only slightly falling water levels. However, even here lower groundwater levels must be expected during the more frequently occurring heat wave summers and absence of glacier melt in late summer and autumn. In aquifers at lower elevations, a slight decrease in groundwater levels is also expected. Unconsolidated rock groundwater aquifers Karst groundwater aquifers Fissured rock groundwater aquifers Figure 4: Distribution of the different aquifers in Switzerland. 16
64 Climate Change and Switzerland 2050 | Water management Demand for drinking and industrial water As a result of climate change, competition between different water uses and users will become more frequent. The requirements for drinking water supply will be affected regionally and temporally. In agriculture, the demand for irrigation water will increase. Climate change will affect the requirements for drinking water supply. The effects are regionally and temporally very different. Measures against drinking water shortages and to increase supply security include the use of surface water (lakes), the expansion of the integrated networks of the drinking water supply and the development of new groundwater resources. Water resources will decrease in the soil due to decreasing precipitation in summer. Higher temperatures lead to an increase in evaporation and in the demand of plants for water (transpiration). As a result, longer-lasting and more frequent drought periods will lead to soil dehydration. Consequently, 5. Water use In Switzerland, water is extensively used for energy production. As a result of climate change, electricity production by storage and run-of-river power stations will decrease. In the future, Rhine shipping will increasingly be affected by extended periods with unusually low water levels. Energy In Switzerland, water power covers about 60% of the demand for electricity or 1 / 8 of the entire energy demand. Climate change will lead to a seasonal balancing of discharge regimes, particularly in the Alpine region. Water flow will increase in winter and spring, and decrease in summer and autumn. As a result, power plant operators gain more flexibility. In the future, the use of water-storage space will be adjusted not only to the balancing of seasonal fluctuations but also to the fluctuations of the electricity market. Overall, a loss in hydroelectric energy production by storage power stations must be anticipated, since less water will be available; annual rainfall will decrease and evaporation increase. Low water levels in late summer and autumn will limit the electricity production of run-ofriver power stations in the midlands. On the other hand, these power stations can profit from the the water absorption capacity of the soil declines due to crustification and water retention capacity declines due to desiccation cracks; the ability to produce humus decreases. Reduced water supply and increased agricultural demand for irrigation water will lead to a competitive situation between different uses und users, such as with downstream users. In summer, water – limited temporally and spatially – will increasingly become a scarce commodity. Thus, the necessity of suitable management will increase, which will affect the priorities, rights and prices for use. Compensation and irrigation measures will require rules as well as new infrastructure. increasing discharge in winter and spring, since the capacity of turbines at that time of year are hardly working to full capacity today. 17 Altogether, a minor decrease in electricity production by runof-river power stations is to be expected. 18 Floods and slope instabilities will increase with climate change, and in particular large mass movements can endanger auxiliary facilities of power plants, such as water catchments on steep slopes. Sediment, bed load and debris flow transport could increase, intensifying and accelerating the silting up of storage lakes. 19,20 The production in nuclear and other thermal power plants will also be affected by climate change. Due to increasing water temperatures and decreasing discharge, they will not be able to obtain as much cooling capacity from the water as today, in particular during heat waves like in the summer of 2003. Due to climate policy, water power as a renewable CO 2-free energy will gain economic advantages.
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Climate Change and Switzerland 2050 - OcCC - SCNAT

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