Effects of Lateral Flow on Surface–Atmosphere Feedbacks and Convection in a Coupled Mesoscale Atmospheric and Distributed Hydrologic Modeling System for a Semiarid Environment

Evidence for surface and atmosphere coupling is corroborated in both modeling and observation-based field experiments. Recent advances in high-performance computing and development of convection-permitting regional-scale atmospheric models combined with high-resolution hydrologic models has made modeling of surface atmosphere interactions feasible for the scientific community. These models can account for the impacts of the overland flow and subsurface flow components of the hydrologic cycle. One such model is the Weather Research and Forecasting (WRF) regional atmospheric model that can be coupled to the WRF-Hydro hydrologic model.

In the present study, we examine the impacts of WRF-Hydro compared to the Noah-MP land surface model (LSM), both executed as an offline LSM with external forcing and as boundary conditions within a Regional Climate Model (RCM). Our study area is Central Arizona, a semi-arid environment, during the North American Monsoon (NAM) season. In this environment, diurnal convection is impacted by precipitation recycling from the land surface. In an RCM configuration, the uncoupled WRF (advanced research WRF; WRF-ARW) and otherwise identical WRF-Hydro model are executed for the 2017 and 2018 summertime NAM seasons. Understanding of NAM convection is critical to both the research and the operational communities, as extreme weather events can give rise to flash flooding, severe straight-line winds, and blowing dust.

Results show that the addition of lateral surface runoff increases soil moisture and latent heat throughout the model system. These affects are more pronounced in areas with high precipitation, low soil conductivity, and higher drainage area. This has the effect of increasing near surface specific humidity and atmospheric instability throughout the NAM region. This is enhancing the organization of convection at the peak of the diurnal cycle, based on spectral analysis of convective variables.