In southern Africa, the rainy season typically lasts from October to April and reaches maximum strength between November and March. Most locations receive more than 75% of their annual precipitation during this 7month period, with some parts in the northwest receiving more than 90% of their total annual rainfall. The year-to-year variability in rainfall over southern Africa shows a strong relationship to the ENSO cycle (Ropelewski and Halpert 1987, 1989), with below-normal rainfall generally observed during Pacific warm episodes (e.g., the 1994/95 rainy season) and above-normal rainfall generally observed during Pacific cold episodes (e.g., the 1995/96 rainy season).
Overall, very strong gradients in rainfall totals were observed across southern Africa during the 1995-96 rainy season, with the largest totals exceeding 1000 mm in the north and east, and the lowest totals of less than 100 mm in the southwest (Fig. 53a). Above-normal rainfall during the period covered the climatologically high precipitation areas such as northeastern South Africa, southern Mozambique, and much of central Madagascar (Fig. 53b ). For example, much of the northeastern sector recorded totals exceeding 200 mm above normal during the season, with isolated areas recording more than 400 mm above normal. Seasonal totals in these regions exceeded the 70th and 90th percentiles, respectively (Fig. 53c). This above-normal rainfall contrasts with the abnormally dry 1994/95 rainy season (Fig. 53d). Elsewhere during the 1995/96 wet season, below-normal totals were confined to climatologically low precipitation areas such as northern Namibia, eastern Angola, and western Zambia. These areas also received below-normal rainfall during 1994/95. Elsewhere, central South Africa, northern Botswana, southern Namibia, and northern Zimbabwe all received near-normal rainfall during the 1995/96 season.
The time series of percentiles of area-averaged monthly mean precipitation for the boxed region (15°-35oE, 18°-35oS) shown in Figs. 53a-c reveals a slow onset and an early end to the 1995/96 rainy season (Fig. 53d), with heavy rainfall recorded from late-November through February. In fact, the period December-February brought significantly above-normal rainfall to the region, with mean totals during December and January approaching the 90th percentile and totals during February approaching the 70th percentile.
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