Enso signals in East African rainfall seasons

Abstract

The evolutions of ENSO modes in the seasonal rainfall patterns over East Africa are examined in this study. The udy covers the period 1961-1990. Both rotated empirical orthogonal function (EOF) and simple correlation ialyses were used to delineate a network of 136stations over East Africa into homogeneous rainfall regions in order I derive rainfall indices. Time series generated from the delineated regions were later used in the rainfall/ENSO ialyses. Such analyses involved the development of composite rainfall map patterns for EI Nino and post-ENSO + 1) years in order to investigate the associations between seasonal evolution of EI Nino-Southern Oscillation ~NSO)signals and the space-time evolution of rainfall anomalies over the region. Analyses based on both EOF and simple correlation techniques yielded eight homogeneous rainfall regions over ast Africa. The results showed unique seasonal evolution patterns in rainfall during the different phases of the NSO cycles. East African rainfall performance characteristics were stratified to identify distinct rainfall anomaly atterns associated with ENSO and post-ENSO ( + 1) years. These can be applied in conjunction with skilful long ad (up to 12 months) ENSO prediction to provide guidance on likely patterns of seasonal rainfall anomalies over Ie region. Such information can be crucial for early warning of socio-economic disasters associated with extreme iinfall anomalies over East Africa. Copyrighr'O 2000 Royal Meteorological Society.