Extreme rainfall in the Namib desert during late summer 2006 and influences of regional ocean variability



The desert country of Namibia (southwestern Africa) and adjoining areas received anomalously heavy rains in austral summer 2006. In particular, the hyper-arid southern Namib Desert experienced an extreme rainfall event in mid-April 2006 which led to the coastal station of Luderitz receiving 102 mm, or about six times its annual average rainfall. Based on extreme value theory, this event appears to have a return period of 145 years—the rainfall received at Luderitz during 16–23 April 2006 was about twice that of the annual rainfall recorded at this station in the previous wettest year (1956).

It is argued that this event occurred as a result of the unusual interaction of an anomalously westward-located tropical-extratropical cloudband, and an anomalously northward-located cut-off low. In turn, the location and behaviour of these synoptic features may have been aided by regional ocean conditions, a strong warm event in the tropical southeast Atlantic and a positive dipole-like sea surface temperature event in the south Indian Ocean, together with La Niña conditions. It is argued that the combination of these regional ocean patterns with the La Niña event led to the very wet conditions over Namibia and neighbouring countries during austral summer 2005–2006. Copyright © 2007 Royal Meteorological Society