Africa: Drought and floods hazards assessment 22 Jan 2004
In response to requests to continue the ITCZ analysis into Southern Africa, we attach the first Southern Africa ITCZ product from our group. While our past efforts have been more toward analyzing the Sahel region, we hope that this may provide some insight into the dekad-to-dekad circulation and convergence patterns in Southern Africa. Due to the new format, we do not have a text that compares the current features with climatology. Examination of the graphic indicates that it has evolved into a very complex feature with the main element extending from western Africa to northern Mozambique, but with an offshoot extending from central Zambia through Namibia.
Over Africa, the heaviest rainfall continued to occur over the central and southern portion of the continent extending from Gabon and Southern Cameroon to northern Namibia in the west throughout the continent to southern Kenya and South Africa on the east. Of particular importance this week was the fact that mid-Mozambique received beneficial rainfall of about 50 mm along with the area of northeast Tanzania and southeast Kenya. Lesotho received over 25 mm of rain and Swaziland about the same during this period
Madagascar continued to receive additional rainfall such that virtually the entire two-thirds of the island received greater than 50 mm for the week with some local areas over 100 mm.
Western Africa continued to indicate widespread rainfall with up to 25 mm in northeast Mali and southern Algeria.
WEEKLY WEATHER HAZARDS ASSESSMENT STATEMENT JANUARY 21, 2004 DISCUSSION:
1. The poor performance of seasonal rains in recent years has resulted in a severe multi-year drought across the Sool Plateau region of northern Somalia. The drought has resulted in severe pasture degradation and the depletion of water supplies. The next chance of significant rain will occur in April, when the main rainy season typically begins.
2. The aggregate deficits of the past two wet seasons has resulted in rainfall totals that were only 40 to 65 percent of the annual normal for the 2003 calender year across far southern parts of the Somali and Oromiya regions of Ethiopia. These dry areas extend into adjacent portions of Somalia and Kenya, too. The 2003 rainfall deficits may have resulted in degraded pastures, reduced water supplies and below normal soil and sub-soil moisture. Conditions are expected to remain dry until March, when the long rains typically begin.
3. Second season rains were much lighter than normal across much of central Kenya and eastern Tanzania. This includes much of the bi-modal crop areas of southern Kenya and Tanzania. The dry conditions may have a negative effect on pastures and may have resulted in second season crop yield reductions and failures. Moderate to heavy rains fell across southern Kenya and eastern Tanzania last week, resulting in some improvement. However, these rains likely fell too late for second season crops and moisture deficits remain in the area. Significant improvement is not expected until March/April with the onset of the long rains.
4. Hot, dry conditions during the past several seasons has resulted in severe long term drought across much of east- central and northeastern Tanzania, as well as southeastern Kenya. The drought has resulted in severely degraded pastures, very low streamflows, very low reservoir levels and greatly reduced soil moisture for second season crops. The drought in the Ruvu River Basin has left Dar Es Salaam with a water shortage. Very low dam levels in the Rufiji River Basin has greatly reduced hydroelectric power generation, requiring nationwide power rationing in Tanzania. Widespread heavy rainfall across the area Jan 15-16 resulted in some improvement and even some local flooding. However, long term drought continues as large moisture deficits remain a concern. Several weeks of soaking rains will be needed to end the drought. The next chance for steady soaking rains will occur in March and April.
5. Very dry conditions and above normal temperatures from November through mid-January have resulted in agricultural drought across central and southeastern Mozambique, as well as southern Malawi and eastern Zimbabwe. Seasonal rainfall totals are less than half of normal, with rainfall deficits from Nov 1 through the present ranging from 150 to 300 mm. Similar conditions prevailed across western Swaziland and adjacent portions of South Africa, where the past two seasons have been dry. Recent rains have eased dryness somewhat across southern Malawi and central Mozambique. The atmospheric circulation is expected to become more favorable for rainfall across southeastern Africa. Soaking rains are expected across Malawi, central Mozambique and much of Zimbabwe. Improvement is expected across these areas. Some rainfall is also possible across southern Mozambique. In Swaziland, scattered showers are expected and relief will be limited.
6. Rainfall so far this season has been only 50 to 75 percent of normal across much of South Africa's Maize Triangle, Lesotho, eastern Swaziland, parts of eastern Zimbabwe and portions of Mozambique. Across the Maize Triangle, periods of heat have increased evapotranspiration and water demands. The resulting dryness may have a negative effect on summer crops. More substantial rains are needed in order to assure a good crop season in these areas. Scattered showers are expected across eastern South Africa and Swaziland. Although moisture deficits will persist, some improvement is expected.
7. Much below normal rainfall during the 2002-03 rainy season has resulted in reduced groundwater levels, low reservoirs, low streamflows and reduced soil moisture in northeastern South Africa, Swaziland and southern Mozambique.
AUTHOR: Chester V. Schmitt