The Kalahari Desert is considered a semi-arid savanna, with a clear wet and dry season. Despite the seasons, much variation in the hydrology of this location can be found when analyzing the different regions of the desert, specifically the outskirts, and the heart of the Kalahari. The groundwater recharge in the Kalahari Desert today is measured at about 5 mm a year towards the edges of this location, and as little as 1 mm a year in the central region of the desert.
http://www.photocircle.net/eu/photos/dennis-wehrmann/15361-Kalahari-Desert-Sunrise-Namibia |
The difference in groundwater recharge that is seen
throughout the different areas of the desert correlates to the amount of
rainfall measured at the edges of the Kalahari, compared to the center. Over
400 mm of annual rainfall has been recorded towards the outskirts of the
desert, with a much lower precipitation rate, less than 350mm, at the center.
Thus a pattern in the hydrology of the Kalahari Desert emerges,
with consistent high groundwater recharge near the edges, and significantly
lower recharge near the center.
Because of this pattern, we see landscapes closer to the
borders of the desert reflecting that of a high infiltration capacity
environment, with more vegetation, and a very dry, arid landscape of low
infiltration capacity towards the middle.
With less rainfall being absorbed by the earth in certain
parts of the desert, one can observe erosion in the form of rills and gullies,
as rainfall runs off quickly into streams.
Although some humans, like the San People, live near the
outskirts of the desert, due to the extreme conditions of the Kalahari, the
landscape is not very suitable for humans, as the annual rainfall in each
region struggles to support the vegetation and wildlife alone. An increase in
the groundwater table would provide more suitable conditions for human
accommodation, but such a thing would require an extreme and consistent annual
rainfall increase.
Interesting Video outlining where the Kalahari gets it's little moisture from. One way the groundwater table might increase in the future, providing more rainfall for the Kalahari, would be if the Maloti Mountains in Lesotho were to erode away.
https://www.youtube.com/watch?v=f_96xW6eF1Q
References:
http://www.hydrology.nl/images/docs/dutch/key/De_Vries_Groundwater_Recharge_Kalahari.pdf
https://www.britannica.com/place/Kalahari-Desert
https://ucdenver.instructure.com/courses/342696/files/3965142?module_item_id=898889
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