Characterization of the Sahelian-Sudan rainfall based on observations and regional climate models
(English)Manuscript (preprint) (Other academic)
Sudan is part of the African Sahel region, which is known to be highly vulnerable to climate variability and change. However, the characteristics of observed and modeled rainfall in the country are rarely available in literature. The focus of this paper is two-fold: to analyze the rainfall aspects of Sahelian Sudan in terms of distribution of rain-days and amount, and to examine whether regional climate models can capture these rainfall features. Outputs from three regional models, namely REMO, RCA and RegCM4, have been evaluated against gridded observations and rain-gauge data from six arid and semi-arid weather stations spread across Sahelian Sudan over the period 1989 to 2008. Most of the observed rain-days are characterized by weak (0.1 – 1.0 mm/day) to moderate (>1.0 – 10.0 mm/day) rainfalls, with average frequencies of 18.5% and 48.0% out of the total annual rain-days, respectively. Although very strong rainfall events (>30.0 mm/day) occur rarely, they account for a large portion of the annual rainfall amount. The performance of the models varies both spatially and temporally. RegCM4 output is the closest to the observations in reproducing the annual rainfall cycle, especially for the more arid locations, but an unusual peak in June is present. All three models fail to capture the frequency of very strong rainfall events and, thus, underestimate the contribution of extreme rainfall events to the total annual number of rain-days and rainfall amount. Nevertheless, more moderate rainfall events from the models compensate this underestimated rainfall amount. REMO and RCA show a systematic tendency to overestimate the number of rain-days. Generally, the source of errors in rainfall modeling can be attributed to the convection parameterization in the models. This study suggests that rainfall occurring due to large-scale atmospheric circulation also contributes to the error. The present study uncovers some of the models’ limitations in skillfully reproducing the observed climate over dry regions. It will help climate and hydrological modeling communities, i.e. developers, in improving the models and also users in recognizing the uncertainties in model outputs.
regional modeling, climate model evaluation, precipitation, Sahel, TRMM, rain day analysis
Meteorology and Atmospheric Sciences
Research subject Atmospheric Sciences and Oceanography
IdentifiersURN: urn:nbn:se:su:diva-122714OAI: oai:DiVA.org:su-122714DiVA: diva2:868303