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. The focus here is on runoff–infiltration partitioning and resolved overland flow. In the standard version of WRF, runoff–infiltration partitioning is described as a purely vertical process. In WRF-Hydro, runoff is enhanced with lateral water flows. The study region is the Sissili catchment (12 800 km2) in West Africa, and the study period is from March 2003 to February 2004. The WRF setup here includes an outer and inner domain at 10- and 2-km resolution covering the West Africa and Sissili regions, respectively. In this WRF-Hydro setup, the inner domain is coupled with a subgrid at 500-m resolution to compute overland and river flow. Model results are compared with TRMM precipitation, model tree ensemble (MTE) evapotranspiration, Climate Change Initiative (CCI) soil moisture, CRU temperature, and streamflow observation. The role of runoff–infiltration partitioning and resolved overland flow on land–atmosphere feedbacks is addressed with a sensitivity analysis of WRF results to the runoff–infiltration partitioning parameter and a comparison between WRF and WRF-Hydro results, respectively. In the outer domain, precipitation is sensitive to runoff–infiltration partitioning at the scale of the Sissili area (~100 × 100 km2), but not of area A (500 × 2500 km2). 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. The WRF-Hydro setup presented here shows potential for joint atmospheric and terrestrial water balance studies and reproduces observed daily discharge with a Nash–Sutcliffe model efficiency coefficient of 0.43.

The WASCAL high-resolution regional climate simulation ensemble for West Africa: concept, dissemination and assessment

“…Also, to improve the representation of the diurnal cycle of precipitation and of extreme precipitation events in the models, convectionpermitting and coupled atmospheric-hydrological modelling experiments are pursued (Arnault et al, 2016;Klein et al, 2017;Naabil et al, 2017). The climate modelling efforts presented here are undertaken in parallel to the setup of a dense network of automatic weather stations in the region with the goal of assessing and reducing model uncertainties and biases.…”

Joint atmospheric-terrestrial water balances for East Africa: a WRF-Hydro case study for the upper Tana River basin

“…These previous studies suggest that coupled atmospherichydrological modeling significantly affects the simulated atmospheric-terrestrial water balance (Maxwell et al 2011;Senatore et al 2015;Arnault et al 2016;Wagner et al 2016), especially in arid and semi-arid regions where soil moisture-precipitation interactions are largest (e.g., Findell and Eltahir 2003;Koster et al 2004;Anyah et al 2008). It is against this background that this study applies the coupled WRF-Hydro modeling system for the Mathioya-Sagana subcatchment (MSS) in the upper TRB, Kenya.…”

“…In a two-way coupling, the feedback is allowed, which leads to production of subgrid scale land surface fluxes and generally an improvement of model simulations (Zabel and Mauser 2013). It is argued that the coupled modeling approach has the advantage of including the soil moisture redistribution feedback in the lower boundary conditions of atmospheric models, which may lead to an improved representation of water and energy fluxes between land and atmosphere (Maxwell et al 2011;Shrestha et al 2014;Senatore et al 2015;Arnault et al 2016;Wagner et al 2016). Maxwell et al (2007) showed that the fully coupled modeling system yields a topographically driven soil moisture distribution and depicts a spatial and temporal correlations between surface and lower atmospheric variables and water depth.…”

“…This coupled modeling system is a recent development designed to provide more accurate information related to the spatial redistribution of surface, subsurface, and channel waters across land surfaces and more importantly as an enhancement to coupling of hydrologic models with atmospheric models. Both coupled and uncoupled WRF-Hydro systems have been applied for studies in a number of places in the world (e.g., Yucel et al 2015;Senatore et al 2015;Arnault et al 2016). Yucel et al (2015) applied the model in uncoupled mode to evaluate flood forecasting over mountainous basins in the western Black Sea region of Turkey.…”

“…Senatore et al (2015) used the WRF-Hydro in coupled mode over the Crati River basin, Southern Italy, and found that the coupled model showed better results in simulation of the water cycle components than the atmospheric model in stand-alone mode (WRF-only). Recently, Arnault et al (2016) applied the coupled WRF-Hydro for investigating the role of runoff-infiltration partitioning and resolved overland flow on land-atmosphere feedback mechanisms over West Africa and postulated the potential of such coupled modeling system in application for joint atmospheric-terrestrial water balance studies.…”