A regional model study of the importance of local versus remote controls of the 1988 drought and the 1993 flood over the central United States

Regional model experiments for the drought period of May-June-July (MJJ) 1988 and the flood period of MJJ 1993 over the Central Plains of the United States are conducted to study the contribution of local versus nonlocal processes to the maintenance and/or enhancement of the conditions. It is found that the effect of local recycling of evaporated water is not important for the overall development of these two extreme climatic regimes as compared to the effect of large-scale moisture fluxes and synoptic cyclonic activity. In fact, sensitivity experiments indicate that in the Upper Mississippi Basin (UMB) the main effect of decreased evaporation associated with dry soil conditions at the beginning of the simulated periods is to increase buoyancy, dynamically sustain convection, and increase precipitation, thereby providing a negative feedback mechanism for the drought-flood conditions. Overall, the model shows a reasonably good performance in simulating various characteristics of surface climatology over the region during these two extreme periods, with total simulated precipitation being close to observed in MJJ 1988 and lower than observed by about 25% in MJJ 1993. The simulated surface hydrologic budgets and different precipitation statistics over the UMB are also analyzed.