Relationship Between ENSO parameters and the Trends and Periodic Fluctuations in East African Rainfall

Abstract

The study investigated the relationship between ENSO parameters and the trends and periodic fluctuations in the East African seasonal and annual decadal rainfall. The monthly rainfall data for the period 1931–2004 was obtained from the Kenya Meteorological Department, Nairobi, Kenya while the ENSO indices data was extract from the NCEP web site. The annual and seasonal rainfall from representative stations in the all homogeneous rainfall zones over east Africa were analyzed for trends and periodicities by various statistical methods. The choice of the stations was based on the availability, continuity and length of the data set. The results from the study showed significant trends in the rainfall data over some locations. However, over most stations, there were decades in which abundant rainfall was observed while during other decades depressed rainfall was recorded. The study revealed that there is a strong link between the rainfall variability over East Africa and the ENSO parameters. Variability on decadal time scale was observed to be dominant in both rainfall and ENSO parameters, especially during the October to December season. The major cycles revealed from spectral analysis were 2 – 2.5 years, 3.6 – 4.4 years, 5 years and 10 – 12 year. Previous studies have associated these quasi-periodic fluctuations to some global phenomena such as the Quasi-Biennial Oscillation (QBO), El Niño Southern Oscillation (ENSO) and the Sunspot cycle.