Effects of horizontal redistribution of surface fluxes for a coupled atmospheric and hydrologic model

Timothy M. Lahmers, Christopher L. Castro, and Pieter Hazenberg

Hydrology and Atmospheric Sciences
The University of Arizona

Evidence for surface and atmosphere coupling is corroborated in both modeling and observation-based field experiments. To evaluate these effects in the southwest US, The Weather Research and Forecasting (WRF) regional atmospheric model is coupled to the WRF-Hydro hydrologic model.

Both the uncoupled WRF and otherwise identical WRF-Hydro model are executed for the 2017 and 2018 North American Monsoon (NAM) seasons in central Arizona. In this environment, diurnal convection is impacted by precipitation recycling from the land surface. 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.

The current work assesses the impact of the representation of hydrologic processes at the land surface, in both modeling setups, and how these affect 1) local surface energy budgets during the NAM throughout Arizona and 2) the spectral behavior of diurnally driven NAM convection. Model results suggest that adding surface and subsurface flow from WRF-Hydro increases soil moisture and latent heat near the surface. This increases the amount of instability and moisture available for deep convection in the model simulations, and enhances the growth of convection at the peak of the diurnal cycle.

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