Aridity and the Potential Physiological Response of C
3
Crops to Doubled Atmospheric Co
2
: A Simple Demonstration of the Sensitivity of the Canadian Prairies |
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| Authors: | R L Raddatz |
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| Institution: | (1) Meteorological Service of Canada, Prairie & Northern Region, Environment Canada, 123 Main Street, Winnipeg, MB, Canada, R3T 2N2 |
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| Abstract: | Since cultivated annual C3 field crops cover about50% of the land surface of the Canadian Prairie grassland eco-climatic zone, this vegetationinfluences the aridity of the climate during the growing season. The physiological response of these cropsto a doubling of the atmospheric concentration of CO2 may be a doubling of canopyresistance. If this physiological effect is not counteracted by interactive feedbacks, such as increasedleaf area, evapotranspiration rates could be reduced. To demonstrate the sensitivity of thearidity of the Prairie climate to this potential physiological effect, representative spring wheatgrowing-season soil moisture and Bowen ratio curves for a doubled canopy resistance(2 × CO2) scenario were compared with a control (1 × CO2) scenario.Lower evapotranspiration in the 2 × CO2 scenario: (1) Increased root-zone soilmoisture levels, and (2) weakened the atmospheric component of the hydrologic cycle by raisingBowen ratios, which reduces the convective available energy, and reduces the regionalcontribution to the atmospheric water vapour over the Prairies. A weakened hydrologic cycleimplies less rainfall, and possibly, lower soil moisture levels. Thus, the net impact of a doublingof the atmospheric concentration of CO2 on the aridity of the Canadian Prairies is uncertain.This simple sensitivity demonstration did not consider most of the potential feedback mechanisms,nor interactions of other processes. Nevertheless, the result illustrates that the physiologicaleffect should be explicitly included in climate change models for the Canadian Prairies. |
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| Keywords: | Aridity Climate change Convective rainfall Soil moisture |
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