Journal of Kenya Meteorological Society
Decadal Rainfall Variability Modes in observed Rainfall Records over East Africa and their Predictability using Sea Surface Temperature
Philip Omondi*, Laban A Ogallo*, Raphael E. Okoola**
IGAD climate Prediction and Applications Centre*, Department of Meteorology, University of Nairobi, Nairobi, Kenya**
IGAD climate Prediction and Applications Centre
P.O. Box 10304 00100, Nairobi, Kenya
(Manuscript received 23 March 2009, in final form 02 July 2009)
The space-time patterns of decadal rainfall variability modes over East Africa and their predictability potentials using Sea Surface Temperatures (SST) are investigated. The analysis includes observed rainfall data from 1920-2004 and global sea surface temperatures (SSTs) for the period 1950-2004. Simple correlation, trend and cyclical analyses, Principal Component Analysis (PCA) and Canonical Correlation Analysis (CCA) methods are employed. The results show decadal signals in filtered observed rainfall record with 10 years period during March – May (MAM) and October – December (OND) seasons. During June – August (JJA), however, cycles with 20 years period are common. Too much / little rainfall received in one or two years determines the general trend of the decadal mean rainfall. PCA results showed six, five and four modes of variability accounting for 80%, 81.3% and 65.1% during MAM, OND and JJA seasons respectively. CCA results for MAM showed significant positive correlations are observed between the sea surface temperatures and the canonical component time series over the central equatorial Indian Ocean. Positive loadings are spread over the coastal and Lake Victoria regions while negative loadings over the rest of the region with significant canonical correlation skills. For the June – August season, Atlantic SSTs had negative loadings centred on the tropical western Atlantic Ocean associated with the wet / dry regimes over western/eastern sectors. The highest canonical correlation skill between OND rainfall and the Pacific SSTs showed that ENSO/La Nina phases are associated with wet/dry decades over the region.