Assessing the impact of present and future droughts on agriculture through crop vulnerability curves: the case study of the Po River basin (Northern Italy)

Drought is a significant threat for those sectors highly dependent on water resources such as agriculture. About 83% of all drought-related losses between 2005 and 2015 were suffered by the agricultural sector, according to FAO. The estimation of drought impacts on crops is fundamental to foresee the effects that future droughts will have on the sector. A quantitative evaluation of crop yield reduction due to water scarcity can be obtained through vulnerability curves. This study develops crop specific drought vulnerability curves tailored on the Po River basin (Northern Italy). The basin is the largest Italian watershed and the main agricultural area of the country accounting for 35% of the national agricultural production. Over the past years it has experienced several droughts, with the 2005-2007 having catastrophic impacts on agriculture. Results from the PRUDENCE regional experiments showed that in a climate change context the frequency and severity of droughts are expected to increase in the next century in Northern Italy, because of a decrease in precipitation during spring and summer, which are the critical crop growing seasons. To assess the impact of droughts on crops, vulnerability curves, linking water availability with yield reduction, were developed for four crop growing stages (establishment, vegetative, flowering and yield formation). The Agricultural Production System sIMulator crop model was initialized with meteorological data from the E-OBS dataset and soil data from the ISRIC dataset. At first the yield in the absence of water stress was computed (potential yield). Then a drought event was simulated during each growth stage and actual yield was computed. Yield reduction was determined as the difference between potential and actual yield. The obtained yield reduction was correlated with water availability (expressed as the ratio between crop water demand and soil water supply). Two crops were considered: maize, traditionally irrigated, and winter wheat (rainfed). Results showed that for both crops flowering is the most sensitive stage to water stress, followed by yield formation. Winter wheat is more resistant to drought with respect to maize. The developed vulnerability curves will help in evaluating the impacts that more severe droughts will have on agriculture in Northern Italy.