Retrospective droughts in the crop growing season: Implications to corn and soybean yield in the Midwestern United States

The Midwestern United States has experienced many severe droughts in the period of 1916–2007. We reconstructed and examined the occurrence of meteorological, hydrological, and agricultural droughts using a long-term (i.e. 1916–2007) dataset of gridded observed precipitation and simulated soil moisture and runoff from the Variable Infiltration Capacity (VIC) model for Illinois and Indiana. Reconstructed droughts were analyzed for periods of the year relevant for the development of corn and soybean crops including: (i) the beginning of the crop growing period, (ii) the grain filling and reproductive growth period, and (iii) the entire crop crowing season. Our results indicated that the most severe and widespread (affecting more than 90% of the two states) droughts occurred in the 1930s affecting the entire crop growing season for 1930, 1931, 1934 and 1936. The severity and extent of droughts have decreased in the second part of the last century with only one year, 1988, approaching the severity and extent of the droughts of the 1930s. Analysis of long-term trends in drought indices indicated that the two state area has become wetter in the crop-growing season over the last 92 years, mainly due to observed increases in precipitation. Crop yields during the period of 1980–2007 were strongly correlated with the occurrence of meteorological drought and maximum daily temperature during the grain filling and reproductive growth period. Therefore, decreasing trends of maximum daily temperature with increased wetness create favorable conditions for better crop yields in the study domain.