Impact of improved soil moisture on the ECMWF precipitation forecasts in West Africa

TitleImpact of improved soil moisture on the ECMWF precipitation forecasts in West Africa
Publication TypeMiscellaneous
Year of Publication2009
AuthorsAgusti-Panareda, A, Balsamo, G, Beljaars, ACM
Secondary TitleTechnical Memorandum

West Africa is a region of strong coupling between soil moisture and precipitation and where numerical weather precipitation generally exhibits poor skills. This region has been the focus of the African Monsoon Multidisciplinary Analysis - Land-surface Model Intercomparison Project (AMMA-ALMIP) in which the European Medium-Range Weather Forecasts (ECMWF) land surface scheme (HTESSEL)– among others – has been driven offline by accurate meteorological forcing in order to produce improved soil moisture estimates. This paper examines the impact of an improved initial condition for soil moisture from the HTESSEL ALMIP run on West Africa short-range precipitation forecasts with the ECMWF Integrated Forecast System (IFS). A set of forecasts covering the month of August 2006 is initialized with the soil moisture from ALMIP and compared with the operational setup. The mean difference in the soil moisture at the initial time is mirrored by differences in the evaporation and convective available potential energy in the second day of forecasts. However, it is shown that while direct and beneficial impact of a more realistic soil moisture is obtained for accumulated precipitation in the regions over the coast of the Gulf of Guinea and eastern Sahel, over the rest of the Sahel the impact is detrimental or neutral. An argument is made that the presence of convective inhibition and more complex non-local feedbacks, such as moisture convergence associated with the monsoon flow, play a more important role than the soil moisture–precipitation coupling over those regions.