Climate change, impacts and vulnerability in Europe ... - MemoFin.fr

Climate impacts on environmental systems3.3 Freshwater quantity and quality3.3.1 OverviewWater is essential to life and is an indispensableresource for ecosystems and for nearly all humanactivities. It is intricately linked with climate suchthat any alteration in the climate system will inducechanges in the hydrological cycle. Consequently,the spatial and temporal distribution of freshwaterresources and those socio‐economic activitiesdependent upon water are affected by climatevariability and climate change.There is growing evidence that climatic changesin recent decades have already affected the globalhydrological cycle, such as by changes in seasonalriver flow and increasing severity and frequency ofboth floods and droughts in some regions. However,the detection of significant long-term trends inhydrological variables is generally difficult dueto substantial interannual and decadal variability.Furthermore, the attribution of observed changesis complicated because of modifications to naturalwater flow arising from water abstractions and landusechange.Indicator selectionThis section presents information on the followingindicators:• River flow: This indicator monitors changes inannual and seasonal river flow, which is centralfor water availability to households, industryand agriculture.• River floods: This indicator monitors changes inriver floods events, which are among the mostcostly weather disasters in Europe.• River flow droughts: This indicator monitorschanges in low river flow, which can havesignificant negative impacts on households,industry, navigation, agriculture and ecosystems.• Water temperature of rivers and lakes: Watertemperature is one of the central parametersthat determine the overall health of aquaticecosystems because aquatic organisms havea specific range of temperatures that they cantolerate.• Lake and river ice: This indicator is relevant forfreshwater ecosystems and for transport.The concluding subsection presents selectedinformation on the impacts of past and projectedchanges in these indicators for freshwater ecosystemsand water quality. This information is not presentedin the indicator format because the impacts foreseenfor different aquatic species and ecosystems are sodiverse that the message cannot be conveyed in oneindicator.Further information on the health and economicrisks of floods and droughts is presented inSection 4.4 and in Chapter 5.Key messages: 3.3 Freshwater quantity and quality• Climate change has already affected river flow but other factors also have a strong influence.• In general, river flows have increased in winter and decreased in summer, but with substantial regionaland seasonal variation.• The impact of river flow droughts is currently largest in southern and south-eastern Europe. Theseimpacts are projected to further increase with prolonged and more extreme droughts.• Climate change has increased water temperatures of rivers and lakes, and has decreased ice cover.• Changes in stream flow and water temperature have important impacts on water quality and onfreshwater ecosystems.112 Climate change, impacts and vulnerability in Europe 2012