Climate and climatic variability of rainfall over eastern Africa

Abstract

This review examines several aspects of the climate of eastern Africa. The climatic commonality throughout the region is the frequent occurrence of drought severe enough to incapacitate the population. Because of recent droughts and evidence of disastrous, long‐term climatic change, the region has become a major focus of meteorological research. This review covers six relevant topics: climatic regionalization, seasonal cycle, intraseasonal variability, interannual variability, recent trends, and seasonal forecasting. What emerges is a markedly different view of the factors modulating rainfall, the dynamics associated with the seasons, and the character of teleconnections within the region and the interrelationships between the various rainy seasons. Some of the most important points are the following. (1) The paradigm of two rainy seasons resulting from the biannual equatorial passage of the Intertropical Convergence Zone is inadequate. (2) The “long rains” should not be treated as a single season, as character, causal factors, and teleconnections are markedly different in each month. (3) The long rains have been declining continuously in recent decades. (4) The Madden‐Julian Oscillation has emerged as a factor in interannual and intraseasonal variability, but the relative strength of Pacific and Indian Ocean anomalies plays a major role in the downward trend. (5) Factors governing the short rains are nonstationary. (6) Droughts have become longer and more intense and tend to continue across rainy seasons, and their causes are not adequately understood. (7) Atmospheric variables provide more reliable seasonal forecasts than the factors traditionally considered in forecast models, such as sea surface temperatures and El Niño–Southern Oscillation.

Skill of ECMWF system‐4 ensemble seasonal climate forecasts for East Africa

“…Northern parts (Ethiopia) exhibit a unimodal rainfall patterns with one season from June to September. Large parts of Kenya and northern Tanzania experience a bimodal pattern receiving its rainfall in MAM, and OND, while western Kenya and the coastal regions exhibit a tri-modal pattern experiencing rainfall in MAM, JJA and OND seasons (Nicholson, 1996(Nicholson, , 2014Indeje et al, 2000;Korecha and Barnston, 2007;Gitau et al, 2015).…”

“…Bias characteristics in each season may be due to rainfall causing mechanisms associated with regional and local features as opposed to large-scale features that influence OND and JJA seasons (Nicholson, 1996(Nicholson, , 2014Camberlin et al, 2001;Camberlin and Philippon, 2002;Ogwang et al, 2014). These could be the influence of water bodies, topography or other meso-scale forcings and their interaction with large-scale mechanisms (Indeje et al, 2000).…”

Effect of Climate Change on Reliability of Rainwater Harvesting Systems for Kabarole District, Uganda

“…However, with a warmer and drier climate predicted for Southern Africa, an increased frequency and intensity of El Niño events is expected [3]. In a review of climate dynamics and variability across East Africa, Nicholson reports that rainfall across East Africa has strong links to the El-Nino Southern Oscillation (ENSO) phenomena with above average rainfall recorded during ENSO years [4]. Shongwe et al [5] also reports that for East Africa, an increase in mean precipitation rates and intensity of high rainfall events and less severe droughts is expected.…”

Reconstruction of Late Pleistocene Paleoenvironments Using Bulk Geochemistry of Paleosols from the Lake Victoria Region

“…Today there is very little annual variability in temperature at Lake Victoria (Nicholson, 1996). Precipitation, however, varies considerably and is controlled by the location of the Intertropical Convergence Zone (ITCZ), which crosses Lake Victoria twice a year, creating rainy seasons in March and in October (Nicholson, 1996).…”