Drivers and impacts of Eastern African rainfall variability

Abstract

Eastern Africa exhibits bimodal rainfall consisting of long rains (March-May) and short rains (October-December), changes in which have profound socioeconomic and environmental impacts. In this Review, we examine the drivers and corresponding impacts of Eastern African rainfall variability. Remote teleconnections, namely the El Niño-Southern Oscillation and the Indian Ocean Dipole, exert a dominant influence on interannual variability. From the mid-1980s to 2010, the long rains have tended toward a drier state (trends of −0.65 to −2.95 mm season −1 year −1 ), with some recovery thereafter, while the short rains have become wetter since the mid 1980s (1.44 to 2.36 mm season −1 year −1 ). These trends, overlain by substantial year-to-year variations, affect the severity and frequency of extreme flooding and droughts, the stability of food and energy systems, the susceptibility to water-borne and vectorborne diseases, and ecosystem stability. Climate model projections of rainfall changes differ, but there is some consensus that the short rains will deliver more rainfall than the long rains by 2030-2040, with implications for sustaining agricultural yields and triggering climaterelated public health emergencies. Mitigating the impacts of future Eastern African climate requires continued investments in agriculture, clean water, medical and emergency infrastructures, and development and adoption of adaptation strategies, as well as targeted early-warning systems driven by improved meteorological observations. Sections 2015 coincided with a weaker IOD, producing anomalies ~50% above the climatological mean 18 . However, these relationships are nonlinear, as demonstrated by extreme 2019/2020 rainfall that occurred during an anomalously positive phase of the IOD but neutral ENSO conditions 20 .The IOD and ENSO physically influence Eastern African short rains by modifying regional atmospheric circulation features (Fig. 2a,b).Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author selfarchiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.

Satellite data reveal how Sudd wetland dynamics are linked with globally-significant methane emissions

“…Our findings have profound implications for methane modelling that typically relies on static wetland data products such as GlobCover and the GLWD and therefore could lead to biases in wetland emission estimates (Bloom et al 2017, Parker et al 2020. The year-to-year variation in wetland extent of the Sudd also bears a striking resemblance to the record of global mean atmospheric growth of methane since the turn of the century, supporting previous analysis of satellite observations of methane since 2010 (Lunt et al 2019, Feng et al 2022a, 2022b, 2023. Previous work estimates that methane emissions for South Sudan, which is dominated by the Sudd, contribute to 13%-14% (3.4 Tg methane/year) of the total emissions for East Africa (25-27 Tg methane/year) between 2018 and 19 (Lunt et al 2021).…”

“…The imagery data provide new information to interpret contemporary changes in the atmospheric growth rate-in our example, year-to-year changes in the areal extent of the Sudd and surrounding wetlands are remarkably consistent with observed changes in the global atmospheric methane growth rate. This supports the idea that a large fraction of those recent annual changes in the atmospheric growth of methane are due to wetland emissions driven by changes in hydrology, particularly from Eastern Africa (Lunt et al 2021, Pandey et al 2021, Peng et al 2022, Qu et al 2022, Feng et al 2022b, 2023. The EO imagery data also represent additional information with which to constrain computational model parameters to improve the predictive capability of those models to describe hydrodynamics in continental-scale rivers.…”

Atmospheric Methane: Comparison Between Methane's Record in 2006–2022 and During Glacial Terminations

“…Zonal observations from remote stations of the NOAA network (Nisbet et al, 2016(Nisbet et al, , 2019 broadly support the findings of increased wetland emissions. Interannual rainfall and temperature variability can be very large (Lunt et al, 2021;Palmer et al, 2023;Peng et al, 2022), depending on shifts in the position and intensity of the Inter-Tropical Convergence Zone (ITCZ). Thus expansion and intensification of the tropical Hadley cell circulation can have dramatic impacts on methane emissions.…”

The Fate of Nitrogen During Agricultural Intensification in East Africa: Nitrogen Budgets in Contrasting Agroecosystems

“…Losses of fertilizer N can have cascading effects on ecosystems including emissions of the greenhouse gas nitrous oxide (N 2 O), emissions of the air pollutant precursors nitric oxide (NO) and ammonia (NH 3 ), and leaching of nitrate ($${{\mathrm{N}\mathrm{O}}_{3}}^{-}$$) to groundwater, with negative impacts on soils, water, and biodiversity (Galloway et al., 2003; Tilman et al., 2002). Further, climate change is expected to alter rainfall regimes across SSA (Cook et al., 2020; Palmer et al., 2023), which may alter both crop productivity and N fluxes as leaching losses and gaseous emissions are linked to moisture levels and movement in soils.…”