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Average to above average cumulative seasonal rainfall despite localized early-season deficits

  • Seasonal Monitor
  • West Africa
  • October 16, 2018
Average to above average cumulative seasonal rainfall despite localized early-season deficits

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  • Key Messages
  • UPDATE ON SEASONAL PROGRESS
  • FORECASTS
  • Key Messages
    • The 2018 growing season in West Africa has been characterized by globally average to above average rainfall (Figure 1). However, some areas were affected by below average rainfall with pockets of severe and prolonged dryness in northwestern Senegal and southwestern Mauritania (Figure 2).

    • The severe rainfall deficit and very long dry spells that northern Senegal and southwestern Mauritania experienced from early to mid-season are likely to have a serious impact on crop and range performance (Figure 3 and Figure 4).

    • The ITF continues its southward retreat (Figure 5). Its location at the first dekad of October indicates a timely end of the growing season in the northern part of the Sahelian zone.

    • The medium-term forecast for the next two weeks (October 22nd – October 29th) calls for light to moderate rainfall over the Gulf of Guinea countries while the rest of the region will be dry.


    UPDATE ON SEASONAL PROGRESS
    •  The Intertropical Front (ITF) continues its southward retreat, leaving the northern half of the Sahelian zone to the dry season.  It is currently at its climatological position in Mali, Mauritania and Senegal, and slightly north of it in Niger and Chad (Figure 5).
    • Both the major and minor seasons in the bi-modal zone have been very good and an average to above average harvest is expected.  Based on the medium-term forecast, moderate to heavy rainfall is expected through the rest of October which will be very beneficial to crops for the remaining part of the minor season.
    • For the rest of the Sudanian-Guinean zone, outside of the bi-modal zone, rainfall during the growing season has also been generally good.  Despite the rainfall deficits experienced early in the season in June-July in western Liberia, Sierra Leone and southwestern Guinea the season outcome is expected to be at least average based on the good agro-climatological conditions that have prevailed from the end of dryness to present.
    • Most of the Sahelian zone received adequate and well distributed rainfall throughout the season. Most of the areas affected by the June-July rainfall deficits and bad time distribution of rainfall, such as western Niger and eastern Burkina Faso, experienced significant improvement in agrometeorological conditions following the mostly average to above average rainfall received in the second dekad of July.  Consequently, a close to average harvest is expected.
      • For southwestern Mauritania and northwestern Senegal, the July relief was short-lived.  The area continued to suffer from dry conditions that persisted until mid-August (Figure 2), but conditions significantly improved afterward.

    FORECASTS
    • The short and medium-term NOAA/CPC forecasts call for moderate to heavy rains over the Gulf of Guinea countries.
    • The November seasonal forecast from NOAA-NCEP calls for a slight increase in likelihood of above average rainfall over southern Nigeria, southwestern Ghana, most of Cote d’Ivoire, and the southeastern tip of Guinea.
    Figures Map showing total (1st dekad of April – 1st dekad of October) rainfall estimate (RFE) anomaly, compared to the 2007-2016 mean

    Figure 1

    Figure 1. Total (1st dekad of April – 1st dekad of October) rainfall estimate (RFE) anomaly, compared to the 2007-2016 mean

    Source: USGS/FEWS NET

    Map showing Areas affected by long dry spells and rainfall deficit from 21 July – 20 August: southwestern Mauritania, norther

    Figure 2

    Figure 2. Areas affected by long dry spells and rainfall deficit from 21 July – 20 August

    Source: USGS/FEWS NET

    Map showing West Africa eMODIS 250m Percent of Median NDVI: average to above average across most of the region except in sout

    Figure 3

    Figure 3. West Africa eMODIS 250m Percent of Median NDVI

    Source: USGS/FEWS NET

    Graph showing the NDVI profile for Wilaya of Gorgol Mauritania. 2018 NDVI is significantly below the curve for the median fro

    Figure 4

    Figure 4. NDVI profile - Wilaya of Gorgol Mauritania

    Source: USGS/FEWS NET

    Map showing the ITF position during the first dekad of October. ITF is similar to the previous dekad and also similar to the

    Figure 5

    Figure 5. ITF position during the first dekad of October

    Source: USGS/FEWS NET

    Title: West Africa seasonal calendar Description: In the North, Main season cultivation is from mid-May to mid-August. Main h

    Figure 6

    SEASONAL CALENDAR FOR A TYPICAL YEAR

    Source: FEWS NET

    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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