Above average rainfall has been falling in many parts of the sub-Saharan African region since 2010, including countries like Angola, Namibia, Tanzania, Cameroon, Congo, and Madagascar.
The data comes from the Climate Prediction Center of the U.S. National Weather Service, which noted that large rainfalls have, in some places, exceeded the yearly average in a single day. In many parts of the continent, flooding persistent rains have flooded temporary rivers like the Kuiseb in Namibia and the Boteti in Botswana, both of which have recorded highs over the past year or so.
The map below depicts the rainfall for Namibia and South Africa on May 5, 2011, a day which saw more rain fall in the Namib Desert than normally falls in an entire year.
Ranging through shades of green and blue, rainfall estimates – compiled by NASA’s Multi-satellite Precipitation Analysis, based on data from the Tropical Rainfall Measuring Mission (TRMM) – range from 20 millimetres (0.8 inches) to greater than 70 millimetres (2.8 inches).
This compared to the average of less than 20 millimetres falling in the Namib Desert near the coast each year.
The main photo depicts what is likely a “shelf cloud” rolling over the Central Namib west coast, a cloud associated with a high precipitation supercell thunderstorm. According to NASA’s Earth Observatory, “the cloud spreads out at ground level due to a strong downdraft, which produces an advancing wedge of condensed water. Essentially, as large amounts of rain fall, the large and heavy rain droplets pull the air down with them. The curl at the bottom occurs because the down-drafting winds hit the Earth’s surface and spread out.”
During the most recent storm in southern regions, Francois Snyders of the Namibian Ministry of Environment and Tourism told The Cape Times that the Fish River area “got 50 millimeters of rain, which is more than the annual rainfall for the canyon.” Two dams, the Hardop and the Naute, were over capacity and had to open sluice gates.
Government officials and international aid and relief agencies have estimated that several hundred residents have been displaced or disrupted by flooding in Namibia, on top of the 62 who have died. Further concern is held for the ditches being caused by the heavy rains, which could have an impact on the roads, and the possibility of increased water- or mosquito-borne diseases due to stagnant water.
Source: NASA Earth Observatory