AGRHYMET Regional Center Comité permanent Inter-Etats de Lutte contre la Sècheresse dans le Sahel Permanent Inter-State Committee For Drought Control in the Sahel AGRHYMET Regional Center - BOX. 11011 Niamey (Niger) - Phone. (+227) 20 31 53 16 / 20 31 54 36 - Fax. (+227) 20 31 54 35 Web: http //www.agrhymet.cilss.int - Email : [email protected]Special Bulletin n° 2 - May 2018 I. Sea Surface Temperatures Figure 1 : State of Ocean Surface Temperatures Seasonal Forecast of the Agro-hydro-climatic Characteristics for The Sudanian and Sahelian regions of West Africa A rainy season with total rainfall amounts exceeding the 1981-2010 averages, normal to late start of the season, average to long dry spells, late to normal end of season, and above to near average flows in the major rivers is expected for most of the sudanian and the sahelian belts of West Africa and Chad An update of these forecasts will be available in mid-June and accessible at www.agrhymet.int. The forecast of sea surface temperatures (SST) from April 2018 shows neutral ENSO conditions (oscillation of temperature over the equatorial Pacific). These temperature anomalies vary from -0.5°C to 0.5°C for the period between May and July. A development towards warmer conditions in this oceanic zone, presaging an El Niño phase is expected between the months of August and October. A neutral dipole of the Indian Ocean is expected from May to July and from August to October. Near average surface temperatures are expected for the tropical Atlantic (North Atlantic and Gulf of Guinea) from May to July and August to October.
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AGRHYMET Regional Center
Comité permanent Inter-Etats de Lutte contre la Sècheresse dans le SahelPermanent Inter-State Committee For Drought Control in the Sahel
Seasonal Forecast of the Agro-hydro-climatic Characteristics for The Sudanian and Sahelian regions of West Africa
A rainy season with total rainfall amounts exceeding the 1981-2010 averages, normal to late start of the season, average to long dry spells, late to normal end of season, and above to near average flows in the major rivers is expected for most of the sudanian and the sahelian belts of West Africa and Chad
An update of these forecasts will be available in mid-June and accessible at www.agrhymet.int.
The forecast of sea surface temperatures (SST) from April 2018 shows neutral ENSO conditions (oscillation of temperature over the equatorial Pacific). These temperature anomalies vary from -0.5°C to 0.5°C for the period between May and July. A development towards warmer conditions in this oceanic zone, presaging an El Niño phase is expected between the months of August and October.
A neutral dipole of the Indian Ocean is expected from May to July and from August to October.
Near average surface temperatures are expected for the tropical Atlantic (North Atlantic and Gulf of Guinea) from May to July and August to October.
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II. Outlook of total rainfall amounts and river flows
2.1. Expected total rainfall amounts
Total rainfall amounts higher than the average of the 1981-2010 period are expected in June-July-August 2018 for the Sudanian and the Sahelian bands covering south-eastern Mauritania, eastern Senegal, the extreme Northern Guinea, the southern half of Mali, Burkina Faso (except the extreme South), Western and Eastern Niger, extreme Northern Nigeria, Central Chad and the northern parts of Benin and Togo (figure 2.1). It is very likely that this situation persist in these areas in July-August-September (figure 2.2).
Average to below average total rainfall is expected in June-July-August 2018 in the littoral zone of Senegal, in The Gambia, in Guinea Bissau, in South-Eastern Nigeria and, from July to September in Southern Guinea, westernmost part of Côte d'Ivoire, Liberia and Sierra Leone (figure 2.2). However, it is very likely that in these areas rainfall totals exceed average in July-August-September, with the exception of Guinea Bissau and Sierra Leone.
Figure 2.1: Rainfall Forecast over the period of June-July-August 2018 for the Sahel and West African countries, compared to the 1981-2010 average
2.2. Forecasts of river flows in West African river basins
The seasonal river flow forecast covers the following major river basins: Niger, Senegal, Gambia, Volta, Oueme, Mono, Comoe, Sassandra, Bandama and Lake Chad basins.
For the 2018 rainy season, river flows reaching or exceeding the average values of the 1981-2010 reference period are expected in most of the river basins of the Sudanian and Sahelian zones, except for the Benoue sub-basin where an average situation is expected. Indeed, it is expected for the river basins of Niger, Bandama (in Cote d’Ivoire), Ouémé (in Benin), Comoé (Cote D’Ivoire and Burkina Faso), the Upper Volta River and Lake Chad above-average flows. In the river basins of Senegal, Gambia, Sassandra (in Cote D’Ivoire), the lower and eastern parts of the Volta Basin flows are expected to be equivalent to or slightly greater than the averages. In the Mono Basin, forecasts are characterized by a high level of uncertainties.
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Figure 2.2: Rainfall forecast for the July-August-September 2018 period for the Sahel and West African countries, compared to the 1981-2010 average. The numbers in the small squares indicate the probabilities (in %) of having above-average totals rainfall (top), average rainfall totals (in the middle) and below average totals rainfall (bottom).
Figure 2.3: Forecast of river flows in the main river basins of West Africa for the 2018 rainy season (the average used for the comparison is that of the 1981-2010 reference period). The numbers in the small squares indicate the probabilities (in %) of having above-average (top), average (middle) and below average (bottom) flows.
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III. Forecast of the agroclimatic characteristics of the season
3.1. Starting dates of the rainy season
Equivalent to later than average starting dates of the season are expected for the entire Sudanian and Sahelian band of West Africa and Chad, except for southern Mauritania, northern Senegal and northwestern Mali, where they are expected to be average or early.
Figure 3.1: Forecast of the starting dates of the 2018 rainy season for the Sahelian and Sudanian zones compared to the 1981-2010 reference period. The numbers in the small squares indicate the probabilities (in %) of having late starting dates (top), normal starting dates (middle), and early starting dates (bottom).
3.2. Dry spells after the start of the rainy season
Longer or average dry spells are expected in the first half of the season in Niger, Burkina Faso, Mali, southern Mauritania, eastern and southern Senegal, Guinea Bissau and the northern parts of Guinea, Côte d'Ivoire, Ghana and Togo. In northern Nigeria, southwestern Chad and western Senegal, these dry spells could be equivalent or longer than the averages.
Figure 3.2: Forecast of the longest dry-spell durations after the start of the 2018 rainy season, for the Sahelian and Sudanian zones, compared to the 1981-2010 reference period. The numbers in the small squares indicate the probabilities (in %) of having longer dry spells (top), normal dry spells (middle) and shorter dry spells (bottom).
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3.3. Dry spells at the end of the rainy season
After the flowering period or the second half of the season, dry spells equivalent or longer than average are likely over the entire Sudanian and Sahelian bands, except for the northern parts of Benin, Togo and Ghana where they could rather be equivalent or shorter.
Figure 3.3: Forecast of the longest dry spell duration towards the end of the 2018 rainy season for the Sudanian and Sahelian zones, compared to the 1981-2010 reference period. The numbers in the small squares indicate the probabilities (in %) of having longer dry spells (top), normal dry spells (middle) and shorter dry spells (bottom).
3.4. Cessation dates of the rainy season
Late or average cessation dates of the season relatively to the 1981-2010 reference period are very likely for the entire Sudanian and Sahelian bands of West Africa and Chad.
Figure 3.4: Forecast of the cessation dates of the 2018 rainy season for the Sahelian and Sudanian zones compared to the 1981-2010 reference period. The numbers in the small squares indicate the probabilities (in %) of having late cessation dates of the season (top), normal cessation dates (middle) and early cessation dates (bottom).
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IV. Advices
4.1. Recommendations for risk reduction
4.1.1. With regard to drought risks
Water deficits related to the expected late start of the season in most of the sudanian and sahelian belt and long dry spells at the beginning and at the end of the season could affect the establishment of crops (risk of mortality of young shoots and reseeding), the establishment of pastures in the pastoral areas and delay the return of transhumant herds. They could also cause the persistence of high temperatures and dust storms that are favorable to the proliferation of the germs of epidemic diseases.
The expected long dry spells toward the end of the season may also be favorable to the development of some crop pests, such as the millet head caterpillar.
It is therefore recommended to take actions to avoid sowing failures, to reduce production deficits and to prevent diseases that the expected water deficits could cause in areas likely to have late starting dates and long dry spells, through:• water management, the promotion of income-generating activities, the monitoring of markets and prices
and the establishment of local security stocks,• choice of crop species and varieties that are resistant to water deficit,• use of soil water conservation farming techniques,• limitation of additional nitrogen fertilizer inputs during the crop installation periods and those at risk of
drought,• consultation of agricultural and meteorology experts in order to choose the right planting dates, to avoid
the risks of re-sowing and crop failure related to the late start of the season and the long dry spells expected in the Sahelian zone,
• interaction with meteorological, agricultural and hydrological technicians for agro-hydrometeorological information and advice on the varieties and techniques to be used,
• establishment of livestock feed stocks in risk areas, • facilitating access to the nearest water points to animals, • prevention of conflicts between farmers and pastoralists who would have difficulty moving back to the
North early, because of the likely delay in the establishment of pastures and surface water points in the pastoral zones,
• rational management of water resources for the different uses in the Benue river basin where average flows are expected as well as in the Mono basin, where the uncertain outlook requires great caution.
4.1.2.Withregardtotheriskofflooding
The above-average total rainfall amounts in the Sudanian and Sahelian bands, coupled with the likely occurrence of heavy rainfall and above-average flows in most river basins, point to a risk of flooding, particularly in river basins of Niger, Bandama, Ouémé, Comoé, Upper Volta Basin and Lake Chad Basin. As the risk of flooding is associated with both the overflow of rivers and intense rainfall, it is therefore strongly recommended to:• ensure close monitoring of alert thresholds to strengthen the anticipatory management of floods in high-
risk areas, • put in place prevention, response and recovery support mechanisms for vulnerable or affected populations,• avoid the occupation of the flood prone areas, for both cropping and housing,• prevent animals from drowning,• protect against epizootic germs that thrive under wet conditions, • strengthen collaboration between hydrological and meteorological services for the establishment and
operationalization of integrated flood risk monitoring and early warning systems, • strengthen exchanges between agencies responsible for flood monitoring and disasters risks reduction
as well as humanitarian aid agencies.
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Director of Publication :• Dr Souleymane OUEDRAOGO, General Director
Editor in Chief :• Dr Abdou ALI, Chief/Research and Information Department
Deputy editor in Chief :• Dr Issa GARBA, ME/LCD Division Manager
Editorial board :• Dr Seydou TRAORE, Agrometeorologist• Dr Agali ALHASSANE, Agronomist• Hamatan MOHAMED, Hydrologist• Issoufou MAIGARY, Hydrologist• Bernard MINOUNGOU, Hydrologist• Seydou TINNI HALIDOU, Climatologist/Météorologist• Lucie NAMODJI, Assistant in climatology• AbdoulAziz B. MAINASSARA, Acting Chief/UCID
Mise en page :• Binta ZALAGOU, PAO technician
4.1.3. Regarding the risk of diseases
In areas where a wetter season is expected, there are high levels of risk of cholera, malaria, dengue fever, schistosomiasis, diarrheal infections and Rift Valley fever for animals. It is therefore recommended to: • strengthen the prevention and response capacities of national health systems, civil protection and
nationals platforms for disasters risks reduction, through the dissemination of climate sensitive disease monitoring bulletins, the sensitization of the population and decision makers and the encouragement of collaboration between meteorological and health services,
• put in place stocks of mosquito nets, antimalarial drugs and water treatment products in areas with difficult access during the rainy season,
• monitor water quality and ensure the drainage and the cleaning of gutters,• In areas with a high probability of late start of the season and prolonged dry spells, it is recommended that
actions be taken to vaccinate populations against diseases related to the persistence of heat conditions such as meningitis, chickenpox, etc.
4.2. Recommendations to take advantage of the opportunities For areas where above average or average rainfall totals, average dry spells duration during the season and the extension of floodplains are expected, it is recommended to farmers, livestock breeders, authorities, projects, NGOs and farmers organizations, to:• invest more in improved seeds, both for food and cash crops, • develop techniques for collecting / conserving rainwater and reducing run-off in areas exposed to water
erosion, • put in place agricultural inputs (improved seeds, fertilizers and livestock feeds) in sufficient quantities in
the different zones,• apply fertilizers (organic manure and mineral fertilizer) at the recommended rates,• increase vigilance against crop pests (locusts, caterpillars, armyworms and other pests), • invest more in the exploitation of available water, by promoting irrigation, flood recession crops and
agroforestry, particularly in the flood plains of Lake Chad and the Niger basin,• support and promote the communication and use of climate information, including agrohydro-climatic
seasonal forecasts, to different users, including farmers, • set up or strengthen the farmers supervision system, monitoring and climate risk monitoring and response
mechanisms.
These forecasts are subject to change during the rainy season. It is therefore strongly recommended to pay attention to the updates that will be made in June, July and August by the AGRHYMET Regional Center, ACMAD and the National Meteorological and Hydrological Services.
