Africa: Drought and floods hazards assessment: 25 Sep 2003

Report
from US Agency for International Development
Published on 25 Sep 2003


Update of the ITCZ Position

In general, the Intertropical Convergence Zone over Africa has continued its southerly migration and is located near 17.0 degrees north latitude, which is about 0.4 degrees north of normal for the current period. This is around 0.7 degrees south from the previous period and about 3.0 degrees south of its maximum northward seasonal position. The rainfall accumulations in the western Sahel correspond to the slightly southward anomaly in the ITCZ as compared to the 1988-2002 climatological mean. The heaviest showers continue in southern Senegal, northern portions of Guinea, and Guinea Bissau as the convergence zone continues its southward migration. Rains also increased along the Gulf of Guinea region, mainly over Liberia and southern Cote d'Ivoire and Ghana. The region from 10 degrees east to 10 degrees west longitude (western ITCZ region) is very close to the climatological mean, while the convergence zone from 20 degrees to 35 degrees east (eastern ITCZ region) remained similar to the last 10-day period, which was slightly north of the mean.

With respect to the weather over Africa, as noted above, heavy rainfall continued over portions of southern Senegal, northern portions of Guinea, and Guinea Bissau during the previous week where rainfall amounts exceeding 100 mm with some local heavier amounts. As the ITCZ continues to move southward, rainfall amounts have increased over Liberia and southern Cote d'Ivoire and Ghana as the second growing season is set to begin. Daily rain showers continued over northern Ghana, Togo, and Benin. Many of these areas have reported flooding over the past several weeks. Heavy rain also continued along the Cameroon-Nigerian border where a flooding region was present during the past hazard period. Elsewhere, isolated storms brought rainfall totals that were greater than 75 mm along the Ethiopia-Sudan border and in western Eritrea. Isolated portions of southern Sudan and Chad also had heavier amounts as tropical waves continue to move across the central portions of the continent. In southern Africa, rainfall amounts were around 25 mm over most of Angola, Namibia, South Africa, and Lesotho. Local amounts were heaviest in central Angola where rainfall was estimated over 100 mm.

NOAA/CPC USGS



WEEKLY AFRICAN WEATHER HAZARDS ASSESSMENT STATEMENT
SEPTEMBER 24, 2003 DISCUSSION:

1) Recent very heavy rains have resulted in elevated antecedent moisture levels across southeastern Senegal, the Northern Region of Ghana, southern Cameroon, southeastern Nigeria, as well as adjacent parts of neighboring countries. It is likely that many of these locations will receive significant amounts of additional rainfall during the period. As a result, the potential for flooding exists. In mountainous areas, the potential for landslides also exists.

2) Much below normal rainfall three years in a row has resulted in long term drought across southern Sanaag and northern Sool regions in Somalia. Long term drought has degraded pastures across the area. Some relief is possible during period with scattered showers expected. The area's minor rainy season occurs during mid and late September. More substantial rains typically occur during the major wet season in May and June.

3) Seasonal rainfall across the southernmost portions of the Ethiopian highlands has been below normal and erratic. This may negatively impact local agriculture and water supplies. Because of the high amount of variability and complexity of terrain across this region, some locations may be experiencing good seasonal rains while others may not. As a result, not all areas included in the shaded region are affected. Likewise, it is possible that some locations near, but not within, the shaded region are being affected by dryness and erratic seasonal rains.

4) Recent rains have resulted in rather high amounts of moisture in parts of eastern Sudan and adjacent Ethiopia. Scattered thunderstorms during the week may be locally heavy, mainly in northern parts of the hazard area. As a result, the potential for flooding exists. Widespread flooding is not expected.

5) Above normal rains over the past 6 weeks has resulted in some flooding problems across parts of southwestern Kenya. Seasonal showers, some of which may be locally heavy, are expected across southwestern Kenya. As a result, the potential for flooding exists across southwestern Kenya and adjacent parts of Uganda. Widespread flooding is not expected.

6) Rainfall totals for the 2002-03 rainy season were between 40 and 65% of normal across northeastern South Africa, southern Mozambique, and much of Swaziland. Seasonal rainfall deficits range from 150 to 400 mm across the region. This has resulted in a hydrologic drought across the region, reducing water supplies for wells, reservoirs and watersheds. Recent showers across northeastern South Africa have increased top soil moisture, but have done little to ease the drought. Except for a few showers across the southern and western parts of the area, conditions will be dry throughout the period.

7) The mini dry season set in about a month early across southern Cote D'ivoire and southwestern Ghana. Second season rains have also been slow to start, resulting in rainfall deficits during the month of September. This has raised concerns about second season crops in the area. However, rainfall is expected to increase in frequency and intensity during the period, indicating a possible start to the second wet season.

8) Wet weather during the past week has elevated moisture levels across parts of northwestern Africa. An active weather pattern will bring more rainfall, some of which may be locally heavy, to northeastern Algeria and northern Tunisia during the period. As a result, the potential for localized flooding and landslides exists.

AUTHOR: Chester V. Schmitt