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Widespread extreme seasonal rains cause severe floods but improve agricultural productivity over eastern Horn

  • Seasonal Monitor
  • East Africa
  • November 30, 2023
Widespread extreme seasonal rains cause severe floods but improve agricultural productivity over eastern Horn

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  • Key Messages
  • Seasonal Progress
  • Forecast
  • Partner
    USGS
    Key Messages
    • Exceptionally heavy rains and severe flooding over southeastern Ethiopia, Somalia, and Kenya in October and November have displaced around 1.5 million people, caused human fatalities and livestock deaths, and caused significant damage to critical infrastructure, property, and crops, according to UN OCHA and government agencies. The current environmental conditions are also contributing to elevated risk of waterborne diseases and crop pests.
    • The intensity of rainfall in the October to December deyr/short rains season and impacts of associated floods have been among the worst in 40 years. In several parts of East Africa, the severity of flooding and associated impacts have been similar to or even worse than in the corresponding 1997 historic flooding event. 
    • On the other hand, the abundant rainfall has resulted in significant improvements in rangelands resources, contributing to the gradual recovery of livestock body conditions and productivity following the recent severe five-season drought (2020-2023). Cropping conditions and production prospects are currently favorable overall, despite localized damage due to floods. 
    • These extreme rains are largely attributed to the strong El Niño (+2.0 deg. C) coupled with strong positive Indian Ocean Dipole (IOD) (+1.5 deg. C) conditions and record warm sea surface temperatures in the western equatorial Indian Ocean. Overall, the strong El Niño conditions are likely to continue into early next year, with persistent unseasonal but relatively less intense rainfall expected to continue, allowing for a largely beneficial longer length of the crop growing period across much of equatorial East Africa. 
    • Forecasts for late December indicate that above-average rainfall is most likely in southern and western areas. There is an elevated risk of flooding over highly populated western, southern, and coastal sectors of East Africa. Meanwhile, in Ethiopia and Somalia (apart from the coastal regions), risk of flooding is expected to be significantly reduced.

    Seasonal Progress

    At the peak of the deyr/short rains season from around mid-October into November, much of the eastern Horn received extremely heavy rainfall. Rainfall amounts in October and November were more than two standard deviations above normal (the most extreme 2 percent of historical rainfall amounts received during this time) in southwestern and southeastern Ethiopia, northeastern and southern Somalia, much of Kenya, and coastal Tanzania, as well as in localized areas within the Lake Victoria basin, southern Burundi, northeastern Uganda, eastern DRC, and northeastern South Sudan (Figure 1).

    Figure 1

    Standardized Precipitation Index (SPI) based on CHIRPS, for October 01 – November 30, 2023
    widespread areas of above-average precipitation

    Source: UC Santa Barbara Climate Hazards Center

    Associated flooding has caused hundreds of deaths, displaced an estimated 1.5 million people in the eastern Horn (Somalia, Ethiopia, and Kenya), killed livestock and damaged crops, and destroyed property and infrastructure. The worst-affected regions include the Shabelle and Juba river basins, extending from southeastern Ethiopia into southern Somalia, and the neighboring northeastern counties of Moyale, Wajir, and Garissa in Kenya. There were also flood reports in other regions of the eastern Horn, western Uganda into eastern DRC, and parts of southern Burundi, which caused human displacement and damage to crops and infrastructure, but with relatively less severe impacts. The devastating flooding during the 2023 deyr/short rains season has been relatively comparable to the 1997 floods in southern Somalia and Kenya, but with geographic variation in terms of extent and intensity. The recent excessive rainfall and flooding, exacerbated by abnormally warmer-than-normal temperatures, is likely to drive increased spread of water-borne diseases, pests, and post-harvest losses in affected areas.

    In mid-November, flood risk based on the Basin Excess Rainfall Map (BERM) was assessed to be high to very high in Ethiopia, Somalia, Kenya, and localized areas of the Lake Victoria environs (Figure 2). In late November, the BERM has shown a southern progression of flood risk into southern and western regions of East Africa, associated with the typical seasonal shift of the Inter-Tropical Convergence Zone (ITCZ) into these regions. Consequently, flood risk in Ethiopia, Somalia, and northern Kenya is assessed to be decreasing (apart from in coastal regions), with elevated risk shifting into more populated regions of Kenya and northeastern and coastal Tanzania. 

    Figure 2

    Basin Excessive Rainfall Map (BERM) at the peak of flooding, November 11-20, 2023
    highest excess rainfall in southeastern Ethiopia and southern and central Somalia

    Source: USHS/EROS

    Overall, the abundant seasonal rainfall has also had significant beneficial impacts on equatorial East Africa’s agricultural productivity (for crops and livestock) and water resources following the five sequential failed seasons from late 2020 through late 2022. Current vegetation conditions, as evidenced by the latest eMODIS/NDVI satellite-derived product, shows exceptional improvements in general vegetation conditions, with vegetation greenness now more than 120 percent of normal across East Africa, including in many predominantly pastoral and agropastoral zones of Ethiopia, Somalia, Kenya, and northern Tanzania (Figure 3). Cropping conditions are generally reported to be favorable across most of equatorial East Africa, with crops ranging from emergence stages in southern areas to reproductive stages in southern Somalia, Ethiopia, and the western sector of the region (western Kenya, Uganda, Rwanda, Burundi, and southern South Sudan).

    Figure 3

    e-MODIS Normalized Difference Vegetation Index (NDVI), percent of the 2003-2022 median, October 21—31, 2023
    widespread above-average anomalies in areas that received heavy rainfall

    Source: USGS/FEWS NET

    The following is a country-by-country update on recent seasonal progress to date:

    • In Somalia, an estimated 2.48 million people have been affected by floods as of early December, with an estimated 118 killed and over 800,000 displaced, according to UN OCHA and local government agencies. Worst-affected have been areas along both the Juba and Shabelle rivers into lower coastal regions, according to analysis of eVIIRS satellite images of Somalia showing the geographical extent of inundated regions, corroborated by ground information. Floods were also reported in localized parts of north-central Somalia. Significant damage to infrastructure, property, and crops has been reported in most towns along the Juba and Shabelle river basins. These floods are attributed to historic heavy rains, which are among the worst in 40 years (CHIRPS climatology), with impacts reported to be worse than in 1997 and 2019 in several regions of southern Somalia. On the other hand, abundant rainfall has led to widespread regeneration of pasture and water resources for livestock production, supporting ongoing gradual recovery from the 2020-2023 drought. Ample rainfall is also supporting crop growth in areas where rainfall was not heavy enough to cause damage due to waterlogging or flooding. In flood-affected areas, off-season production prospects are also favorable once the flood waters recede. Heavy rainfall and floods are forecast to subside in the coming weeks, though risk of flooding will persist along the coastal strip in December. 

    • In Ethiopia, the overall performance of the September to November seasonal rains was characterised by well above average rainfall (exceeding 200 percent of normal) in western, southern, and eastern regions of the country, with flooding reported during the peak of the rainy season from mid-October to November. An estimated 60 people have died as of early December according to UN OCHA reporting, with more than 600,000 people displaced and livestock losses report. However, rangeland resources, livestock productivity, and cropping conditions have significantly improved in November, helping further ease the prolonged drought conditions. FEWS NET/WRSI modeling suggests favorable conditions for crop growth in the southwestern regions. The seasonal rains are likely to subside by late December. 

    • In Kenya, the short rains season has to date been characterized by cumulative rainfall of over 150 percent of the 1981-2020 average across the country, with northern, eastern, and coastal counties recording over 200 percent of average rainfall. According to UN OCHA, associated flooding has killed an estimated 60 people and displaced over 136,000 people as of November 19, with northeastern areas most affected. Meanwhile, the harvesting of long rains cereals is complete in unimodal rainfall areas in the western half of the country under favorable conditions. However, in northern Rift Valley areas, crops were harvested early to avoid the onset of the October rains despite the fact that they had not fully dried yet, which may result in post-harvest losses. Planting of short rains maize is underway in bimodal areas in the eastern half of the country as well as in the unimodal center, with concern for the impacts of heavy rainfall and flooding since early November in the eastern part of the country. Overall, impacts of flooding on the short rains agricultural production will depend on households’ abilities to recover their livelihoods and replant crops. In Kenya, above-average rainfall is expected to continue through early 2024.
    • In Sudan, conditions have been typically dry but hotter-than-normal across most of the country in November, though eastern and southern areas bordering Ethiopia and South Sudan received slightly higher-than-normal rainfall amounts. Vegetation is sparse in most northern areas of the country, as is typical. In the south, vegetation conditions are mostly drier-than-normal, with greener-than-normal conditions in localized areas that received above-average rainfall amounts. Crop production in the ongoing main harvest is likely to be below average due to the impacts of conflict, poor access to finance and inputs, and below-average and poorly distributed June to September seasonal rainfall in the south and southeast. 
    • In South Sudan, above-average off-season rainfall within the country and in the neighboring western Ethiopian highlands sustained elevated water levels in several river basins in November, resulting in flooding in riverine and low-lying areas and temporary flood-related displacement in Bor South of Jonglei; parts of Juba in Central Equatoria; Rubkona, Mayom, Leer, and Mayendit of Unity; Yirol West of Lakes; and Pibor of Greater Pibor Administrative Area. However, above-average rainfall across the country in October and November has generally supported improvement in pasture and water resources for livestock production. In late December, conditions are forecast to be typically dry but hotter-than-normal across most of the country, apart from the southern bimodal regions where above-average rainfall is expected.
    • In Uganda, cropping conditions are favorable due to ongoing above-average September to December seasonal rains, with most maize crops in reproductive stages. However, in parts of the Lake Victoria basin and western Uganda, including Hoima regions, excessive rainfall resulted in flooding in November. Forecasts indicate moderate to heavy rains will most likely persist in December, supporting favorable prospects for cropping and livestock productivity through the end of the season. Meanwhile, water levels in Lake Victoria have continued to increase. Rains are forecast to continue into early 2024, during the harvesting and drying period. Incidence of crop pests is also likely to increase with the surplus rains and hotter-than-normal conditions.
    • In Burundi, cumulative rainfall during the September to December short rains season to date has been near average across the north of the country. However, southern and eastern regions of Burundi received excessive rainfall, with flash floods reported in November. Overall, vegetation and cropping conditions are average with largely favorable agricultural production prospects for the season. Moderate to locally very heavy rains are forecast to continue through December, which could negatively affect bean crops, which are particularly sensitive to excess moisture.
    • In Yemen, rainfall has been near normal during the typical dry period which began in October, with slightly above-average rainfall amounts received in some western highland and coastal areas. Temperatures were also mostly hotter-than-normal. Current vegetation conditions, as measured by eMODIS/NDVI are mostly above normal in western areas of the country, but below normal in southern coastal areas. Rainfall in December is forecast to be limited, as is typical during the dry season.

    Forecast

    In December, weekly GEFS forecasts indicate very high probabilities of heavy rainfall amounts (>50mm per week) over southern, western, and coastal sectors of the region, with more floods likely in the coming weeks, especially in late December. Meanwhile, Ethiopia and Somalia are likely to experience a significant reduction in rainfall and associated flooding in December, apart from coastal areas.  

    Forecasts for the next two weeks indicate that cumulative rainfall for the season will likely remain significantly above average over much of the deyr/short-rains receiving areas of region through mid-December (Figure 4). Cumulative rainfall totals are expected to exceed 150 percent of long-term average amounts over much of eastern Horn and even surpass 200 and 300 percent of normal in portions of southeastern Ethiopia, northern Kenya, and southern Somalia. However, below-average cumulative rainfall is likely over parts of southern Sudan and the central highlands of Ethiopia during this period.

    Figure 4

    Anticipated cumulative rainfall for October 01 – December 15, 2023, expressed as percent of the 1981-2020 average; based on CHIRPS final data for October 01-31, CHIRPS prelim data for November 01-30, and unbiased GEFS forecast for December 01-15, 2023
    rain is forecast to be notably above normal, except for parts of northern Ethiopia

    Source: UCSB CHC

    Wetter- and hotter-than-normal weather conditions result in need to closely monitor for potential outbreaks of water-borne diseases such as malaria, cholera, livestock diseases, and crop pests, as was experienced under the almost similar climate events of 1997 and 2019. 

    According to the IRI/CPC sub-X forecast, rainfall during the December 16-29 period is likely to be above average across equatorial East Africa (Figure 5). The rest of the region is most likely to experience near-average conditions, with the northern sector expected to remain typically dry and hotter-than-normal. In Ethiopia, southwestern and some southern areas are likely to experience unseasonal above-average rainfall amounts.

    Figure 5

    IRI/CPC Sub-X rainfall probability forecast for December 16-29, 2023
    above-average rainfall is most likely across most of the region, though with relatively low probabilities

    Source: IRI/CPC

    Recommended citation: FEWS NET. East Africa Seasonal Monitor November 30, 2023: Widespread extreme seasonal rains cause severe floods but improve agricultural productivity over eastern Horn, 2023.

    FEWS NET’s Seasonal Monitor reports are produced for Central America and the Caribbean, West Africa, East Africa, Central Asia, and Somalia every 10-to-30 days during the region’s respective rainy season(s). Seasonal Monitors report updates on weather events (e.g., rainfall patterns) and associated impacts on ground conditions (e.g., cropping conditions, pasture and water availability), as well as the short-term rainfall forecast. Find more remote sensing information here.

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