October to December constitutes an important
rainfall season over the Greater Horn of Africa sub-region. This report
provides DMCN update of the climate outlook for the September to December
2000 rainfall season for the Greater Horn of Africa that was issued at
the sixth Climate Outlook Forum held in Kisumu, Kenya from 14th to 18th
August 2000.
Among the principal factors taken into
account in developing this climate outlook update was the anticipated near
average sea surface temperatures in the tropical Pacific Ocean and the
evolving sea-surface temperature (SST) anomaly patterns over the Indian
and Atlantic Oceans. Update products from many climate centres have been
considered, including the International Research Institute for Climate
Prediction (IRI), United Kingdom Meteorological Office, National Centers
for Environmental Prediction (NCEP)/African Desk, North Carolina State
University (NCSU), and the European Centre for Medium Range Weather Forecasts
(ECMWF).
The October to December 2000 climate outlook update indicates that, there is increased likelihood of near-normal rainfall over most of the Greater Horn of Africa subregion. However, over southern Somalia, central, coastal, eastern and parts of western Kenya, northeastern Tanzania, much of Uganda and southwestern Sudan there is high likelihood of near normal to above-normal rainfall. High likelihood of near to below-normal rainfall is indicated over much of Tanzania, Burundi, Rwanda, parts of western Kenya, southwestern and northeastern Uganda, southern Sudan and southwestern Ethiopia. Climatology is indicated for much of Sudan, central and northern Ethiopia, Djibouti, much of Eritrea and extreme northwestern Somalia (see map).
It should however be noted that the rainfall distribution might be poor in many areas. For example over parts of Kenya the normal to above normal rainfall is expected in October and December, but poor rainfall performance is anticipated in November.
It should be recalled that some parts of the sub-region have experienced drought conditions for the past several seasons. In addition, the long-term mean rainfall in the arid and semi-arid parts of the equatorial eastern Africa is generally low during the season. In many of these areas therefore, the accumulated rainfall deficits may not be offset even if normal rainfall conditions are realized. Further, persistent drought has destroyed vegetation in many parts of the subregion. The projected normal to above rainfall may therefore result into increased surface runoff, soil erosion and flooding in some areas.
This forecast is relevant only for seasonal time scales and relatively large areas; local and month-to-month variations may occur. Changes have been observed in the patterns of sea surface temperature anomalies in the Indian and Atlantic Oceans over the last few weeks. These evolutions in the global SST anomalies and other general circulation patterns are being monitored, and may warrant another update to be provided by mid October. The users are strongly advised to contact the Drought Monitoring Centre, Nairobi (DMCN) and the National Meteorological Services for interpretation of this Outlook, finer details, updates and additional guidance.