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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

JOURNAL ARTICLES...
LAND-COVER EFFECTS

Item #d99mar17

“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.

Item #d99mar18

“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.