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

Climate impacts on socio-economic systems and health4.1.4 Water-limited crop productivityRelevanceCrop biomass production derives from the captureand conversion of solar energy through the processof photosynthesis. However, this process maybe restricted by low (or high) temperatures orby water limitations. (Trnka, Olesen, et al., 2011)developed a simple index by which the effectiveannual radiation for plant growth was estimated bysumming daily contributions of solar radiation ondays with mean temperature above 5 °C, minimumtemperature above 0 °C and sufficient soil waterfor supporting crop transpiration. In practice theresponse depends on soil type that may have largedifferences in capacity for storing soil moisture andon possibilities for supplementary irrigation. Cropyield also depends on the timing of the crop growthand yield formation. Yields in cereal and oilseedcrops respond particularly to the duration of thegrain filling period (Kristensen et al., 2011). Theimpacts of unfavourable meteorological conditionsand extreme events vary considerably, depending onthe timing of occurrence and the development stageof the crops (Moriondo et al., 2011). Changes in theoccurrence of extreme events such as heat waves,droughts, heavy precipitation and floods will greatlyaffect crop yield leading to increased variability andeconomic consequences (Ciscar et al., 2011).Past trendsA global analysis of yields of cereal crops (wheat,maize and barley) has shown yield decreasesdue to increasing mean temperatures (Lobell andField, 2007). Similar effects have been observed forvarious countries in Europe (Kristensen et al., 2011).Increasing temperatures have also been attributed asone of the main causes for the lack of yield increaseof winter wheat in France despite improvementsin crop breeding (Brisson et al., 2010). Grain yieldsin maize have been steadily increasing in northernEurope, whereas yields in southern Europe seemto have been stagnating. There is also a tendencyfor increasing variability of grain yields in Franceand Italy, linked to occurrence of heat waves anddroughts (Olesen et al., 2011). These climaticextremes affected the crop production in large areasof southern and central Europe in 2003 and 2007.In contrast to cereals and oilseed crops, potato andsugar beet seem to have responded positively to theincreasing temperatures by increasing yields, mostlikely due to longer growing seasons (Peltonen-Sainio et al., 2010).ProjectionsThe impact of future changes in climate oncrop yield depends on the characteristics of theclimatic change within a region as well as on acombination of other environmental, economic,technological and management factors (Reidsmaet al., 2010). The index of effective solar radiationsum has been developed as a proxy for the effects ofenvironmental changes on crop productivity (Trnka,Olesen, et al., 2011)), and it integrates the daily solarradiation on those days where neither temperaturenor soil moisture is limiting for growth. This indexestimates the potential for rain-fed crop productionusing a standard soil across the entire continent,although this may be greatly modified by local soilconditions. Map 4.4 shows the projected changesin effective radiation sum for the 2040s for climateprojections from two different climate models. Bothprojections show reduced production potential inlarge parts of southern Europe and increases inthe far north, but they differ substantially for areasin-between. A broader analysis of climate changescenarios for agricultural productivity in Europehas provided a clear picture of deterioration ofagroclimatic conditions from increased droughtKey messages: 4.1.4 Water-limited crop productivity• Yields of several crops (e.g. wheat) are stagnating, whereas yields of other crops (e.g. maize innorthern Europe) are increasing; both effects are partly due to the observed climatic warming.• Extreme climatic events, including droughts and heat waves, have negatively affected crop productivityduring the first decade of the 21st century, and this is expected to further increase yield variabilityunder climate change.• Crop yields will be affected by the combined effects of changes in temperature, rainfall and atmosphericCO 2concentration. Future climate change can lead to yield decreases or increases, depending on croptype and with considerable regional differences across Europe.Climate change, impacts and vulnerability in Europe 2012165