Statement from the twelfth Climate Outlook Forum for the Greater Horn of Africa
                                25-27 August 2003, Nairobi, Kenya

Summary

There is increased likelihood of near-normal to below-normal rainfall over eastern and southern Tanzania, eastern and north-western Kenya, central and north-western Ethiopia, much of Somalia, parts of eastern Sudan, much of Eritrea, western Rwanda and Burundi, and extreme south-western Uganda as well as eastern and southern parts of the Lake Victoria basin. Episodic wet spells are however common during some seasons with deficient rainfall. Probabilities of near-normal to above normal rainfall favour the Red Sea coast of Sudan and Eritrea, much of southern Sudan, southern Ethiopia, parts of western Somalia much of Uganda, eastern Rwanda and Burundi, parts of western Kenya as well as northern and western Tanzania during the period September to December 2003. It may be recalled that some of these areas such as the eastern parts of Tanzania and Kenya have experienced drought conditions for the past several seasons. These areas are again anticipated to experience below normal rainfall conditions in the coming season. The impacts of the accumulated rainfall deficits may therefore be further exacerbated. It should also be noted that heavy and short duration episodic events are common even in areas forecast to receive below normal rainfall conditions.

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 near normal sea surface temperature conditions to occur in the equatorial eastern and central Pacific Ocean during the forecast period. However, colder than normal sea surface temperatures have been observed over equatorial north-western Indian Ocean and warmer than normal Sea Surface Temperatures (SSTs) have been observed over the central equatorial Indian Ocean. Warmer than normal sea surface temperatures have also been observed over the eastern equatorial Atlantic Ocean.
 
Update forecasts are provided by the National Meteorological Services (NMSs) 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 25 to 27 August 2003, the twelfth Climate Outlook Forum was convened in Nairobi, Kenya by the Drought Monitoring Centre, Nairobi to formulate consensus guidance for the September to December 2003 rainfall season in the eastern Africa sub region comprising of Burundi, Djibouti, Eritrea, Ethiopia, Kenya, Rwanda, Somalia, Sudan, Tanzania and Uganda. The sub region sometimes referred to as the Greater Horn of Africa or GHA. Users from water resources, disaster management, health, livestock, media and agriculture, among other sectors were active participants in the forum. They helped to develop the outlook and assisted in identifying the implications for the respective countries and sectors. The forum reviewed the state of the global climate system and its implications on the seasonal climate of 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.

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, empirical 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.
 

September to December 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.
 

Zone I:  Climatology is suggested over northern Sudan and north-western Eritrea.

Zone II:  Increased likelihood of near to above-normal rainfall over much of southern half of Sudan, southern Ethiopia, much of Uganda, parts of western Kenya, northern and western Tanzania as well as eastern Rwanda and Burundi.
Zone III:  Increased likelihood of near to above-normal rainfall over the Red Sea coast of Sudan, Eritrea and parts of north-eastern Ethiopia.
Zone IV:  Climatology is suggested over northern south-eastern Eritrea, parts of north-eastern Ethiopia and western Djibouti.
Zone V:  Increased likelihood of near to below-normal rainfall over eastern and southern  Tanzania, eastern and north-western  Kenya, central and north-western Ethiopia, much of Somalia, parts of eastern Sudan and much of Eritrea
Zone VI:  Increased likelihood of near to below-normal rainfall over extreme southwestern Uganda, western Rwanda and Burundi.
Zone VII:  Increased likelihood of near to below-normal rainfall over eastern southern parts of the Lake Victoria basin.

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 I), 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 emphasized that boundaries between zones should be considered as transition areas.

Contributors

The twelfth 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 Service; Somalia Republic, Sudan Meteorological Authority; Tanzania Meteorological Agency and Uganda Department of Meteorology) and climate scientists and other experts from national, regional and international institutions and organisations (Drought Monitoring Centre, Nairobi; Drought Monitoring Centre, Harare; IRI; WMO; ACMAD, National Centers for Environmental Prediction/Climate Prediction Center (NCEP/CPC), University of Nairobi, Maseno University, Sokoine University of Agriculture ,and UK Met. Office.