Sensitivity of the West African hydrological cycle in ORCHIDEE to infiltration processes

摘要

The aim of this article is to test the sensitivity of the West Africanhydrological cycle to infiltration processes and to riverreinfiltration pathways. This is done through sensitivity experimentsto both inputs and paramterization settings of the ORCHIDEELand-Surface Model. The parameterizations to take into account the effects of flat areas, pondsand floodplains on surface infiltration, and the effect of roots anddeep-soil compactness on infiltration are first described. The sensitivityanalysis to parameterization settings shows that the surface infiltration processes have a stronger impact in thesoudano-sahelian region and more generally in semi-arid African regions, whereas the rootzone and deep-soilinfiltration also play a role in the guinean and intermediate regions between arid and humid ones. In the equatorialand semi-humid regions, infiltration processes generally play a minor role. The infiltrationparameterizations may explain part of the difference between simulated and observed river discharge in semi-aridand intermediate basins. The sensitivity analysis to the Land-SurfaceModel inputs shows that different sources of uncertainty might also explain part of the error.Indeed, the precipitation forcing in the whole West African region, the long-term storage in thesoudano-sahelian region, the soil types in the guinean region andthe vegetation types in the equatorial region are significant sources oferrors. Therefore, observations and analyses of small scale infiltration processes aswell as continuous measurements of river discharges in West Africa areessential to ensure the reliability of futurecalibration for the infiltration parameterizations.