Estimates of Flood Inundation and Evaporation in the Niger Inland Delta Region using the JULES land-surface model

Abstract

Observed river gauging data indicate significant evaporative losses from the land and water surface in the Niger Inland delta. These losses indicate an important potential feedback between the land-surface and atmosphere. Moreover, the reduction of flow downstream of the wetland has clear implications for water management in the region and beyond. Here we have modelled the land-atmosphere coupling in the Niger Inland Delta by adding an overbank flow parameterization to the Joint UK Land-Environment Simulator (JULES) land-surface model (Blyth et al., 2002). Our hydrological model comprises a probability-distributed model of soil moisture and runoff production (PDM; Moore, 2007) coupled with a discrete approximation to the 1D kinematic wave equation to route river water downslope (G2G; Bell et al., 2007). The model was driven using data from the ALMIP experiment (Boone et al., 2006). The model simulates the broad features of the observed river flow pattern, including a downstream attenuation of the flood-wave through the wetland region. The model results illustrate significant evaporative losses from the inundated region leading to a ~10 percent reduction in river flow. The greatest relative decreases in river flow occur during spring and summer low flows. Moisture flux from the inundated region is greatly increased, accounting for up to 50 percent of the total land-atmosphere water flux during periods of maximum flooding. Moreover, a surface temperature anomaly of up to -8 K was observed in the inundated region Further work is planned to use sub-grid-resolution topographic data to improve the representation of overbank flow in the model; to compare the extents of modelled and observed inundated areas using satellite microwave remote sensing; and to include wetland evaporation process in online climate simulations to investigate land-atmosphere feedbacks