Drivers and impacts of Eastern African rainfall variability
Seasonal rainfall is integral to the 457 million people living across Eastern Africa, a region including Burundi, Djibouti, Eritrea, Ethiopia, Kenya, Rwanda, Somalia, South Sudan, Sudan, Tanzania and Uganda (Box 1). The number, duration and timing of these rainfall seasons varies, driven principally by the movement of the intertropical convergence zone (ITCZ)1. For instance, the most northerly and southerly regions (northern Ethiopia, Eritrea, Sudan, South Sudan and southern Tanzania) experience a single summer wet season for their respective hemispheres. In contrast, countries between these latitudinal extremes (encompassing Kenya, Uganda, Somalia, Burundi, Rwanda and parts of northern Tanzania and southern Ethiopia) experience two wet seasons. These two wet seasons occur during boreal spring (typically March–May, MAM; the more intense long rains) and autumn (typically October–December, OND; the less intense short rains), although there are substantial regional variations in these timings.
This seasonal rainfall is vital to the health and economic prosperity of the region. For example, long rains support agricultural production and thus national food security. Rain-fed agriculture, in turn, has a substantial role in the economy of many Eastern African countries. Agriculture employs 67% of people in Ethiopia, 80% in Somalia, 54% in Kenya, 63% in Eritrea and 38% in Sudan2. Agriculture also represents an extensive contribution to the annual multibillion-dollar export of goods such as sugar, tea, coffee, tobacco, nuts and seeds, cut flowers and vegetables3. Moreover, rainfall is pivotal to energy production, particularly given that hydropower represents a large fraction of electricity generation in Eastern Africa4. Aquifer recharge from rainfall5,6 also provides a sustainable reservoir of groundwater for potable water (and irrigation) during periods of drought5, demonstrating the importance of rainfall for water security, especially when looking to the future7.
Observed rainfall variability, particularly disruption to the long and short rains, can therefore result in a wide range of humanitarian, economic and environmental impacts. For example, three anomalously low rain seasons over Somalia from April 2016 to December 2017 resulted in sustained and widespread drought conditions that led to considerable losses of agricultural crops and livestock8. Consequently, more than six million people faced acute food shortages and malnutrition9, exacerbated by a shortage of potable water that led to disease outbreak. A similar situation unfolded in 2022 (refs. 10,11) following poor rain seasons since late 2020. In stark contrast, consecutive anomalously high rain seasons over South Sudan since 2019 led to prolonged flooding, directly affecting more than 900,000 people12 each year. Recurrent flooding further damaged water treatment facilities, leaving millions without potable water and resulting in the outbreak of water-borne diseases12. Moreover, fields that typically support subsistence farming are submerged by floodwater, reducing the land available for cultivation, and so affecting crop yields13 and livestock productivity14. To help to mitigate such impacts and inform future adaptation changes, it is therefore vital to fully understand all aspects of Eastern African rainfall, particularly in light of continued changes arising from anthropogenic warming15.
Article source: https://www.nature.com/articles/s43017-023-00397-x