ANALYSIS OF PRECIPITATION BASED ON ENSEMBLES OF REGIONAL CLIMATE MODEL SIMULATIONS AND OBSERVATIONAL DATABASES OVER ETHIOPIA FOR THE PERIOD 1989–2008

This study examines the performance of multi-model numerical simulations and multiobservational
databases focusing on seasonal cycles and spatial variations in precipitation over
Ethiopia. Seven Regional Climate Models (RCMs) driven by the ECMWF Interim reanalysis
(ERA-Interim) and generated in the framework of COordinated Regional climate Downscaling
EXperiment (CORDEX) project, and four observational databases computed using different
interpolation techniques and blending strategies, were evaluated against typical observational
database produced by Climate Research Unit (CRU) over Ethiopia on monthly basis. All were
produced at 48.8 km grid resolution for the period 1989–2008. The preliminary results showed
that ensembles (multi-model ensemble (MME) + multi-observational ensemble (MOE)) were as
good as CRU in reproducing the temporal variability and the geographical distribution of
precipitation. Comparison of seasonal means and temporal correlation results revealed that
there were good agreements between ensembles and CRU at each grid point and in close
proximity to each other. Results of rotated principal components (RPCs), rotated empirical
orthogonal functions (REOFs), and the associated power spectra showed that every ensemble’s
element was able to simulate the seasonal cycles and homogeneous precipitation zones of CRU
reasonably well. Excessive and deficient rainfall periods, which were seen in every ensemble’s
RPCs, matched up CRU historical records.