Influence of Irrigation on Mid-Summer Convective Rainfall in the Great Plains

The effects of irrigation on boundary layer dynamics, mediated by the partitioning of flux between sensible and latent heat, suggest the possibility of influencing precipitation behavior downwind of irrigated sites. However, previous modeling studies have had difficulty in unambiguously attributing variations in precipitation to the effects of irrigation. This ambiguity likely arises from the temporal and spatial variability of irrigation in the Great Plains, which is underresolved by traditional regional climate models integrated over relatively short time periods from hours to days. This study seeks to identify the effects of irrigation on precipitation over the Great Plains by employing a convection-resolving regional climate model framework. The Weather Research and Forecasting (WRF-ARW) model is integrated over a 4-km horizontal grid with 48 vertical layers, for the relatively climatically average month of July 2001. WRF simulations are compared for irrigated and non-irrigated soil moisture conditions. The control case represents non-irrigation conditions, where soil moisture is only replenished by rainfall. To represent irrigation, soil moisture is nudged toward field capacity for sites identified by the USGS land use classification as being either irrigated crop and pasture or irrigated crop/grassland mosaic. By doing so, we will clearly identify the impacts of irrigation on largely local and mesoscale driven summer months.