February 28, 2007
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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999
FROM VOLUME 12, NUMBER 3, MARCH 1999
Impacts of Land Degradation on Historical Temperature Records from
the Sonoran Desert, R. C. Balling, Jr., et al.,Climatic Change
40, 669-681 (1998).
Overgrazing has resulted in land degradation in northern Sonora in
Mexico. Temperature and precipitation records for that area were compared
with similar records for southern Arizona, where the land-use effects are
not as extreme, after correcting for the effects of latitude and altitude.
Sonoran locations warm faster, attain warmer temperatures, and exhibit
greater diurnal temperature swings during the summer.
Is Potential Evapotranspiration and Its Relationship with Actual
Evapotranspiration Sensitive to Elevated Atmospheric CO, Levels? J.
G. Lockwood,Climatic Change 40, 193-212 (1999).
Elevated levels of CO2 suppress transpiration per unit leaf
area. However, such suppression in grasses and other low vegetation is
minimal, and other components of the potential evapotranspiration (the
maximum amount of water that could be transpired by a homogeneous stand of
vegetation), such as interception loss (the precipitation that falls on
and evaporates from the canopy), would be unaffected by increases in
atmospheric CO2. Thus, suppression of potential
evapotranspiration would be small, but changes in evapotranspiration by
tall, slow-growing vegetation could be large. Therefore, water-balance
calculations will have to take this effect into account, especially in dry
climates, where interception loss is minimal.
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