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Average to above-average rainfall or well-distributed rains provide good growing conditions

  • Seasonal Monitor
  • West Africa
  • June 2, 2016
Average to above-average rainfall or well-distributed rains provide good growing conditions

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  • Key Messages
  • Update on Seasonal Progress
  • Forecasts
  • Partner
    USGS
    Key Messages
    • The onset of the long season (March to July) rains began in mid-March in the bi-modal zone and gradually expanded northward following the Intertropical Front (ITF) migration, reaching the Sudanian-Guinean zone in April and southern Sahelian zone during the first half of May.

    • Accordingly, the normal moisture conditions needed for planting began developing, as usual, in mid-March in the bi-modal areas, earlier than normal (early April) in most parts of the Sudanian-Guinean zone, and earlier than normal (early May) in the southern part of the Sahelian zone, where conditions are particularly favorable for planting.

    • Climatic conditions have generally been favorable since mid-March for normal crop development in the bi-modal and Sudanian-Guinean zones. 


    Update on Seasonal Progress
    • The ITF’s northward migration started in early March.  Its position in mid-May is between 12.5 and 16 degrees latitude. It is 1-3 degrees north of its climatological location from Mali to Chad and slightly south of its average position in a small area over western Mali and Senegal. This slightly northern position has resulted in earlier than normal rains (early May) over most of the Sahelian zone including central Chad, western Niger, northern Cameroon, Burkina Faso and Mali.
    • Over the bi-modal and the Sudanian-Guinean zones, where the growing season has been in progress for over a month, total rainfall amounts from early April to May20thvaryfrom average to above average (Figures 1 & 2) and have been favorable for crop development. Small portions of these two zones, however, have experienced light to moderate rainfall deficits, including southern Nigeria, southern Ghana, western and coastal Cote d'Ivoire and coastal Liberia. The good temporal rain distribution has offset these deficits in most areas and resulted in a timely or early start of the season (SOS) with the exception of small areas in central Nigeria, northern Cote d'Ivoire and eastern Liberia where the SOS indicates a 2-3 week delay. 

    Forecasts
    • According to NOAA/CPC’s short and medium-term forecasts, rainfall is expected to expand northward, as is seasonally normal, and will continue for the first two weeks in June without any major dry spells except in western Guinea, southwestern Mali, and northwestern Nigeria where slightly drier conditions are expected.  This forecast calls for moderate to heavy rains throughout the region where the growing season is in progress including in the southern Sahelian zone.
    • Seasonal forecasts from major meteorological centers (IRI, ECMWF, NOAA-NCEP, UKMO) for the next several three-month periods (May-July, June-August and July-September)call for above-average rainfall over most of the Sahel from Chad to eastern Mali but below-average rainfall for the bi-modal zone and the western Sahel (Senegal, Mauritania).
    • The West Africa Regional Outlook Forum known as PRESASS (Prevision Saisonnièreen Afrique Soudanienne et Sahélienne) recently released seasonal forecasts for June-August and July-September that are in agreement with the aforementioned forecasts except for in the western Sahel where the forum forecast predicts the average, below average and above average categories have equal probabilities.
    • PRESASS also made forecasts for agro-climatological parameters, which expect the following (Figure 3):
      • An early SOS (in green): southern Chad, northern Cameroon, northeastern Nigeria, central and eastern Niger, northern Burkina Faso, most of Mali and the southeastern Mauritania.
      • SOS delays over three areas (in orange): (1) most of the Sahelian zone in Chad (2) northern Nigerian states with the exception of Borno, southwestern Niger, southeastern Burkina Faso and northern Benin and (3) northern Kayes Region in Mali, southern Mauritania and northern Senegal.
      • Normal to late SOS (in yellow): southern Senegal, Guinea Bissau, southern Mali, most of Guinea, northern Cote d'Ivoire, southwestern Burkina Faso, central Nigeria, and northern parts of Ghana, Togo, and Benin.
    Figures Figure 1. Total rainfall estimate (RFE) in mm, 1stdekad of April - 2nddekad of May

    Figure 1

    Figure 1. Total rainfall estimate (RFE) in mm, 1stdekad of April - 2nddekad of May

    Source: USGS/FEWS NET

    Figure 2. Rainfall estimate (RFE) anomaly compared to the 2006-2015 mean, 1stdekad of April - 2nd dekad of May

    Figure 2

    Figure 2. Rainfall estimate (RFE) anomaly compared to the 2006-2015 mean, 1stdekad of April - 2nd dekad of May

    Source: USGS/FEWS NET

    Figure 3: PRESASS Start of seasonal forecast

    Figure 3

    Figure 3: PRESASS Start of seasonal forecast

    Source: PRESASS

    Seasonal Calendar in a Typical Year

    Figure 4

    Seasonal Calendar in 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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