GEOG 3103 Lecture 7: Drylands & wetlands
21 Mar 2017
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Xerothermic index: number of days biologically dry /year for an area ( varies between 0& 365) Water tavle & vegetation follows rhythm of rains. 25% of land surface outside of polar regions is desert- most in 30 n& s of equator. Direct sunshine-warm air absorbs moisture from warm ocean- rises, cools, rains in tropical belt now drier air flows n& s, falls back, absorbs more moisture, causing infrequent rain & arid regions. Topography: rain-shadow deserts: orographic effect dries air, causes high pressure zone on leeward side. Continental interiors: with distance from coats, air generally dries out, causing arid zones (talka makan desert in w. china) Cold ocean currents : cool currents flow along certain coasts , chilling sea air. Exposed sun temperatures: 82 c in air over bare rock & sand. Night - time radiation- extreme temperature drops & frost or dew. Many dryland areas are source regions for dry air masses.
