Africa: Drought and Floods Hazards Assessment: 14 Aug 2003

Report
from US Agency for International Development
Published on 14 Aug 2003


EL NIÑO/SOUTHERN OSCILLATION (ENSO) DIAGNOSTIC DISCUSSION

Current atmospheric and oceanic conditions in the tropical Pacific are near average and do not support the development of either La Niña or El Niño in the next few months. Equatorial sea-surface temperature anomalies greater than +0.5C persisted in the region west of the date line, while negative anomalies remained in the eastern Pacific, near the South American coast. During July very little net change was observed in the SST anomalies in the Niño regions. Several atmospheric indices have displayed considerable month-to-month variability since May 2003 and no consistent trend towards either La Niña or El Niño.

A majority of the statistical and coupled model forecasts indicate near neutral conditions (Niño 3.4 SST anomalies between -0.5C and +0.5C) for the remainder of 2003 and early 2004. This is consistent with current conditions and the lack of any consistent trends in the suite of oceanic and atmospheric indices.

This discussion is a consolidated effort of NOAA and its funded institutions.

Over Africa, drenching rains soaked a number of areas in the Sahel and Sahara region this past week, as the ITCZ advanced much farther northward than normal. Seven-day rainfall during August 5-11 reached 100 to 150 mm from extreme southern Mauritania into eastern and southern Senegal and Guinea-Bissau, including Gambia. A few locations picked up over 150 mm in southwestern Senegal and northern Guinea-Bissau. The bulk of the rain fell during one or two days during August 7-10. Up to 75 mm, with some higher totals, also hit areas in the Sahara that seldom see much rainfall, including northern Mali and northern Mauritania. Heavy rains exceeding 100 mm also struck parts of Burkina Faso, western Niger, northern Benin, northwestern Nigeria, central Sudan, and northern Ethiopia. Estimated weekly totals reached 75 mm in western Eritrea near the Ethiopian border. Dry weather continued from Liberia eastward across southern Cote d'Ivoire to southwestern Ghana. Long-term rainfall deficits persisted from Senegal's northern groundnut basin into southwestern Mauritania.




AFRICA WEATHER HAZARDS ASSESSMENT EXPLANATION VALID August 14-20, 2003

1) Recent 7-day rainfall totals in parts of southeastern Mauritania exceeded 100-150 mm and have helped to ease dryness in the region. While pockets of dryness remain, overall improvement in the area is noted. Latest ITCZ analyses and regional rainfall forecast models support additional relief in the area during the next week. Areas to the west into northwestern and central Senegal have remained dry for most of the past month and dryness continues in this region. The lack of precipitation may be affecting the groundnut basin in Senegal.

2) Recent weekly precipitation totals in southern Chad exceeded 75 mm and conditions remain favorable for areas of local flooding during the next week. Latest meteorological forecasts indicate areas of weekly rainfall greater than 150 from August 14-20 with widespread amounts exceeding 75 mm.

3) The heavy rainfall which occurred from July 26-30 near and east of Kassala in eastern Sudan has led to saturated soil conditions and bank-full rivers. Past 7-day rainfall totals from 50-150 mm in western Eritrea and northwestern Ethiopia are causing water runoff into downstream areas already inundated by high water. Additional locally heavy rainfall is forecast during the next week.

4) Beneficial rainfall has occurred over the central Ethiopian Highlands and adjacent pastures during the past four weeks, and this has helped to reduce dryness throughout the area. Farther to the south, however, rains continue to be lighter than normal, and southwestern Sudan is experiencing dryness as well. Latest regional forecast models show greater than 50 mm rainfall possible in these continued dry areas during the next three days. If this verifies, improvement will occur in the region.

5) A failure of rains in parts of northern Somalia has led to drought in the region. Little rainfall is expected in the near future as seasonal rainfall totals remain near 0-25% of normal.

6) Seasonal rainfall totals in parts of southern Somalia remain below normal after flood-producing rains in July fell over the area. Little rainfall is likely during the next few weeks as the season wraps up.

7) Weekly rainfall totals of 20-30 mm locally were seen from August 5-11 in parts of eastern South Africa affected by long-term drought. Although this has helped winter crops in the region, dryness continues in parts of southern Mozambique, southern Zimbabwe, eastern Botswana, and northeastern South Africa. Little precipitation is expected during the next seven days.

8) Up to 50 mm rainfall was reported in parts of Cape Town province in South Africa during the past week and lighter showers were seen throughout the hazard area. This trend is not expected to continue during the next week however, as dryness should prevail and winter moisture deficits remain.

9) The past few weeks has seen a dramatic increase in precipitation over previously dry areas of western Guinea and Sierra Leone, with recent weekly rainfall totals exceeding 100 mm throughout the region. Though seasonal rainfall deficits remain in these countries, the fact that the area usually receives such high totals lessens the impact of these lighter than normal rains. Locally heavy thunderstorms are again possible during the next week. Further to the east, into Liberia, Code d'Ivoire, and southwestern Guinea, seasonable dry conditions continue. Although rains are normally light during this time of year, previous rainfall deficits remain due to a very dry first rainy season. Forecast models are indicating a chance for moderate rains in parts of northern Cote d'Ivoire during the next week, but relief may be local and not widespread.

10) Parts of The Gambia, southern Senegal, and Guinea-Bissau received locally very heavy rains during the last week, with 7-day totals exceeding 200 mm in some locations. Additional rainfall was seen on August 12th as well, and forecasts show a good chance for more rains during the next week. Local periods of flooding may result from the heavier showers and thunderstorms as they move from east to west through the area.

11) Rainfall has been moderate to heavy over the past two weeks in the area in and surrounding western Niger, and this has led to local flooding problems in the region. Local reports of weekly accumulated precipitation during the past week exceeded 200 mm in some areas and additional rainfall is possible from August 14-20.

Timothy B Love