by Egline Tauya – SANF 10 No 07
The January to March 2010 climatic projections just released show more rainfall for most parts of southern Africa than in the first half of the season, October to December 2009.
The predictions are still largely consistent with the forecast of the 13th Southern African Regional Climate Outlook Forum (SACORF-13) held in August 2009.
As forecast in the SACORF 13, normal to above-normal rainfall is expected across northern half of continental SADC, Madagascar and Mauritius, with some even receiving above normal-to normal rainfall.
This covers northernmost parts of Angola, western Botswana, Democratic Republic of Congo, southern Lesotho, Malawi, northernmost parts of Mozambique, easternmost parts of Namibia, southern portions of South Africa, United Republic of Tanzania, Zambia, and northern half of Zimbabwe.
Climate experts in these regions have already provided warnings of likelihood of floods.
On the other hand, below-normal to normal with longer than normal dry spells rainfall conditions are likely in the remainder of the subregion.
In line with the earlier forecast, this covers eastern Botswana, northern Lesotho, southern Mozambique, northern South Africa, Swaziland, and southern Zimbabwe.
Areas with a high likelihood of below-normal to normal rainfall include southwest Angola, western Namibia, and south-western South Africa.
From a farming perspective, the long dry spells usually come when rainfall is most required by crops, particularly cereals and thus negatively affecting crop production.
Climate experts however point out that this update is relevant only for three-month time scales and relatively large areas.
Local to month-to-month variations may occur and users are strongly advised to contact their national meteorological and hydrological services for interpretation of the outlook (shown in detail in the map below).
The rainfall outlook was prepared by climate scientists from national meteorological and hydrological services from the SADC region as well as the Drought Monitoring Centre and the International Research Institute for Climate and Society.
In developing the outlook, experts take into account the prevailing and expected sea surface temperature anomalies over the Pacific, Indian and Atlantic Oceans as well as other factors that affect the climate of the SADC region including the Indian Downpour and atmospheric circulation processes that bring moisture into the region.
In view of these factors, the wetter than normal conditions in some parts of the region and the drier than normal in the other parts are linked to the effects of the El Niño phenomenon.
The impact of El Niño in the SADC region has varied significantly in its severity, though it generally has a greater impact in the southern half.
El Niño events have historically produced extreme weather conditions in southern Africa, that is, floods and drought.
Warmer than average conditions have persisted in the tropical Pacific since June 2009 and El Niño conditions are well established with even models projecting persistence through April/May 2010.
Sea surface temperature anomalies became positive since 2009, consistent with El Niño years.
El Niño refers to the warm phase of a naturally occurring sea surface temperature oscillation in the tropical Pacific Ocean, while La Niña refers to the cooling phase of the same sea surface temperature oscillation.
Studies of historical climate data show that the recent El Niño variation is most likely linked to global warming.
Records provide evidence that during the last four decades the number of El Niño events increased while the number of La Niña events decreased.
The former phenomenon is known to occur approximately every four to seven years, but the last four El Niños including the current one, have occurred every two to three years.
While well established, climate experts note that the current El Niño condition is rather weak and does not necessarily point to a drought in southern Africa.
Also forecast is a decrease of the El Nino conditions from 90 to 50 percent up to June 2010, when the La Niña conditions are forecast to start to increase.
Climate experts point out that below-normal rainfall does not translate to a drought neither does above-normal translate to floods. There are many climatic factors which come into play.
Above-normal rainfall is defined as being within the wettest third of historically recorded rainfall amounts while below-normal is within the driest third of rainfall amounts and normal being the middle third.
