Influence of Drought on U.S. Crop Production: Variability and Sensitivity of Response.

Increasing global populations and the accompanying rise in food demand require a reliable food supply. Recent work has explored the role of climate trends such as increasing temperature and CO₂ in affecting US agricultural production. Drought, however, is a complex phenomenon influenced by temperature, precipitation, solar radiation, and atmospheric vapor pressure, as well as their interactions. Long-term studies of drought impacts on agricultural production are rare, and in particular the impacts of different durations of drought remain unknown. We used a new gridded US-scale daily meteorological dataset to calculate the Standardized Precipitation-Evapotranspiration Index (SPEI) across 14 different time lags, and compared to county-level detrended corn and soybean yield for the period 1958-2007 to estimate the variability and sensitivity of yield response to drought. We found that drought explained a substantial (>10%) fraction of interannual yield variability, and short-term drought (1-3 month) was the best predictor for a majority of counties. In particular, July drought severity at a 1-month lag exerted the strongest control over yield, indicating that drought occurring during the critical pollination period has the largest impact on yield. Furthermore, there was large spatial variability in the drought impacts, with the greatest negative impacts in the central and southeastern US. However, we also found that more severe droughts were associated with some yield gains in Nebraska, Kansas, and cooler northern regions, which may be associated with irrigation use, soil type, depth to groundwater, and other management and climate effects.