The Evolution Of Agricultural Drought Transition Periods In The Us Corn Belt

Agricultural drought in the U.S. Corn Belt region (CBR) has tremendous global socioeconomic implications. Unfortunately, the weather and climate factors that contribute to transition events toward or away from such droughts are poorly understood. This study applies composite, trajectory clusters, and a vertically integrated moisture budget to understand the phenomena that influence transition events that evolve over 20 and 60 days as modulated by interannual, intraseasonal, and synoptic-time-scale variability during May-August over the CBR. Results show that a shift in the low-frequency base state does not explain onset or decay of the 20- or 60-day drought transition cases. Instead, amplification of an intraseasonal Rossby wave train across the Pacific Ocean into North America, which occurs coincident with intraseasonal tropical convection on its equatorward side, triggers the transition. Trajectory analysis reveals similar source regions for air parcels associated with drought development and breakdown, but with a shift toward more parcels originating over the Gulf of Mexico during transitions away from drought. Finally, the vertically integrated moisture budget shows that advection and convergence of moisture on intraseasonal time scales dominates during these transitions. These results demonstrate that weather events are the primary driver of agricultural drought transitions occurring over 20 and 60 days.