Africa: Drought and floods hazards assessment 15 Jan 2004
Update of El Niño
Sea surface temperatures remained warmer than average across most of the equatorial Pacific Ocean during December, although departures from average decreased in all of the Niño index regions during the month. Equatorial ocean surface temperatures greater than +0.5°C (~1°F) above average were found between Indonesia and 170°W and in most of the eastern equatorial Pacific between 140°W and the South American coast. Departures greater than +1°C were found between 160°E and 180°W. In spite of the slightly warmer-than-average oceanic temperatures, other indices used to monitor the state of El Niño do not indicate warm episode conditions. Over the past few months, these atmospheric indices have not shown any significant trends that would support either additional large-scale increases or any substantial decreases of SST anomalies in the equatorial Pacific.
A majority of the statistical and coupled model forecasts indicate near neutral conditions in the tropical Pacific (Niño 3.4 SST anomalies between -0.5°C and +0.5°C) through March 2004. Thereafter, the forecasts show increasing spread and greater uncertainty, during a time of the year when the skill level of all of the techniques is relatively low. NOAA's Climate Prediction Center will continue to monitor the situation. This discussion is a consolidated effort of NOAA and its funded institutions.
Over Africa, the heaviest rainfall continued to occur over the central and southern portion of the continent extending from Southern Cameroon to northern Namibia in the west throughout the continent to southern Kenya and South Africa on the east. In particular, 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 island received greater than 50 mm for the week with some local areas over 100 mm. Western Africa indicated widespread rainfall with up to 25 mm in Senegal, Mauritania and Western Sahara.
WEEKLY WEATHER HAZARDS ASSESSMENT STATEMENT JANUARY 14, 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 in 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 two past wet seasons has resulted in rainfall totals that were 40 to 65 percent of 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 seasonably 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 result in second season crop yield reductions and failures. Showers during the period are expected across southern Kenya and eastern Tanzania. Improvement, however, will be minimal.
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. Showers are expected across eastern Tanzania and southeastern Kenya. Although the rain will indeed be beneficial, only marginal improvement is expected. Several weeks of soaking rain are required to ease the impacts of the drought. Rainfall is typically light and scattered through February across southeastern Kenya and northeastern Tanzania. The next chance for steady soaking rains will occur in March and April.
5. Very dry conditions and above normal temperatures during November and December have resulted in agricultural drought across central and southeastern Mozambique, as well as southern Malawi and extreme eastern Zimbabwe. Similar conditions prevailed across western Swaziland and adjacent portions of South Africa. The unusually dry conditions have persisted into early January. Only scattered showers are expected across the region during the period. More substantial rains are possible across southern Malawi, as well as Zambezia and northern Sofala provinces in Mozambique.
6. Rainfall so far this season has been only 50 to 75 percent of normal across much of South Africa's Maize Triangle, western Lesotho, eastern Swaziland, much of eastern Zimbabwe and portions of western 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. Precipitations is expected to be scattered across the region during the period. As a result, significant improvement is not 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