Crop evapotranspiration under extreme weather conditions If a simulated future “extreme weather” climate condition (2050+1) is considered (created by adding +1°C to daily temperature of 2050 climate scenario), the following observations on crop cycle length are reported (fig.38): ‐ with current variety, a further important reduction of the total growing cycle is predicted for quite all planting dates with respect to 2000 and 2050 scenario, because of the faster accumulation of the required GDD sum; Planting date ‐ if a late maturing variety is considered, the total crop cycle length (2050+1 late_var) is partly recovered with respect to present (2000) scenario only in the case of late planting dates (January, February), while it is significantly shortened in all other cases with respect to 2050 late_var and 2000 scenarios. February Jaunuary 2050+1 late var 2050+1 2050 late_var 2050 2000 December November October 0 50 100 150 200 250 Cycle length (days) Fig. 38 – Length of total growing cycle of wheat in Merguellil catchment (Tunisia)as affected by planting date and variety selection under “present (2000)”, “future (2050)” and “future extreme weather (2050+1)” climate conditions. The impact of future “extreme weather” conditions (2050+1) on maximum and effective crop evapotranspiration as well as on net irrigation requirements, also considering the relative effect of selected adaptation strategies (planting dates, variety selection and deficit irrigation strategies), is summarized in the following tables and graphs. In brief, the following observations are reported: ‐ ETc_max is projected to reduce for the current variety under future “extreme weather” (2050+1) scenario as a consequence of the expected further shortening of the crop growing cycle, on average of about –6.8% with respect to present conditions (2000); on the contrary, if a late maturing variety (2050+1 late_var) is selected, ETc_max is projected to increase (+5.1% on average) (tab. 52); ‐ ETc_max is observed always to increase (in absolute terms) for late (February) planting date with respect to earlier (October) ones, because of the shifting of most of the cycle towards the hotter spring‐summer season (fig. 39 and tab.52); ‐ the relative effect of the projected variation of rainfall patterns (close to ‐40%) seems to be relevant for the crop water balance, because of the reduction of about 50 mm during the cropping season (tab. 53); ‐ ETc_eff is projected to decrease under 2050+1 scenario if the current variety is used; if ...
