The Role of Horizontal Resolution in Modeling Irrigation Effects With a Coupled Regional Climate Model System Up To Convection-Permitting Scale

Abstract

Increasing the resolution of regional climate models (RCMs) up to convection-permitting scales enables explicitly resolved convection and finer resolved surface features. In this work, we use the benefits of the high resolution climate model and apply it to model irrigation effects and feedbacks on the local and regional climate, focusing on the interaction of irrigation with soil, surface, atmosphere, and vegetation processes. We employ the RCM REMO2020 interactively coupled to its vegetation module iMOVE and incorporate our newly developed irrigation parameterization. We conduct two simulation sets with and without the irrigation parameterization. In the first set, we employ the hydrostatic model version at 0.11° horizontal resolution for Southwestern Europe. For the second set, we repeat the experiment employing the non-hydrostatic model version at convection-permitting resolution of 0.0275° for Northern Italy. Our results indicate that improved vegetation conditions due irrigation, such as an increased canopy conductance, lead to effects in the atmosphere. For the atmosphere, we find more distinct and localized irrigation effects for the simulations at convection-permitting resolution with enhanced near-surface cooling of up to −2 K compared to the simulations at 0.11°. In the boundary layer, irrigation effects are highly influenced by turbulence, transporting the irrigation effect to higher levels. The largest differences in representing irrigation effects on the two resolutions were found in precipitation. While at 0.11° horizontal resolution, precipitation increases due to favorable convection conditions, explicitly resolving convection leads to rather mixed effects with a decrease of precipitation above irrigated areas, where the convection inhibition increased.