Aridity and Drought - not the same thing
Aridity is a dry climatic condition predominating in a region; drought refers to a period of time when conditions are drier than usual.
Namibia, as a constant, has an arid to semi-arid climate and is therefore not in a state of perpetual drought, however natural cycles of variability in rainfall do occur - generally in 10-year cycles.
While the wetter Caprivi region can receive as much as 500 mm of rain on average a year, the coast has less an 10 mm - yet can have humidity over 100% due to precipitating fog (pressure and saturation causing fog to ‘rain’). These conditions have resulted in some fascinating desert adaptations along the coast - see our blog on Namibia’s Fog Desert
The wind-driven cold, upwelling Benguela Current has a drying effect on Namibia’s climate, especially along the coastal belt.
Added to that, Namibia lies within the high-pressure zone of descending (hot and dry) air that encircles the earth (between 17 and 29 degrees south of the equator).
Average rainfall showing considerably higher rainfall in the east of the country.
The Namib Desert falls into the light blue zone that extends the entire length of Namibia's coast.
Having deposited its moisture load in the north and east of the continent, little atmospheric moisture remains to fall on the western side of the continent. It is thus the absence of moisture in the atmosphere, rather than lack of rain, which results in about 92% of Namibia being classified as semi arid to arid. When no rain fall for several years, then we can speak of drought....until then, the desert is a desert because of the absence of atmospheric moisture.
Lack of atmospheric moisture means few clouds (thus less rain) and because of less cloud cover, solar radiation is higher, meaning elevated ground temperatures and thus increased evaporation. The potential for evaporation in these conditions can be 5 times higher than precipitation (rainfall).
The measure of aridity is the difference between rainfall and potential evaporation (due to radiation)
The soaking effect of fog (image right)
One experience of the soaking effect of fog - most who have ridden on our westward orientated rides will have experienced this - is sufficient to understand how desert-adapted flora and fauna are able to take advantage of the hours when low fog predominates.
Once the sun is up, evaporation is extremely rapid….it is the early beetle that drinks the fog….
The fog-basking beetle, up early to take advantage of fog precipitation on its body.
The flora and fauna of the Namib Desert are a fascinating discovery for those who see these landscapes for the first time and wonder how anything can survive here....they not only survive, they thrive.
Welcome to our world...