Statement from the eleventh Climate Outlook Forum for the Greater Horn of Africa

3 to 5 March 2003, Entebbe, Uganda

There is increased likelihood of near-normal rainfall over much of Greater Horn of Africa during the period March to May 2003. Probabilities of near normal to above normal rainfall favour much of Ethiopia, Djibouti, southeastern Sudan, central and much of coastal Somalia, southeastern and northwestern Uganda, coastal and southwestern Kenya, northwestern, central, northern coast and southern Tanzania, much of Burundi and western Rwanda. On the other hand, probabilities of near to below normal rainfall favour central and southern Eritrea, northwestern and southern Ethiopia, northern and southwestern Somalia, much of Kenya and Uganda, northeastern and extreme northwestern Tanzania and eastern Rwanda. Enhanced probabilities for below normal rainfall favour southwestern Sudan, as well as southwestern and southeastern Tanzania. It should be noted that episodic intense short rainfall events are common in the sub-region even when the overall seasonal rainfall received is below normal.
 

The outlook is relevant only for seasonal time scales and relatively large areas. Local and month-to-month variations may occur. Forecast model outputs indicate that there is a high likelihood for the decay of the El Niño through the forecast period. Generally, the sea surface temperature (SST) anomalies over most of the tropical Atlantic and Indian oceans are weak. However, warmer than normal sea surface temperatures have been observed over equatorial eastern Indian Ocean. The persistence of the development of tropical cyclones in the Indian Ocean may influence the rainfall patterns in the sub-region.

Update forecasts are provided by the National Weather Services and the DMCN. The users are therefore strongly advised to keep in contact with their National Meteorological Services for interpretation of this outlook, finer details, updates and additional guidance.

The Climate Outlook Forum

From 3 to 5 March 2003, the eleventh Climate Outlook Forum was convened in Entebbe, Uganda by the Drought Monitoring Centre, Nairobi (DMCN) to formulate consensus guidance for the March to May rainfall season in the eastern Africa sub-region comprising of Burundi, Djibouti, Eritrea, Ethiopia, Kenya, Rwanda, Somalia, Sudan, Tanzania and Uganda (sometimes referred to as the Greater Horn of Africa).  Users from disaster management, water resources, health, livestock, tourism, wildlife, media and agriculture, among other sectors were active participants in the forum. They helped to develop the outlook and assisted in formulating its implications for the respective countries and sectors. The forum reviewed the state of the global climate system and its implications for the sub-region. Among the principal factors taken into account were the observed and predicted SSTs in the tropical Pacific Ocean and over much of the tropical Atlantic and Indian Oceans as well as the decaying El Niño conditions.

Methodology

The forum examined the current and expected SST anomalies over the Pacific Ocean as well as the Indian and Atlantic Oceans together with other factors that affect the climate of the sub-region. These factors were assessed using coupled ocean-atmosphere models, statistical models and expert interpretation. The current status of seasonal to inter-annual forecasting allows prediction of spatial and temporal averages and may not fully account for the physical and dynamical factors that influence regional and national climate variability.

The experts established probability distributions to indicate the likelihood of above-, near-, or below-normal rainfall for each zone (see Map). Above-normal rainfall is defined as within the wettest third of recorded rainfall amounts in each zone; near-normal is defined as the third of the recorded rainfall amounts centred around the climatological median; below-normal rainfall as within the driest third of the rainfall amounts. Climatology refers to a situation where any of the three categories have equal chances of occurring.

Outlook

March to May constitutes an important rainfall season over the equatorial parts of the Greater Horn of Africa sub-region. The rainfall outlook for each zone within this sub-region is given below.
 
 

Greater Horn of Africa Consensus Climate Outlook for the Period March to May 2003

Zone II: Increased likelihood of near to below-normal rainfall over northwestern Ethiopia, extreme eastern Sudan as well as central and southern Eritrea

Zone III: Increased likelihood of near to above-normal rainfall over northwestern Uganda, southeastern Sudan, much of Ethiopia, Djibouti, central and much of coastal Somalia, coastal parts of Kenya, and northern coast of Tanzania.

Zone IV: Increased likelihood of near to below normal rainfall over northern Somalia.

Zone V: Increased likelihood of near to below normal rainfall over southern Ethiopia, southwestern Somalia, much of Kenya and Uganda, northeastern and extreme northwestern Tanzania as well as eastern Rwanda.

Zone VI: Increased likelihood of below to near normal over southwestern Sudan.

Zone VII: Increased likelihood of near to above-normal rainfall over southeastern Uganda, southwestern Kenya, central and northwestern Tanzania, much of Burundi and western Rwanda.

Zone VIII: Increased likelihood of below to near normal rainfall over southwestern Burundi as well as southwestern and southeastern Tanzania.

Zone IX: Increased likelihood of near to above normal rainfall over southern Tanzania.

Note:

The numbers for each zone indicate the probabilities (chances of occurrence) of rainfall in each of the three categories, above-, near-, and below normal. The top number indicates the probability of rainfall occurring in the above-normal category; the middle number is for the near normal and the bottom number for the below-normal category. For example, in case of southern Tanzania (zone IX), there is 35% probability of rainfall occurring in the above normal category; 40% probability of rainfall occurring in the near-normal category; and 25% probability of rainfall occurring in the below normal category. It is emphasised that boundaries between zones should be considered as transition areas.

Contributors

The eleventh climate outlook forum for the Greater Horn of Africa was organised jointly by the Drought Monitoring Centre, Nairobi (DMCN), World Meteorological Organisation (WMO) and the International Research Institute for climate prediction (IRI) within the framework of the United States Agency for International Development (USAID) funded project, “Applications of meteorology to the reduction of climate and weather related risks to food security, water resources, and health for sustainable development in the Greater Horn of Africa sub-region”.

Contributors to this consensus climate outlook included representatives of the Meteorological Services from ten GHA countries (Insititut Geographique du Burundi; Meteorologie Nationale de Djibouti; Eritrea Meteorological Services; National Meteorological Services Agency of Ethiopia; Kenya Meteorological Department; Rwanda Meteorological Services; Somalia Department of Agrometeorology and Food Security, Sudan Meteorological Authority; Tanzania Meteorological Agency and Uganda Department of Meteorology) and climate scientists as well as other experts from national, regional and international institutions and organisations (Drought Monitoring Centre, Nairobi; Drought Monitoring Centre, Harare; International Research Institute for Climate Prediction (IRI); World Meteorological Organisation (WMO); USGS/FEWS-NET, International Research Centre on El Niño (CIIFEN), Regional Centre for Mapping of Resources for Development (RCMRD), University of Nairobi, Makerere University, Maseno University and AU/IBAR-PLP). Additional input was supplied by the National Centers for Environmental Prediction/Climate Prediction Center (NCEP/CPC), UK. Met Office, Meteo-France and the European Centre for Medium Range Weather Forecasts (ECMWRF).