Dry and wet periods in the northwestern Maghreb for present day and future climate conditions

Abstract

One urgent issue of climate research is the regional downscaling of global-scale climate scenarios. The present study, which is part of the research of the IMPETUS West-Africa project, shows an analysis of wet and dry periods in north-western Africa both from observed rainfall and from scenarios obtained from an ensemble study of the regional climate model REMO. One question is how different sources of data with different quality and different statistical characteristics can be interpreted with respect to the future development of rainfall variability. The Köppen climate classification of the very heterogeneous investigation area reveals a bias of the regional model climate scenarios towards dryer conditions. Three regions of similar rainfall variability are marked by a principal component analysis of rainfall data. For these three regions, homogenization is achieved by calculation of standardized precipitation indices (SPI). The SPI series are evaluated with respect to return times of sufficiently high/low values. For this purpose, an extreme value analysis using a fit of the generalized Pareto distribution (GPD) is compared with return values from empirical rainfall distributions. Despite the model bias, both analysis methods reveal a persistence and intensification of the observed climate shift towards shorter return times of stronger dry periods in climate scenarios under greenhouse gas forcing. © Gebrüder Borntraeger, Berlin, Stuttgart 2008.