Extended Abstract

(d)2.5 4.0 5.5(c)-10 0 10(b)-10 0 5(a)0 40 80 1401962 1967 1972 1977 1982 1987 1992 1997Time(Years)Figure 1: Components of daily rainfall at Dagoretti station for 1962-2000. (a) high frequency component; (b)MAC component; (c) interannual component; and (d) decadal-to-trend component.The coastal region of EEA also receive rainfall in most parts of the year due to the effect of the IndianOcean. Figure 2(b) of the corresponding EOF1 PC series shows that the annual cycle is not strictlyregular in frequency or amplitude indicating a changing annual cycle of rainfall. The spatial patternfor the EOF2 (with variance of 24%) and its corresponding time-series (not shown) depicts significantpositive loadings over parts affected by the local circulation systems. The remaining parts of theregion exhibit weak loadings implying weaker effect of local systems in the annual cycle. Again as inEOF1, the EOF2 series indicates the modulation of the annual cycle with some years having strongeramplitude of annual cycle.3.1.2 Interannual VariabilityFigure 3 shows the pattern of the first eigenvectors (EOF1) of the monthly interannual rainfallcomponets and its corresponding PC series. The first and second patterns account for 30% and 8% ofthe total variance. The first EOF pattern (Figure 3a) is positive in most parts of the region except thenorthwestern, and western parts of Uganda that has weak negative signal. The highest values areconcentrated in the eastern parts of the region. The loading patterns for MAM and OND (figures notshown) were generally simmilar with those of monthly series, with only slight differences. Thecorresponding first PC time series for the interannual component (Fig. 3(b)) shows variationsthroughout the data span. The periods with maxima values all coincided with warm ENSO eventsexcept Jul 1961 – May 1962 and Sep 1967 – Aug 1968. These two periods however coincided withthe build up of positive anomalies over the Indian Ocean (positive Indian Ocean Dipole). For theyears with minima values, two periods i.e. Sep 1964 – Jul 1965 and Oct 1998 – May 2000 coincidedwith the cold ENSO events while the others coincided with neutral ENSO phase. These resultsindicate that the first EOF of the interannual component for EEA is consistent with ENSOand Indian Ocean SST variability. The major warm ENSO events correspond to the highpeaks of the time series especially for the OND season. The ENSO event of 1997 is howeverdistinctly conspicuouse in all the first EOF PCS series for three cases considered.-281-