Climate of Eastern Africa

Abstract

Eastern Africa, classically presented as a major dry climate anomaly region in the otherwise wet equatorial belt, is a transition zone between the monsoon domains of West Africa and the Indian Ocean. Its complex terrain, unequaled in the rest of Africa, results in a huge diversity of climatic conditions that steer a wide range of vegetation landscapes, biodiversity and human occupations. Meridional rainfall gradients dominate in the west along the Nile valley and its surroundings, where a single boreal summer peak is mostly observed. Bimodal regimes (generally peaking in April and November) prevail in the east, gradually shifting to a single austral summer peak to the south. The swift seasonal shift of the Intertropical Convergence Zone and its replacement in January–February and June–September by strong meridional, generally diverging low-level winds (e.g., the Somali Jet), account for the low rainfall. These large-scale flows interact with topography and lakes, which have their own local circulation in the form of mountain and lake breezes. This results in complex rainfall patterns, with a strong diurnal component, and a frequent asymmetry in the rainfall distribution with respect to the major relief features. Whereas highly organized rain-producing systems are uncommon, convection is partly modulated at intra-seasonal (about 30–60-day) timescales. Interannual variability shows a fair level of spatial coherence in the region, at least in July–September in the west (Ethiopia and Nile Valley) and October–December in the east along the Indian Ocean. This is associated with a strong forcing from sea-surface temperatures in the Pacific and Indian Oceans, and to a lesser extent the Atlantic Ocean. As a result, Eastern Africa shows some of the largest interannual rainfall variations in the world. Some decadal-scale variations are also found, including a drying trend of the March–May rainy season since the 1980s in the eastern part of the region. Eastern Africa overall mean temperature increased by 0.7 to 1 °C from 1973 to 2013, depending on the season. The strong, sometimes non-linear altitudinal gradients of temperature and moisture regimes, also contribute to the climate diversity of Eastern Africa.

Evaluation of Meteorological Drought and Flood Scenarios over Kenya, East Africa

“…Overall, a dry anomalous climate is experienced despite the region being situated along equatorial wet tropical belt. Circulation features associated with seasonal rainfall climatology over the region have been extensively elaborated on in past studies [37,49,[51][52][53][54][55][56][57]. Figure 1.…”

“…The highest altitude is in central highlands, while low-lying regions characterized by an ASAL climate and ecosystems occupies the eastern, northwest, and northeastern sides. Towards the south lies the Indian Ocean coastline regulating local climate, whereas the western sides of the study domain have a large water basin of Lake Victoria, driving land-lake breezes [49].…”

“…Similarly, wet events are categorized as follows: extreme (SPEI ≤ +2.00), severe (+1.50 > SPEI > +1.99), moderate (+1.00 > SPEI > +1. 49), and mild (0 > SPEI > +0.99). These values for the SPEI defines the characteristics of drought or wet conditions in terms of severity, intensity, and the duration of occurrence.…”

Evaluation of rainfall simulations over Uganda in CORDEX regional climate models

“…Eastern Uganda and some regions Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00704-018-2643-x) contains supplementary material, which is available to authorized users. close to the equator receive three rainfall seasons exhibiting a trimodal regime, with the third peak centered around July/ August due to the moisture influx from Atlantic Ocean and the moist Congo basins by the westerly winds (Mutai et al 1998;Ogallo et al 1988), and a low pressure anomaly related to a secondary convergence zone (Camberlin 2018).…”

Characterization of Historical Trends of Droughts and Pluvial Scenarios over Kenya, East Africa

“…This is of great concern to farmers who have for long rely on long rains season for planting purposes due to changes in climatic patterns. [54] and Camberlin (2018) elaborate more on general circulation features of the study domain. A summary of all datasets used is shown in Table 1 indicating the type, sources and duration.…”