SUMMARY
There is increased likelihood of near-normal rainfall over most of the Greater Horn of Africa subregion for the period March-May, 2001. However, probabilities are favouring above-normal rainfall over Burundi, Rwanda, and most of Tanzania.
It should be recalled that some parts of the sub-region have experienced drought conditions for the past several seasons. In some of these areas, the accumulated rainfall deficits may not be offset even if normal rainfall conditions are realized.
This Outlook is relevant only for seasonal time scales and relatively large areas; local and month-to-month variations may occur. It should be noted that the formation of tropical cyclones over the southwestern Indian Ocean might influence the patterns of rainfall anomalies in the sub-region during the season. The users are 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 14 to 16 February 2001, the seventh Climate Outlook Forum was convened in Morogoro, Tanzania, by the Drought Monitoring Centre Nairobi (DMCN), to formulate consensus guidance for the March-May 2001 season in the Greater Horn of Africa (sometimes referred to as the eastern Africa sub-region, comprising Burundi, Djibouti, Eritrea, Ethiopia, Kenya, Rwanda, Somalia, Sudan, Tanzania and Uganda). Potential users were active participants in the forum. They helped develop the Outlook and assisted in identifying the implications for respective countries and sectors. The Forum reviewed the state of the global climate system and its implications for this subregion. Among the principal factors taken into account was the slightly cooler than average sea-surface temperatures (SSTs) in the tropical Pacific Ocean, and sea-surface temperature anomalies over much of the tropical Indian Ocean.
METHODOLOGY
The forum examined the evolution of the 1998-2000 La Nina episode and the current slightly cooler than average SSTs over the Pacific Ocean as well as the SST anomalies over 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-interannual forecasting, allows prediction of spatial and temporal averages, and may not fully account for all 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 centered around the climatological median; below-normal rainfall as within the driest third of rainfall amounts.
OUTLOOK
March to May constitutes an important rainfall season over the Greater Horn of Africa sub-region. The rainfall outlook for each zone within this sub-region is given below.
Zone I: Increased likelihood of near-normal to above-normal rainfall over eastern Tanzania, south-eastern Kenya and the southern tip of Somalia.
Zone II: Increased likelihood of above-normal rainfall over Burundi, Rwanda, extreme southern Uganda and southern, central, western, and northwestern Tanzania.
Zone III: Increased likelihood of near-normal to above-normal rainfall over southern Uganda and western Kenya.
Zone IV: Increased likelihood for near-normal to below-normal rainfall over central, northern and eastern Kenya, northern Uganda, extreme southern Sudan, most of Somalia, southeastern Ethiopia, and parts of northern Tanzania.
Zone V: Increased likelihood for near-normal to above-normal rainfall over southern Sudan, central and southern Eritrea, extreme northern Kenya, southwestern, central and northeastern Ethiopia, Djibouti, and extreme northwestern Somalia.
Zone VI: Climatological probabilities are indicated for southeastern Eritrea.
Zone VII: Increased likelihood for near-normal to below-normal rainfall for north-eastern Eritrea.
Zone VIII: Increased likelihood for near-normal to below-normal rainfall over central Sudan, north-western Ethiopia, and south-western Eritrea.
Zone IX: Climatological probabilities are indicated for northern Sudan and northwestern Eritrea.
MAP CAPTION
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 for the below-normal. In the case of Burundi, Rwanda, and most of Tanzania (Zone II) for example, there is 45% probability for rainfall occurring in the above-normal category; a 35% probability for rainfall in the near-normal category; and a 20% probability for below-normal category. It is emphasized that boundaries between sub-regions should be considered as transition zones.
CONTRIBUTORS
The Seventh Climate Outlook Forum was organized jointly by the Drought Monitoring Centre Nairobi (DMCN), International Research Institute for Climate Prediction (IRI), and the World Meteorological Organization (WMO) 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 forecast included representatives of
Meteorological Services from nine countries of the GHA (Institut Géographique
du Burundi; Météorologie Nationale de Djibouti; Eritrea Meteorological
Services; National Meteorological Services Agency of Ethiopia; Kenya Meteorological
Department; Rwanda Meteorological Service; Sudan Meteorological Authority;
Tanzania Meteorological Agency; Uganda Meteorological Department), METTELSAT
of the Democratic Republic of Congo and climate scientists and other experts
from national, regional and international institutions and organizations
(Drought Monitoring Centre, Nairobi; Drought Monitoring Centre, Harare;
IRI; and WMO). Additional input was supplied by the European Centre for
Medium-Range Weather Forecasts, the U.K. Met Office, and the National Centers
for Environmental Prediction.