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

Climate impacts on environmental systems3.5.4 Soil moistureRelevanceThe ability of soil to retain moisture is a significantaspect in the water cycle and is crucial for primaryproduction (see Section 4.1). The amount of waterheld in soil is intrinsically linked to our climateand depends largely on texture, structure and theamount of soil organic matter. Variations in anyof these variables will affect soil water retentioncharacteristics and ultimately soil functions(e.g. groundwater recharge).By absorbing many times its weight in water, soilorganic matter in mineral soils can contribute to themitigation of flooding following extreme rainfallevents while storing water in the event of morefrequent and severe droughts (Reicosky, 2005;Louwagie et al., 2009). At low soil carbon contents,an increase in carbon content leads to an increasein water retention in coarse soils and a decreasein fine‐textured soils. At high carbon contents, anincrease in carbon content results in an increasein water retention for all soil textures (Rawlset al., 2003).While water-holding capacity is an intrinsic soilproperty based on clay content, structure andorganic matter levels, water content is highlydynamic and is the balance between rainfall andevapotranspiration. Changes in temperature andprecipitation patterns and intensity will affectevapotranspiration, soil moisture and infiltrationrates. Conversely, there is also observationalevidence that soil moisture deficit exacerbateshot extremes in south-eastern Europe (Hirschiet al., 2011).Past trendsThere is no clear indication on past trends for waterretention across the EU due to a lack of systematicand harmonised data. Several models have beenused to assess soil moisture, but these are oftenreliant on secondary input data (i.e. observedprecipitation and temperature). Direct observationsof spatially explicit distribution of soil moistureacross Europe are just evolving. Satellite-bornesensors, such as the European Space Agency's (ESA)Soil Moisture and Ocean Salinity (SMOS) missionor EUMETSAT's ASCAT Scatterometer, are able tomake global observations of surface soil moisture(Map 3.23). Such data, along with numericalmodelling techniques, have the potential to be usedin deriving composite maps of soil moisture levelsdown to a depth of 1–2 m, the so-called root zone.Thus, this information could help in assessing theimpacts of climatic variations, including droughts,on for example ecosystem production.ProjectionsProjections indicate greater droughts in someareas, which might lead to substantial reductions insummertime soil moisture, and marked increase inrainfall in others (Calanca et al., 2006). In particularin the Mediterranean area of southern Europe, soilwater content is expected to decline, and saturationconditions are expected to be increasingly rareand restricted to periods in winter and spring(García‐Ruiz et al., 2011). Harmonised time seriesdata on relevant soil properties should be developedas should models to assess key parameters suchas subsoil available water capacity and topsoilmoisture levels. Satellite information should beintegrated with representative observed data, alsofor projections.Key messages: 3.5.4 Soil moisture• Soil water retention is a major soil hydrological property that governs soil functioning in ecosystems andgreatly affects soil management.• There is no clear indication on past trends for water retention across the EU due to a lack of systematicand harmonised data.• Water retention capacity and soil moisture content will be affected by rising temperatures and by adecline in soil organic matter due to both changes in climate and land management.• Projections (for 2071–2100) show a general reduction in summer soil moisture over most of Europe,significant reductions in the Mediterranean region, and increases in the north-eastern part of Europe.• Maintaining water retention capacity and porosity are important to reduce the impacts of intense rainfalland droughts, which are projected to become more frequent and severe.154 Climate change, impacts and vulnerability in Europe 2012