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CR 26:85-96 (2004)  -  doi:10.3354/cr026085

Downscaling of GCM scenarios to assess precipitation changes in the little rainy season (March-June) in Cameroon

Edouard K. Penlap1,2,*, Christoph Matulla1,3, Hans von Storch1, F. Mkankam Kamga2

1Institute for Coastal Research, GKSS Research Centre, Max-Planck-Straße, 21502 Geesthacht, Germany
2Atmospheric Sciences Lab, Dept of Physics, Faculty of Sciences, University of Yaoundé I, PO Box 812, Yaoundé, Cameroon
3Institute of Meteorology, University of Natural Resources and Applied Life Sciences, 1180 Vienna, Austria

ABSTRACT: Large-scale climate forcings on local precipitation in Cameroon are analysed during the little rainy season (March-June). Variables found to have strong influence are used to downscale GCM projected rainfall for 2010-2049. In particular, 2 IPCC IS92a scenarios, simulated by the ECHAM4/OPYC3 climate model, are investigated. First, monthly precipitation data from 1951-1990 at 33 meteorological stations are grouped into homogeneous rainfall regions using self-organising feature maps (SOFMs). SOFMs identified 3 groups of stations with related time-series variability. Then, an empirical orthogonal function procedure, followed by canonical correlation analysis (CCA), is used to derive statistical relationships between the homogeneous regions and large-scale variables from the NCEP/NCAR Reanalysis Project. A CCA model is established for every region. Numerous fields at different pressure levels are used as macro-scale predictors. All possible combinations of 2 predictors are systematically tested in 3 validation experiments. Those combinations that perform well in the experiments are used to derive local-scale precipitation scenarios from the general circulation model (GCM) climate projection experiments. Different combinations of large-scale variables enter the model depending on region. A composite analysis suggests that precipitation is related to an advective (convective) phenomenon in the northern (southern) part of the study domain. Moreover, precipitation changes based on 2 IS92a emission scenarios as simulated by ECHAM4/OPYC3 are calculated. The trace-gas-only and the trace-gas-plus-sulphate integrations induce changes ranging locally from +44 to -10% and from +36 to -9% respectively, relative to the 1951-1990 control period.

KEY WORDS: Cameroon · Precipitation · Regionalisation · Downscaling · Climate change

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