Role of Runoff-Infiltration Partitioning and Resolved Overland Flow on Land-Atmosphere Feedbacks: A Case-Study with the WRF-Hydro Coupled Modeling System for West Africa

Abstract:

The analysis of land-atmosphere feedbacks requires detailed representation of land processes in atmospheric models. Our focus here is on runoff-infiltration partitioning and resolved overland flow. In the standard version of the Weather Research and Forecasting (WRF) model, coupled with the Noah Land Surface Model, runoff-infiltration partitioning is described as a purely vertical process. In the WRF-Hydro coupled modeling system, runoff is enhanced with lateral water flows. The study region is the Sissili catchment (12800 km2) in West Africa, and the period of investigation is March 2003 - February 2004. Our WRF setup includes an outer and inner domain at 10 and 2 km resolution, respectively. In our WRF-Hydro setup the inner domain is coupled with a sub-grid at 500 m resolution to compute overland and river flow. Model results are compared with TRMM precipitation, MTE evapotranspiration, CCI soil moisture, CRU temperature, and streamflow observation. In the outer domain, a sensitivity analysis to runoff-infiltration partitioning gives a range of simulated annual precipitation of one sixth of the annual amount. In the inner domain, where precipitation patterns are mainly prescribed by lateral boundary conditions, sensitivity is small, but additionally resolved overland flow here clearly increases infiltration and evapotranspiration at the beginning of the wet season when soils are still dry. Our WRF-Hydro setup shows the potential of this fully coupled modeling system for joint atmospheric and terrestrial water balance studies, and reproduces observed daily discharge with a Nash-Sutcliffe model efficiency coefficient of 0.43.