Influence of Irrigation on Diurnal Mesoscale Circulations: Results From GRAINEX

In order to understand the impact of irrigation on weather and climate, the 2018 Great Plains Irrigation Experiment collected comprehensive observations straddling irrigated and non-irrigated regions in southeast Nebraska. Using these observations, we examine how irrigation affects diurnal terrain-generated slope circulations, specifically the slope wind. We find that irrigation applied to upslope regions of gently sloping terrain reduces terrain-induced baroclinicity and the associated pressure gradient force by up to two-thirds. This leads to the reduction in the afternoon and evening upslope wind and is supported through comparisons to the High-Resolution Rapid Refresh operational model, which does not explicitly account for irrigation. Additionally, the presence of irrigation decreases daytime sensible heat flux (Bowen ratio reduced 40% compared to non-irrigated regions), weakening turbulent transport of momentum. Modifications to the terrain-forced circulation by irrigation has the potential to affect moisture transport and thus cloud and precipitation formation over the Great Plains.