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Above-average and well distributed rainfall in Bi-modal and Guinean-Sudanian zones

  • Seasonal Monitor
  • West Africa
  • July 22, 2014
Above-average and well distributed rainfall in Bi-modal and Guinean-Sudanian zones

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  • Key Messages
  • Update on Seasonal Progress
  • Forecasts
  • Key Messages
    • June rainfall was mostly above average and well distributed in time in the Bi-modal and the Guinean-Sudanian Zones, ensuring good maturation of first season crops.

    • Delays in pasture regeneration is to be expected in northern Senegal and southwestern Mauritania, as well as the Lake Chad region due to a combination of significant rainfall deficits recorded in June and unfavorable medium term forecast.

    • The August-October seasonal forecast calls for above-average rainfall accumulation over a large part of the region. If the recently observed Tropical Atlantic sea surface temperatures continue, the August-October period is likely to see more rain than typical.


    Update on Seasonal Progress
    • Over Mali the Intertertropical Front (ITF) progressed northward faster than normal and was north of its climatological position at the end of June. This resulted in generally above-average rainfall (Figures 1 and 2) over Mali, western Burkina Faso, Guinea, Sierra Leone, Liberia, Cote d'Ivoire and Ghana. However, it remained south of its climatological position over much of the Sahel, namely over Mauritania in the west and over eastern Niger and Chad in the east. The slowed progression of the ITF resulted in early rainfall deficits in southern Mauritania (except in Hodh el Chargui), in the regions of Tambacounda and the southern part of Saint Louis in eastern Senegal, the regions of Zinder and Diffa in Niger, Borno and Yobe States in Nigeria, and the regions of Lac, Kanem, Bahr el Ghazal, Batha Ouest, Batha Est and Wadi Fira in Chad.
    • The impact of June rainfall on agriculture differs by zone:
      • In the Bi-modal Zone crop water requirements are fully met not only over eastern Liberia, Cote d'Ivoire and Ghana where rainfall total is above normal, but also in areas of significant rainfall deficits observed in June. In areas like southern Nigeria where significant deficits were observed, the time distribution of rains has been very good and made up for the quantitative deficits.
      • In the Guinean-Sudanian Zone crop water requirements are also met everywhere including over the below average rainfall areas of Nigeria, where despite relative deficits, cumulative rainfall is sufficient for crop growth.
      • In the agricultural part of the Sudanian-Sahelian Zone conditions at the start of season indicate moisture conditions have become favorable for rainfed sowing one to three weeks earlier than normal over much of Mali and Niger. Slight delays of 1 to 2 weeks over pockets of limited size do exist, however, in the eastern part of Tambacounda in Senegal, in Seno, Oudalan and Soum provinces in Burkina Faso, in Maradi region in Niger, in Chari Baguirmi region in Chad, and in Kano, Jigawa, Yobe and Borno States in Nigeria. These areas need to be closely monitored, though at this point in time the short delays are not yet a source of significant concern.
    • The severe rainfall deficits in June in the northern part of the Sudanian-Sahelian Zone will cause delays of pasture regeneration over the pastoral areas of eastern Niger and Chad, which could contribute to delaying slightly the end of the lean season for pastoral households.
    • According to the short and medium term forecasts from NOAA/CPC, mostly moderate to heavy rainfall is expected during the second and third weeks of July over the whole region at the exception of northwestern Senegal, the Lake Chad area including Lac region in Chad, and southeastern Diffa region in Niger.

    Forecasts

    Most forecast models indicate a continued warming trend for the tropical eastern Pacific Ocean Sea Surface Temperatures (SSTs), which will transition into weak or moderate El Niño conditions during the Northern Hemisphere summer, though this is not expected to have any significant influence in rainfall pattern over West Africa. The greatest SST influence on West African rainfall will be determined by the Gulf of Guinea and Eastern Tropical Atlantic SSTs. The latest NOAA-CPC Northern American Multi-Model Ensemble seasonal forecast updated in early July calls for slightly increased chances for above-average rainfall over the following areas: an area including eastern Liberia, Cote d'Ivoire, Ghana, Togo and Benin; another area extending from Maradi and Zinder regions in Niger into Katsina, Jigawa, Yobe and Borno states in Nigeria; and southern Mali. It is also worth noting that SSTs have been constantly cooling since the end of May over the Gulf of Guinea and warming along the Guinea Bissau, Senegal and Mauritania coast. If this trend continues, it will result in a pattern that is typically related to above-average rainfall over much of the Sudanian-Sahelian zone.

    Figures Total rainfall estimate (RFE) in mm, June 2014

    Figure 1

    Total rainfall estimate (RFE) in mm, June 2014

    Source: USGS/FEWS NET

    Rainfall estimate (RFE) anomaly compared to the 2001-2010 mean, June 2014

    Figure 2

    Rainfall estimate (RFE) anomaly compared to the 2001-2010 mean, June 2014

    Source: USGS/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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