The nature of moisture at Gobabeb, in the central Namib Desert

摘要

This paper reviews the nature of moisture at Gobabeb, Namibia with emphasis on rainfall, and fog. It introduces the observational record produced by the Gobabeb Training and Research Centre and examines nature and cause of the rainfall record from October 1st 1962 to May 30th 2011. Over this period of 17749 days only 381 rainy days produced a total of 1213 mm of rain with an annual average of 25 mm. 2011 has been the wettest year on record also featuring the two most wettest days (March 12th and May the 6th). 1992 has been the driest year with no rain at all. Over the last 3 decades (1979-2009) the number of decadal rain days has decreased from 77 to 56 to 54 days, while total decadal rain amount has increased from 130 mm to 149 mm up to 300 mm. 193 Individual rain events between 1979 and 2009 were linked to synoptic conditions present in the region including the Zaire Air Boundary (ZAB), Tropical Temperate Troughs (TTT), the Angola Low, temperate cold fronts and cut-off lows (850 hgt geopotential height). Cluster analyses in the form of Self Organising Maps (SOMs), suggests that all synoptic states have the potential to produce rain but that the Angolan low dominates with an increase in TTT activity being evident Fog collection techniques have evolved through time and suggest a range of possible event types, including advected fog, coastal stratus cloud, high stratus cloud, radiation fog and fog drizzle. While each of these has their own meso- and micro-scale synoptic control and may even vary in their bulk and isotopic chemistry, they collectively make a significant moisture contribution to the flora and fauna of the Namib. Additional sources of moisture are gaining appreciation and include the widespread occurrence of hypersaline springs on the Namib gravel plains as well as micro-scale moisture including vapour in desert soils and regolith.