Analysis of Atmospheric and Hydrologic Processes and Improving Streamflow Forecasts in Semi-Arid Environments with Complex Terrain

Abstract

Arid and semi-arid regions cover 40% of the Earth’s surface and inhabit 40% of the global population. Within these regions there is a need to improve our understanding of the interactions between hydrologic processes and the atmosphere. This dissertation examines these processes in the southwest US. Channel infiltration impacts the hydrologic response in semi-arid regions, diminishing streamflow and providing a source for groundwater recharge and evapotranspiration from riparian zones. We implemented a conceptual channel infiltration function in the WRF-Hydro hydrologic model. After calibration, the updated model has reduced streamflow bias within the Walnut Gulch Experimental Watershed and the Babocomari River in southeast Arizona. Accounting for channel infiltration and calibrating the model also reduces evapotranspiration errors. Calibration increased high soil moisture bias, which is an underlying limitation of the WRF-Hydro structure and calibration methodology. We also analyzed the impact of channel infiltration and calibration within 49 basins around the western US. This work showed that calibration in many of these basins results in excess baseflow compared to surface flow, which is partly due to limits of the optimization statistic and deep groundwater recharge that is not accounted for. We also consider land-atmosphere interactions in the western US. The WRF atmospheric model is coupled to the WRF-Hydro hydrologic model. Both the uncoupled WRF and otherwise identical WRF-Hydro model were executed for the 2017 and 2018 NAM seasons in. Results showed that surface and subsurface flow from WRF-Hydro increases soil moisture and latent heat. This increases the amount of instability and moisture available for deep convection, and enhances growth of NAM convection. These results indicate the role of the land surface and of lateral moisture redistribution on the lower atmosphere and for convection.