Climate-Risk Assessment for Crop Production: A Case-Study for Winter Wheat in the U.S. Southern Great Plains.

Water-deficit (WD) and extreme temperature stresses during the winter wheat growing season can limit grain yield. We used 30-year daily weather data to estimate probability (P) of WD, and freeze and heat stresses in wheat varieties with different maturities in 68 locations across the U.S. southern Great Plains. Heading date was calculated using 730, 920, and 1112 growing degree days (GDD) from January 1^st for early, medium and late varieties. We then estimated the probability of WD at sowing in the fall and heading in the spring by subtracting 15-d sum of precipitation by 15-d sum of evapotranspiration considering WD stress when this difference surpassed 60% of each soil’s available water capacity. We evaluated number of days with P of T_min<0°C during heading-anthesis interval, T_max>27°C prior to anthesis, and T_max>33°C prior to soft dough. Number of days from 1 January to heading averaged 110, 123, and 133 days for early, medium, and late maturing varieties. Number of days prior to sowing in the fall with WD P>0.2 increased from zero in eastern locations to 53 days in western locations. Similar gradient was found for the heading period, where WD P>0.2 initiated 52 days prior to heading in western locations and up to 66 days after heading in eastern locations. While early varieties had lower risk of WD after heading versus late varieties (0 vs. 20-d); they had greater risks of spring freeze (21 vs 0–d around heading T_min<0). Heat stress during the reproductive period was more likely to occur in the west, with 43 versus 20-d prior to anthesis with P of T_max>27°C, and 13.5 vs. 0-d days prior to soft dough with P of T_max>33°C for late and early varieties, respectively. The climate-risk assessment methodology developed is promising and can be expanded to different regions and cropping systems.