NATS 1750 Lecture 14: Deserts
12 Apr 2016
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Document Summary
A dry climate is one where yearly precipitation is not as great as the potential for evaporation. Dry regions cover 30 percent of earth"s land surface. Two water-deficient climatic types are commonly recognized. Desert (arid) regions are more dry than steppe (semiarid) regions. So although we think of a desert as a place with little or no rainfall, this is only part of the situation. In many cases, there are areas of low rainfall that are not what we would consider desert because the evaporation rate is very low. On earth a major cause of arid lands in the subtropical highs. Here the prevailing wind and atmospheric circulation cause the air to be warm and dry, reducing rainfall and increasing evaporation rates. (figure 21. 3) Another major cause of arid areas is the rainshadows created by mountain ranges. The wind as it rises up the windward side of the mountains, cools and drops much of its moisture as rain.
