The Sahel region receives about 90% of its annual mean precipitation during the June-September period. This rainfall is closely related to the north-south movement of the Intertropical Convergence Zone (ITCZ), which begins its northward movement at the beginning of the Northern Hemisphere Spring and reaches its northernmost position (15°N) during August. During the 1995 rainy season much of the Sahel recorded near-normal rainfall totals (Fig. 67b), relative to the 1961-90 base period. This follows a significantly wetter-than-normal rainy season during 1994 and a near-normal year during 1993. This is the first time since the late 1970s that rainfall totals in the Sahel have been normal or above-normal for three consecutive years.
During 1995 above-normal rainfall was confined primarily to southwestern sections, where eastern Sierra Leone, northern Liberia, northern Cote D' Ivoire, and southern Guinea recorded more than 1000 mm of precipitation (Fig 67a) during the season (150-250 mm above normal). The most significant dryness stretched from southern Mauritania southeastward to Mali and Burkina Faso. Southern Senegal also experienced rainfall deficits with totals averaging between 600-700 mm during the season (Fig. 67a).
During June rainfall was generally near normal to above normal across the Sahel. However, rainfall deficits developed over Mauritania and Mali. Most countries in the Gulf of Guinea region also observed rainfall below 70% of normal during the month, except the coastal areas of Cote d'Ivoire, Benin, and Ghana, where stations reported above-normal rainfall. In July rainfall tended to be near normal or slightly below normal across the Sahel region. However, dry conditions prevailed in Mali and eastern Niger where rainfall was generally only 50 to 80 percent of normal. During August and September, rainfall was again near average across most of the Sahel. However, rainfall was particularly abundant (over 150% of normal) in a few locations, including southeastern Burkina Faso and parts of Benin and Senegal. Rainfall also improved significantly in southwestern Mali, Niger, and northern Burkina Faso during the period, where normal- to above-normal rainfall (95-170%) totals were recorded.
In southern Africa, the rainy season typically lasts from October to April, and reaches maximum strength between November and March. The region as a whole receives more than 75% (some parts more than 90%) of its mean annual precipitation during this seven-month period. Significant precipitation is rare throughout the region after mid-May. The year-to-year variability in rainfall over southern Africa shows a strong relationship to the ENSO cycle, with below-normal (above-normal) rainfall generally observed during Pacific warm (cold) episodes (Ropelewski and Halpert 1987, 1989).
Overall, rainfall totals during the 1994/95 rainy season were significantly below normal over large portions of southern Africa and Madagascar (Fig. 68). Rainfall deficits exceeding 150 mm (Fig. 68b) were observed throughout Namibia, southeastern Angola, much of Botswana, Zimbabwe, Mozambique, the southern two-thirds of Madagascar, and the northeastern section of South Africa. In many of these regions, the observed rainfall totals were generally 50-75% of normal, while in central Namibia the totals were only 25-50% of normal.
The rainy season in southern Africa was characterized by a slow onset, with rainfall deficits during November and December 1994 averaging 50 -200 mm across the subcontinent. These dry conditions improved slightly during January 1995, particularly over portions of Zimbabwe, northeastern South Africa, and parts of Botswana, where heavy rainfall (100-200 mm, over 150% of normal) was observed. However, during late January-February, abnormally dry conditions once again dominated southern Africa, with totals among the lowest 10% of climatological occurrences over southern Botswana, northern Zimbabwe, and central Mozambique. Dryness persisted through March over much of southern Africa, although heavy late-month rains provided much-needed moisture to many areas from Botswana and central Zimbabwe southward. However, below-normal rainfall continued through April in many regions, allowing moisture shortages to increase across much of southern Africa.
The onset of the 1995/96 rainy season in southern Africa brought a marked increase in rainfall totals for much of east-central South Africa and southwestern Namibia (Fig. 69 ). This increased rainfall helped to ease the long-term dryness that plagued the region throughout the first half of the 1990s. These changes are consistent with the onset of cold-episode conditions in the equatorial Pacific during the second half of the year (see section 3).
