Soil Moisture Influence on Warm-Season Convective Precipitation for the U.S. Corn Belt

Abstract

Abstract Recent climatic studies for the dominantly rain-fed agricultural U.S. Corn Belt (CB) suggest an influence of land-use/land-cover (LULC) spatial differences on convective development, set within the larger-scale (synoptic) atmospheric conditions of pressure, winds, and vertical motion. However, the potential role of soil moisture (SM) in the LULC association with atmospheric humidity, horizontal wind, and convective precipitation (CVP) has received more limited attention, mostly as modeling studies or empirical analyses for regions nonanalogous to the CB. Accordingly, we determine the categorical associations between SM and the near-surface atmospheric humidity q, with 850-hPa horizontal wind V 850 at four representative CB locations for the nine warm seasons of 2011–19. Recurring configurations of joint SM–q–V 850 conducive to CVP are then identified and stratified into three phenologically distinct subseasons (early, middle, and late). We show that the stations show some statistical similarity in their SM–CVP relationships. Corn Belt CVP occurs preferentially with high humidity and southerly winds, sometimes composing a low-level jet (LLJ), particularly on early-season days having low SM and late-season days having high SM. Additionally, midseason CVP days having weaker V 850 (i.e., non-LLJ) tend to be associated with medium SM values and high humidity. Conversely, late-season CVP days are frequently characterized by high values of both SM and humidity. These empirical results are likely explained by the inferred sensible and latent heat fluxes varying according to SM content and LULC type. They provide a basis for future mesoscale modeling studies of Corn Belt SM and CVP interactions to test the hypothesized physical processes. Significance Statement The effects of soil moisture on precipitation are not well understood, as previous research has found contrasting results depending on study region and period of focus. We determine these associations for the Corn Belt, a humid lowland region that has received less attention than the drier neighboring Great Plains. Our study finds strong soil moisture–precipitation relationships in the presence of high humidity, which may be explained by mechanisms associated with the subseasonal cycle of vegetation activity. Additionally, our results suggest a generally weaker influence of soil moisture on precipitation for the Corn Belt than for the Great Plains, highlighting the importance of understanding how these relationships vary spatially. Future work should test the inferred surface–atmosphere mechanisms introduced here using mesoscale modeling.