CMIP5 simulated climate conditions of the Greater Horn of Africa (GHA). Part 1: contemporary climate

Abstract

The present study is a preliminary interrogation of the ability of ten Earth System Models (ESMs) from the fifth phase of coupled model intercomparison project to characterize seasonal and annual mean precipitation cycle over the Greater Horn of Africa region. Each ESM had at least 2 ensemble members. In spite of distributional anomalies of observations, ESM ensemble means were examined on the basis of gridded precipitation data. Majority of the ten ESMs analyzed correctly reproduce the mean seasonal and annual cycle of precipitation for the period 1979-2008 as compared to gridded satellite-derived observations. At the same time our analysis shows signif- icant biases in individual models depending on region and season. Specifically, a modest number of models were able to capture correctly the peaks of bimodal (MAM and OND) and JJAS rainfall while a few either dragged the onset to subsequent months or displaced the locations of seasonal rainfall further north. Nearly all models were in agreement with their representation of the zonal orientation of spatial pattern of the leading EOF rainfall modes; more so, enhanced precipitation over the Indian Ocean and a dipole mode of precipitation pattern are captured in the first and second mode respectively. Further, the corresponding EOF time series of the ESMs rainfall modes were all in phase with observations. However, all models output were posi- tively biased against observations, with large medians and varied range of anomalies. Therefore, caution needs to be taken when choosing models for applications over the region, especially when ensemble means have to be considered.