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Timely start to the rainy season in the Bi-modal zone

  • Seasonal Monitor
  • West Africa
  • April 2, 2014
Timely start to the rainy season in the Bi-modal zone

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  • Key Messages
  • Update on Seasonal Progress
  • Forecasts
  • Key Messages
    • February to March rainfall estimates in conjunction with medium term forecasts indicate that the onset of the long season rains (March to July) began in the Bi-modal zone of West Africa in mid-March, as would be expected in a typical year.

    • Current climatic conditions are favorable for a normal start of agricultural activities in April in the Bi-modal zone.


    Update on Seasonal Progress
    • West Africa can be divided into four agroclimatic zones, based on seasonal rainfall amounts and patterns (figure 1). These zones, from south to north, are:
      • The Bi-modal zone which has two distinct rainy seasons: the long season (March-July) and the short season (September-November);
      • The Guinean-Sudanian zone, which has one rainy season that typically starts in April/May and ends in October/November;
      • The Sudanian-Sahelian zone, which has one season that typically starts in June and ends in October; and
      • The Saharan zone which has a very short rainy season, normally limited to few rains occurring between August and mid-September.
    • The two southern agroclimatic zones in West Africa (the bi-modal and the Guinean-Sudanian zones) are generally characterized by an agricultural system with greater crop diversification, lower levels of rainfall variability, greater levels of rainfall accumulation, and a longer rainy season. Meanwhile, the characteristics of the Sudanian-Sahelian zone (a shorter growing period, high rainfall variability and a less diversified agriculture system) bring greater risks to agricultural compared to the zones to the south. Finally, although the Saharan zone's contribution to agricultural production is very limited, its short rainy period needs to be closely monitored as high moisture levels in this zone can create favorable breeding conditions for locusts that then migrate to agroclimatic zones to the south.
    • The onset of the long season Bi-modal rains (March to July) began in mid-March, in line with climatology. These rains are beneficial to early planted yam as well as the perennial crops, such as cocoa and coffee. Most farmers in the coastal states are expected to begin planting activities for other crops the beginning of April.
    • The RFE (a remote sensing rainfall estimate) indicates that from late February to the mid-March, the Bi-modal zone (with the exception of eastern Liberia) and southern areas of the Guinean-Sudanian zone received above-average rainfall levels. This rainfall should have been particularly beneficial for yam crops, which are planted before the rainy season begins and are particularly vulnerable to dry conditions at the start of the season.
    • According to the short and medium term forecasts from NOAA/CPC, rainfall is expected to continue the next two weeks without any dry spells.
       

    Forecasts
    • ACMAD (African Center for Meteorological Applications for Development) summary forecast for the March-May period indicates below-average rainfall is to be expected over the eastern Liberia and southwestern Cote d'Ivoire, where AGRHYMET also forecasts a delayed start of the season for the same period.
    • Seasonal forecasts from major meteorological centers (IRI, ECMWF, NOAA-NCEP) for the next several three-month periods (April-June, May-July, June-August and July-September), though they have low skill this early in the season, are not showing any abnormalities that would suggest major rainfall deficits in the coming months in the rest of the region. Some of these forecasts are also indicating localized areas with increased chances of above-average rainfall.
    Figures Figure 1. Total rainfall estimate (RFE) in mm, 3rd dekad of Feb to 2nd dekad of March

    Figure 1

    Figure 1. Total rainfall estimate (RFE) in mm, 3rd dekad of Feb to 2nd dekad of March

    Source: FEWS NET

    Figure 2. Rainfall estimate (RFE) anomaly compared to the 2001-2010 mean, 3rd dekad of Feb to 3rd dekad of March

    Figure 2

    Figure 2. Rainfall estimate (RFE) anomaly compared to the 2001-2010 mean, 3rd dekad of Feb to 3rd dekad of March

    Source: FEWS NET

    Seasonal Calendar in a Typical Year

    Figure 3

    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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