Africa: Drought and Floods Hazards Assessment: 24 Jul 2003
Update of the ITCZ Position
From July 11-20, 2003, the African portion of the Intertropical Convergence Zone (ITCZ) slowed its overall northward movement, and was located near 18.2 degrees north latitude when averaged over the domain from 15W-35E longitude. This places the ITCZ around 0.4 degrees north from its position during the first ten days of July; a small movement compared to the previous progression of around 1.1 degrees northward. Although much of the Sahelian region saw little movement of the ITCZ from the previous dekad, the region from 15W-0E saw a jump northward due to stronger than normal southerly winds pushing into the area. These winds from the south helped to spread rainfall throughout much of the western Sahel as evident in increased ten-day total precipitation into Guinea, Cote d'Ivoire, Liberia, and Ghana. Rainfall during the current dekad was lighter, though, in parts of southern Mali and in Burkina in western Africa. In the east, rainfall was generally similar to the first dekad of July. The eastern region (from 20-35E) shows a smaller northward bias of around a degree for the current period. Both western and eastern region ITCZ average positions have already reached their normal maximum northward extent, almost a month earlier than normal.
Although widespread showers covered Ethiopian crop areas, estimated amounts remained below normal in north central, central, and southwestern areas during the past week. The area of below-normal rains extended northward into parts of Eritrea. Cumulative rainfall since June 1 may be as low as 40 percent of normal from southern Eritrea southward into central Ethiopia, based on satellite estimates. Elsewhere, increased rains eased dryness along the coast of the Guinea Gulf in West Africa, but amounts remained light (10 mm or less) along the immediate southern coast of Cote d'Ivoire. Rainfall picked up dramatically along the western coast from Senegal to Liberia. Over 50 mm of rain fell in the western groundnut basin of Senegal, relieving dryness there. Significant rainfall deficits continued, however, across interior Senegal into southwestern Mauritania. Excessive rains, locally exceeding 100 mm, hit several areas in the Sahel, including eastern Burkina Faso and southeastern Chad.
AFRICA WEATHER HAZARDS TEXT EXPLANATION
VALID JULY 24-30, 2003
1) A severe drought last season has resulted in poor pasture conditions and moisture deficits across much of northern Senegal, southern Mauritania and adjacent portions of Mali. Over much of the southern hazard area, which is shown by the yellow hatching, beneficial rains have fallen over the past several weeks. One exception to this is over northern Senegal, which has been highlighted by the red hatching. Rain showers have continued to move northward within the general hazard area, which will help to alleviate some of the long-term deficits.
2) Over the past several weeks, beneficial rains have fallen in areas just on the east side of Lake Tana. In general, rains over the hazard region that extends from the northeastern highlands southwestward into southern Sudan have been slow to start. Forecasts indicate that there is a potential for some beneficial rainfall along the southern and eastern portions of the hazard region during the next week. This area will continue to be watched closely as long-term deficits will be magnified if seasonal rains do not begin soon.
3) A multi-year drought over northern Somalia has affected pasture lands over the region. This has especially stressed the Sanag and Sool regions. Field reports indicate that herders are moving livestock out of the regions due to deteriorating land. Water supplies may also be affected in and around the region. According to climatology over the area, the next opportunity for significant rainfall will be in September.
4) Areas along the Somalia coast will be watched for short-term dryness. Most of this region averages around 20 mm per week, however, over the past several dekads little rain has fallen. Crops grown along the coastal region may be negatively affected. Little rainfall is forecast for the upcoming week.
5) Rainfall totals during the 2002-2003 wet seasons were less than half of normal across much of Swaziland, northeastern South Africa and the southern most provinces of Mozambique. This includes significant portions of the Limpopo River Valley. Precipitation deficits of 150 to 400 mm have raised concerns over water shortages across the region.
6) Over past dekads, little rainfall had forced central areas of Cote d'Ivoire and Ghana into a flash drought; however, during the last period, significant showers brought beneficial rains to the hazard region. The area should recover as some showers produced up to 100 mm of rain. Forecasts indicate that rains should continue throughout the impending period.
7) Seasonal rainfall amounts in Liberia, Sierra Leone and portions of Guinea are well below normal. Beneficial rains fell in southern Liberia as indicated by the yellow hatched region. Crops and water supplies within the hazard region will be monitored. Forecasts indicate that little rain will fall during the next week.
Author: Kevin B Laws