SWS and EWS events (table S1) were first defined to quantify the short- and long-term impacts of water shortage on crops. A grid cell was considered to be affected by water scarcity only if both the short-term water scarcity indicators (i.e., 1- and 3-month SPEI) and the long-term water scarcity indicators (i.e., 12-month SPEI) reached predefined thresholds (table S1). The thresholds were adopted on the basis of Blauhut et al. (71), where the probability of drought impact occurrence was estimated on the basis of the impacts of drought on individual sectors. Because wheat is only grown during part of the year, we used two specific water scarcity sensitivity periods (SPs):

1) The wheat growing season, i.e., from the usual regionally specific month of sowing to the month of harvest. In regions where both spring and winter wheat were grown, the sowing date of the prevailing wheat season was analyzed.

2) Four months before the usual wheat harvest, i.e., the period that included both the peak vegetative stage (before the heading) and grain filling. Both stages are very sensitive to soil moisture deficits. These four months constitute the time of the most intense growth, including the formation of all yield components.

When the usual harvest date was on or later than the 20th day of the month, the drought index for the month of harvest and the three preceding months was used. When wheat was harvested before the 20th day of the harvest month, the drought index for the 4 months before the month of harvest was used. This offset was used because the harvest date of wheat, in practice, follows the physiological maturity of wheat by several days or even weeks, and the sensitivity of wheat to drought decreases rapidly at the end of the grain filling stage and postmaturity. Drier conditions during harvest are generally beneficial for wheat quality and could increase the efficiency of the harvest. In all calculations, calendar months were used.

The overall differences in drought indexes resulting from using the different SPs (fig. S7) were small and, at most, five percentage points during the control run. Therefore, a 4-month SP was primarily used in the study, as it allowed us to consider water scarcity over the same length of time across all wheat-growing regions. In most cases, the area affected by water scarcity was larger when the SP was defined from sowing to harvest, rather than as the 4 months before harvest.

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