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Rainfall deficits increase over parts of western and northern sector of the region

  • Seasonal Monitor
  • East Africa
  • July 31, 2023
Rainfall deficits increase over parts of western and northern sector of the region

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  • Key Messages
  • Seasonal Progress
  • Forecast
  • Partner
    USGS
    Key Messages
    • As of early August, seasonal rainfall performance was mixed for the northern and western sector of the region, with average to above-average rainfall amounts in areas of western Ethiopia, Sudan, and western South Sudan, but with increasing rainfall deficits in southeast Sudan and northeast Kenya, as well as in the rest of the long-cycle cropping (meher) areas in Ethiopia.  
    • The Sobat and Akobo basins of South Sudan are experiencing an increasing risk of flooding following persistent above-average rainfall over the western Ethiopian highlands and along the White Nile River basin, although extents are not expected to exceed typical levels.
    • Atypical hotter-than-normal conditions over most parts of eastern Horn have resulted in rapid deterioration of vegetation conditions across predominantly pastoral regions with evidence of declining surface pans and river levels.
    • According to the latest FEWS NET crop simulation models (WRSI) and available field assessments, conditions for crop growth are generally favorable across the main cereal production regions of the western and central Ethiopian highlands, Sudan, South Sudan, and in western and north rift-valley counties of Kenya. However, the Karamoja region of Uganda together with parts of southeastern South Sudan are currently experiencing mediocre to poor maize conditions.
    • The rainfall outlook for August through September is forecast to remain mixed, according to weekly GEFS, IRI/Sub-Seasonal, and NMME monthly rainfall forecasts, which depict increased likelihood of below-average rainfall amounts over parts of the northern and western sectors of East Africa, especially South Sudan and northern Uganda. However, the western Ethiopian highlands and much of Sudan are likely to maintain near-average rainfall amounts through to the typical end of the seasonal rains.

    Seasonal Progress

    Analysis of rainfall performance for June into early August for areas where this is the main rainy season indicates a concerning trend of increasing deficits, including in southeastern South Sudan and along the Rift Valley regions of southwestern-northeastern Ethiopia. On the other hand, cumulative seasonal rainfall has been average to above average in northern and western South Sudan, much of Sudan, and western Ethiopia (Figure 1).

    Figure 1

    CHIRPS cumulative rainfall, June 01– August 05, 2023, as percent of 1991-2020 average
    Map of East Africa showing CHIRPS cumulative rainfall, June 01– August 05, 2023, as percent of 1991-2020 average

    Source: UC Santa Barbara Climate Hazards Center

    These rainfall deficits are generally attributed to the weak tropical rainfall system (ITCZ), which is also largely uneven across parts of the northern and western sectors of the region causing rainfall deficits and dry spells in these regions. Similarly, mixed rainfall patterns are expected to continue in the coming weeks as depicted in Figure 2, for the period ending 20th August with increased likelihood for deepening rainfall deficits in delineated yellow to orange shaded areas.

    Figure 2

    Cumulative observed and rainfall forecast for June 01 – August 20, 2023, expressed as percent of the 1991-2020 average; based on CHIRPS prelim data for July 01 – August 05, and unbiased GEFS forecast for August 06 - 20, 2023
    Map of East Africa showing Cumulative observed and rainfall forecast for June 01 – August 20, 2023, expressed as percent of the 1991-2020 average; based on CHIRPS prelim data for July 01 – August 05, and unbiased GEFS forecast for August 06 - 20, 2023

    Source: UC Santa Barbara Climate Hazards Center

    Meanwhile, the generally average to above-average rainfall performance in central and western Sudan, western and northern South Sudan, and western and central Ethiopia has contributed to average to above-average vegetation conditions as of the end of July, as measured by the NDVI/eVIIRS vegetation anomalies (Figure 3). Notable exceptions include southeastern Sudan, southeastern South Sudan, northwestern Kenya, parts of central Ethiopia, and along the southeastern coastal areas of Somalia due to below-average seasonal rainfall and prevailing hotter-than-normal land surface conditions. In areas with typical dry seasons ongoing, including central and southern Somalia, eastern Ethiopia, and eastern and northern Kenya, abnormally dry and hot conditions have led to deteriorating rangeland resources. 

    Figure 3

    NDVI/eVIIRS Normalized Difference Vegetation Index (NDVI), percent of the 2003-2022 median, July 21-31, 2023
    Map of East Africa showing NDVI/eVIIRS Normalized Difference Vegetation Index (NDVI), percent of the 2003-2022 median, July 21-31, 2023

    Source: USGS/FEWS NET

    For the long-cycle crops that depend on the March to September seasonal rains, especially in the high to medium maize production zones of western and north rift valley counties of Kenya, the crop production prospects are near-average, based on available field assessments reports and satellite-based NDVI observations and crop simulation models. However, rain-fed sorghum and maize production in southern Somalia, southeastern lowlands of Kenya, and parts of Rwanda are likely to be below average during their ongoing harvesting and drying period, due to the erratic and below-average long-rains (March – June) season, but with relatively better conditions for recession and irrigated cropped areas along the Shabelle and Juba basins of southern Somalia. Kenya's coastal strip is also likely to experience above-average maize yields owing to the good performance of the seasonal rains over these regions.

    A moderate flood risk persists in South Sudan given high river levels and high flood extents at the start of the main rainy season. However, flooding is expected to be lower than in the last two years under forecasts for below-average rainfall in South Sudan and upstream in Uganda, as well as below-average streamflow forecasts. The White Nile River basins in eastern Sudan (Kassala and Gedaraf regions) into neighboring northeastern South Sudan face a moderate flood risk during the peak of the seasonal rains in August owing to localized persistent heavy rains over western Ethiopian highlands.

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

    • In Somalia, the overall cumulative April to June gu seasonal rainfall performance is indicative of worsening cumulative deficits over southern and parts of northern Somalia, occasioned by early cessation of the rains over southern agro-pastoral regions. Vegetation conditions are currently much drier-than-normal owing to the prevailing weather conditions with surface water pans levels on a declining trend in most parts of the country, apart from localized areas of northern Somalia. Seasonal rains are expected to subside this month into sunny and exceptional hotter-than-normal conditions, with strong winds along the coastal fishing zones of Somalia.

    • In Ethiopia, the June to September kiremt seasonal performance has largely been average to above average over western and central Ethiopian highlands. Cropping conditions are generally good to very good, with near-average national yield prospects for these high to medium agricultural productive areas. However, protracted (2020-22) and active conflict is likely to result in lower yields in the worst-affected northern regions. In the southwestern, central Rift Valley, and northeastern regions of the country, significantly below-average rainfall amounts are continuing to adversely impact on both crop and rangeland resources, exacerbated by exceptionally hotter-than-normal conditions in parts of these regions. Many areas of SNNPR are seeing rainfall deficits emerge that are making this season the driest on the historical record particularly in light of the forecast for below-average rainfall for the rest of the season. Rangeland resources are currently significantly drier-than-normal over parts of southern Oromia, Somali, and Afar regions of eastern and northeastern Ethiopia, resulting in declining surface water pans despite favorable early 2023 rainfall. Moderate to localized very heavy rains are forecast to persist over western and central highlands of the country with increased flood risks but are forecast to be below average for the rest of the kiremt-dependent areas. Both short and long-cycle meher production are likely to be below average due to ongoing sporadic conflict, lack of agricultural inputs, and moisture deficits.

    • In Kenya, cumulative rainfall from June to July in the unimodal areas in the west and part of the Rift Valley was average to above average supporting crop development. In the northwestern counties of Turkana and West Pokot, rainfall has been cumulatively well below average, negatively impacting pasture and water resources. In the southeastern marginal agricultural areas, maize is at the maturity and harvesting stages, with an above-average harvest expected in the coastal regions, but well below-average harvest prospects in the southeastern marginal agricultural areas. Along the Kenyan coastal strip very strong oceanic winds in July and August are constraining fishing activities.

    • Sudan, Kassala, Al Gedaref, and Red Sea regions are currently experiencing below-average seasonal rainfall amounts and drier-than-normal vegetation conditions. Meanwhile, most parts of the country maintained average to above seasonal rainfall performance for the past two months. Although, the cropping conditions are generally favorable based on the quality of the on-going rainfall season in most parts of the country, and very good in southern Kordofan across into western Darfur regions, the extent of cultivation and engagement in crop production has been negatively affected by the conflict either indirectly by delaying and reducing access to agricultural finance, inputs and labor, or directly by reducing access to fields in areas of heavy fighting. However, there are localized areas of mediocre maize crop conditions in parts of Kordofan. Moderate to heavy rains are expected in August in eastern and western regions of the country, but anomalous decrease in amounts in central Kordofan. There is elevated flood risk in White Nile and Sennar regions, owing to the forecast for persistent heavy rains over western Ethiopian highlands into eastern Sudan.

    • In South Sudan, rainfall as of the end of July has largely been near-average in northern and western areas, with above-average amounts in parts of Upper Nile and Unity Regions. However, parts of Eastern and Central Equatoria State have persistently experienced below-average rainfall conditions during this season, with relatively drier-than-normal vegetation and sub-optimal cropping conditions. Generally, most sorghum crops are in very good to good condition reproductive stage, apart from the northern regions which were late planted and are in vegetative phenological stages. Overall, seasonal crop production is expected to be average to below average based on the current and forecasted agroclimatic conditions at the end of the season in September. Flooding is expected within typical extents but is not likely to reach levels seen in the last two years. 
    • In Uganda, rainfall in June and July has been significantly below average in Karamoja, negatively impacting crop development in the main cultivation season. The southwestern bimodal districts of Uganda, which are currently between two rainfall seasons, have also received below-average rainfall in July. Meanwhile, the Lake Victoria basin and central districts experienced slightly above-average rainfall conditions. The rest of the country has observed near-average cumulative rainfall in July. Vegetation conditions are largely average to slightly drier-than-normal in response to the mixed rainfall performance. In southern Karamoja, vegetation conditions have been drier than average, while northern Karamoja has experienced relatively greener-than-normal vegetation. In July, parts of the Mt. Elgon region of eastern Uganda and western Kenya remain at moderate flood risk based on forecasted localized heavy rains in these regions from March to September.
    • In Rwanda and Burundi, June and July are typically part of the dry season. In Rwanda and northern Burundi, rainfall has been significantly below average during this period, with drier-than-normal vegetation. Meanwhile, Burundi experienced better season B seasonal rainfall performance, which has currently sustained near-average vegetation conditions. Typically sunny and dry conditions are forecast for the coming month, until the onset of season-A rains in September for both countries.
    • In Yemen, rainfall performance in the beginning of the July to September second rainy season has been below average. particularly in the western coastal and highlands regions of the country. Vegetation conditions are significantly drier-than-normal for much of the western sector of the country, exacerbated by the exceptionally hotter-than-normal conditions. Moderately heavy rains are forecast over western coastal regions in the coming weeks, but overall the country is expected to continue to experience below-average cumulative rainfall performance in the second rainy season.

    Forecast

    According to the latest GEFS two-week rainfall forecast (valid until late August), moderate to localized heavy rains are expected over western and northwestern Ethiopia, Sudan (Gedaraf, Sennar, White and Blue Nile, South, and western Kordofan into Darfur), South Sudan (Bahr Ghazal, Warrap, Unity, Upper Nile, across into Pibor), and parts of western Kenya and northern Uganda. However, the August rainfall IRI/Sub-X rainfall probabilistic forecasts are indicative of an uneven tropical rainfall system in the northern and western sectors of East Africa, especially in central and northeastern to southwestern Ethiopia, South Sudan, northern Uganda, and western Kenya, with possible dry spells and/or below average rainfall amounts for the forecast period, depicted in yellow to orange colors in the IRI sub-seasonal forecast. However, near average rainfall amounts are most likely within the Nile River basin.

    Light to moderate rains are expected to continue through late September over East Africa coastal strip regions, but with increasing sunny and hotter-than-normal conditions. Little or no rains are forecast for the equatorial and eastern Horn sector of the region. 

    Figure 4

    IRI Sub-X rainfall probability forecast for August 15 - 21, 2023
    Map of East Africa showing IRI Sub-X rainfall probability forecast for August 15-21, 2023

    Source: IRI/CPC

    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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