FEWS Africa Drought and Floods Hazards Assessment, 12 Dec 2002
CCA Guidance for Southern Africa Rainfall for Jan-Mar 2003 At One Month Lead
Southern Africa is defined here as the region between 10 S and 35 S; 10-50 E. The updated prediction for Jan-Feb-Mar 2003 southern Africa rainfall at one month lead (JFM.gif) is weak to moderate. Slightly higher than climatological probabilities for below normal rainfall are predicted for most of southern Africa, including northern South Africa, southern Mozambique, Zimbabwe, Namibia, and parts of Botswana, Zambia, and Angola. Slightly higher than climatological probabilities for above normal rainfall are predicted for northern Mozambique. Climatology is suggested elsewhere. Note that the current moderate El Niño event which has been strengthening over the past several weeks appears to have influenced this forecast significantly.
Over the past week, rainfall was very heavy over parts of northeastern Algeria and northern Tunisia, with weekly accumulations reaching over 100 mm in some locations and reports of 269 mm and 328 mm east of Algiers. While the low pressure systems that led to this abnormal precipitation last week continue to move over the region, rainfall totals should be lighter during the next period. Further west, in southern Mauritania and Senegal, a winter cold front brought a few millimeters to the area, but dryness relief was negligible. Heavy rains, with weekly totals exceeding 200 mm locally, fell over parts of southern Congo, western DRC, and northern Angola, and precipitation was generally heavier than normal throughout much of central Africa. Due to high river and reservoir holding capacities, flooding should not be a problem though. In southern Africa, rainfall remained lighter than normal throughout much of southern and central Mozambique, southeastern Zimbabwe, and parts of Botswana and northeastern South Africa. The region of high pressure that is contributing to this lack of rainfall also helped to bring much needed rains further away from its relative axis of rotation, as northern Mozambique and southeastern South Africa saw weekly rainfall totals up to 100+ mm locally. These rains in the southern Maize Triangle area of South Africa helped to moderate dryness, though regions to the north remain dry. Wetness was the word last week for much of southern Madagascar, eastern Kenya, and parts of southwestern Ethiopia, though lighter than normal rainfall was seen over southwestern Uganda, Rwanda, and parts of Burundi, with agriculture feeling the negative effects.
WEEKLY AFRICAN WEATHER HAZARDS ASSESSMENT STATEMENT - DECEMBER 4, 2002 DISCUSSION:
1) A severe drought last season has resulted in poor pasture conditions and moisture deficits across much of southern Mauritania. Light showers fell across the area over the preceding two weeks. However, the rain was far too light to provide any appreciable relief. Significant rains are not expected until late June/early July with the onset of the next rainy season.
2) Satellite rainfall estimates indicate below normal wet season rains across Guinea, which has resulted in lower than normal reservoir levels. Although there are no reports of drinking water shortages, the low reservoirs are causing problems for hydro electric power generation, which normally provides half of the country's electricity. This could negatively impact the highlighted hazard area and may have a ripple effect on the surrounding region. Improvement is not expected until April at the earliest. April marks the typical start of the rainy season in Guinea.
3) Dryness in recent years has resulted in poor pasture conditions and low water supplies across Ethiopia's Afar region, adjacent portions of the Tigray, Amhara and Oromiya regions, as well as parts of Eritrea and Djibouti.
4) Drier than normal conditions during October and November may have a negative impact on second season crops across much of Burundi, Rwanda and extreme southwestern Uganda. Rainfall during the first week of December continued to be spotty and lighter than normal. Scattered showers and thunderstorms throughout the period may result in some improvement.
5) Heavy rains may produce in excess of 200 mm of precipitation during the period across parts of northern Mozambique, central Malawi and Zambia. As a result, risk of flooding exists across the area, which includes the cities of Lilongwe, the capital of Malawi and Lusaka, the capital of Zambia.
6) A very dry October-November has resulted in early rainfall deficits across portions of southeastern Africa. The effects of the dryness were mitigated by cooler than normal temperatures. Recent rains have improved the overall moisture situation across the South African provinces of North-West, Freestate and parts of KwaZulu-Natal. Large deficits, however, still exist across Swaziland, southwestern Mozambique, northeastern South Africa, southern Zimbabwe and extreme eastern Botswana. Early rainfall deficits also exist across southern Malawi and Sofala, Zambezia and Tete provinces in Mozambique. Some improvement is expected across the region as the state of the atmosphere is expected to become more favorable for convection. The best chance for significant rainfall exists across northeastern South Africa, southwestern Zimbabwe, southern Malawi and central Mozambique. Southeastern Zimbabwe and southern Mozambique, however, are expected to remain mostly dry.
Author: Chester V. Schmitt