Distribution of Deserts

My area of focus over the next couple of weeks will be away from desert hydrology and on to geomorphology, starting more specifically with desert dust. Desert dust is a critical component of the climate system at both a local and global scale.

As a prelude to a number of posts on the subject, it is worth highlighting where the various desert regions are found, and hence where dust may come from.

The US Geological Survey uses the following map to describe the locations of the worlds major desert regions.

It is highly apparent that the majority of the deserts are found at 30 degrees latitude north and south of the equator. This coincides with the falling limb of the Hadley Circulation and the subtropical high-pressure belt. Persistent thermodynamic stability results in a suppression of vertical motion and hence minimal precipitation. Compartmentalisation of anticyclonic cells breaks up subtropical subsidence explaining why hyperaridity is not prevalent across the latitudes (Ahrens, 2009). Georgia Southwestern State University provide useful diagrams that help to illustrate how global circulatory patterns are responsible for the distribution of deserts.

There are exceptions to this general rule. The great deserts of Central Asia, for example, can be attributed to the shear distance from the sea and hence pronounced sources of water. Greater seasonal changes in the desert environment may be associated with these continental interiors (Goudie, 2002). Furthermore, polar deserts are found largely because of the freezing temperatures and minimal precipitation.

There can be a number of regional factors that influence the precise formation and nature of particular deserts, but these will be examined later through specific case studies related to individual deserts.



References

Ahrens, C. D (2009) Essentials of Meteorology, Brooks/Cole: Belmont

Goudie, A.S. (2002) Great Warm Deserts of the World, Oxford: Oxford University Press.