COLA Report 3

The Effect on Climate of Doubling Deserts

P. A. Dirmeyer & J. Shukla

June 1994


Abstract

An atmospheric general circulation model with realistic land surface properties is used to investigate the climatic effect of doubling the extent of the earth's deserts. Control and anomaly integrations are performed for 10 years. In the anomaly case, deserts are expanded over North Africa, South Africa, Australia, south-central Asia, southwestern North America, and parts of South America.

In the anomaly case, the troposphere is cooler across most of the tropics and subtropics, including all areas where desertification occurs. Annual mean precipitation is reduced over North and South Africa, south-central Asia, and Australia. Precipitation over the eastern Sahel is reduced by over 60%, and droughts persist in all seasons over northern and southern Africa. Asia and Australia exhibit weaker monsoons, but there is little effect during winter. Precipitation increases over central Africa between the two desertified regions, over the ocean equatorward of Asia and Australia during those regions' monsoons, and over the desertified areas of western North America. Regions of increased rainfall occur over the ocean to the west of the desert regions of North and South America, Australia, and South Africa. Remote effects in the winter circulation include a pronounced trough over northern Europe, and increased geopotential heights over the southern oceans.


A Few Figures

Location of bare soil and steppe vegetation (shrubs with bare soil) in; (a) control case; (b) double desert case.

Mean anomalies due to desertification and statistical significance computed over the last 96 months of the model integrations for 500 hPa atmospheric temperature (degrees Kelvin, top) and precipitation rate (percent, bottom). Temperature contours are at ±0.3, -0.6, -0.9 and -1.2 K, precipitation contours are at ±10%, ±20%, ±40%, and -60%. Shading indicates statistical significance at the 95% confidence level.

Mean annual cycle of anomalies in precipitation (open circles) and evapotranspiration (filled circles) expressed as percentage deviation from the control case values. Values indicate area averages taken over the land areas where vegetation was degraded in each named region, with the exception of Monsoon Asia where the average was taken over all land between 75 E-110 E, and 10 N-38 N. Shading indicates anomalously low precipitation.


Complete copies of this report are available from:
Center for Ocean-Land-Atmosphere Studies
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last update: 18 October 1994
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