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Heavier-than-normal rainfall over the past month has brought flooding to parts of southern Africa. The hardest hit areas include Zimbabwe, Zambia, Malawi and Mozambique. All together up to 120,000 people have been displaced by the recent flooding along with 45 fatalities. The floods are also expected to have a severe impact on crops. December and January are part of the wet season in southern Africa primarily due to the southward seasonal migration of the Intertropical Convergence Zone (or ITCZ) during the Southern Hemisphere summer. In addition to the regular rainy season, during La Nina, which is currently on going, this area is expected to see enhanced rainfall. Another factor is a 30-to-60 day oscillation known as the Madden-Julian Oscillation (MJO). The MJO is a large, slow-moving area of enhanced tropical convective (i.e., thunderstorm) activity that propagates eastward from the Indian Ocean into the Pacific and can effect rainfall over Africa on sub-seasonal time scales.

The primary mission of the Tropical Rainfall Measuring Mission or TRMM satellite is to measure rainfall over the global Tropics. It was placed into service in November of 1997. From its low-earth orbit, TRMM has been measuring rainfall over the global Tropics using a combination of passive microwave and active radar sensors. It can be used to calibrate rainfall estimates from other satellites. The TRMM-based, near-real time Multi-satellite Precipitation Analysis (MPA) at the NASA Goddard Space Flight Center monitors rainfall over the global Tropics. Average daily MPA rainfall totals as well as rainfall anomalies (deviations from the average, which is based on a 9-year climatology) are shown here for the 31-day period 24 December 2007 to 25 January 2008 for southern Africa and the surrounding area. The highest rainfall totals (left panel) for the period (shown in red) are near 20 mm per day (~620 mm or 24 inches for the entire period) and are located over Malawi. Areas on the order of 15 mm/day (~18 inches for the period, shown in orange) cover parts of central Mozambique, Zambia and southeastern Angola. The highest anomalies (right panel) indicating wetter- than-normal conditions (shown in blue) follow a similar pattern. Nearly the entire region is experiencing wetter-than-normal conditions as indicated in green.

The Tropical Rainfall Measuring Mission (TRMM) is a joint mission between NASA and the Japan Aerospace Exploration Agency (JAXA).