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

Climate impacts on socio-economic systems and health4.1.2 Growing season for agricultural cropsRelevanceThe thermal growing season is a basic agrologicalindicator for where and when crops can potentiallybe grown, assuming sufficient water, radiationand suitable soils. The duration of the growingseason is for a large part of Europe defined by theduration of the period with temperatures abovea certain threshold. The duration of the frost-freeseason is considered the period favourable forgrowth of many plant species (e.g. for flowering).However, active growth of plants requires highertemperatures, and for most of the temperate cropsgrown in Europe a threshold temperature of 5 °Ccan be used (Trnka, Olesen, et al., 2011).Past trendsIncreasing air temperatures are significantlyaffecting the duration of the growing season overlarge areas of Europe (Scheifinger et al., 2003). Manystudies report a lengthening of the period betweenthe occurrence of the last spring frost and the firstautumn frost. This has occurred in recent decadesin several areas in Europe and more generally in theNorthern Hemisphere (Trnka, Brázdil, et al., 2011).Studies of changes in the growing season basedon remote sensing show a diverse spatial patternin Europe (Schwartz et al., 2006). Across all ofEurope, the delay in end of the season of the period1992–2008 by 8.2 days was more significant thanthe advanced start of the season by 3.2 days (Jeonget al., 2011).An analysis of the frost-free period in Europebetween 1975 and 2010 shows a general and clearincreasing trend. The trend is not uniformly spreadover Europe. The highest rates of change (largerthan 0.8 days per year) were recorded along theAtlantic shores, in the British Isles, Denmark, centralparts of Europe, central Italy, central and southernSpain, and in Turkey (Map 4.1). There are also areasin Europe with an apparent trend for reductions inthe frost-free period; however, these trends are notsignificant.ProjectionsA warming of the climate is expected mainly toresult in an earlier start of the growing season inspring and a longer duration in autumn (Jeonget al., 2011). A longer growing season allows theproliferation of species that have optimal conditionsfor growth and development and can thus increasetheir productivity or number of generations(e.g. crop yield, insect population). This will in manycases also allow for introduction of new speciespreviously unfavourable due to low temperaturesor short growing seasons. This is relevant forintroduction of new crops, but will also affect thespreading of weeds, insect pests and diseases (Rooset al., 2010).A further lengthening of the growing season aswell as a northward shift of species is projectedas a result of the projected further increase intemperature across Europe (Olesen et al., 2011). Thedate of last frost in spring is projected to advanceby about 5–10 days by 2030 and by 10–15 days byKey messages: 4.1.2 Growing season for agricultural crops• The thermal growing season of a number of agricultural crops in Europe has lengthened by 11.4 dayson average from 1992 to 2008. The delay in the end of the growing season was more pronounced thanthe advance of its start.• The growing season is projected to increase further throughout most of Europe due to earlier onset ofgrowth in spring and later senescence in autumn.• The projected lengthening of the thermal growing season would allow a northward expansion ofwarm‐season crops to areas that were not previously suitable.160 Climate change, impacts and vulnerability in Europe 2012