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Soil moisture-Climate Feedbacks

Soil moisture-Climate Feedbacks. Erica Betts 04/10/2008. Influence of Land-Surface Evapotranspiration on the Earth’s Climate. J. Shukla and Y. Mintz Science , New Series, Vol. 215, No. 4539. Introduction. 2 experiments set at two extremes

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Soil moisture-Climate Feedbacks

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  1. Soil moisture-Climate Feedbacks Erica Betts 04/10/2008

  2. Influence of Land-Surface Evapotranspiration on the Earth’s Climate J. Shukla and Y. Mintz Science, New Series, Vol. 215, No. 4539

  3. Introduction • 2 experiments set at two extremes • Evapotranspiration is set equal to potential evapotranspiration (evapotranspiration with moist soil and complete vegetation cover) • No evaporation allowed to take place (surface devoid of any vegetation) • GLAS general circulation model ran for 60 days starting with June 15 atmospheric conditions

  4. Conclusions • For extratropical summer precipitation • If there is a large amount of moisture in soil in the spring, summer months can have low or high rainfall depending on circulation • If there is little moisture in the soil in spring, there will be little summer rainfall regardless of circulation • Modifications to Earth’s vegetation cover can influence climate, but this experiment still too coarse to give more specific response information

  5. Springtime Soil Moisture, Natural Climate Variability, and North American Drought as Simulated by the NCAR Community Climate Model 1 Robert J. Oglesby (1991) Journal of Climate, Vol. 4

  6. Introduction • Conclusions from 1989 paper • Reduction in summertime soil moisture over interior N.A. in perpetual July simulations leads to: • Increased surface temperatures, lower surface pressures, northward shift of jet stream • Reduced soil moisture in the summer can prolong/intensify existing drought conditions • Moisture advection from the Gulf of Mexico in determining what areas maintain lack of soil moisture and where this limitation is overcome • This 1991 paper seeks to extend these findings • What response will initially equilibrated climate have to instantaneously imposed soil moisture anomaly?

  7. Methods • Two sets of seasonal cycle simulations were run starting on May 1 and March 1 • May 1 runs for 153 • March 1 runs for 184 days • Initial soil moisture set at 0.01 (desert value) over 36°-49°N latitude • 10-year control run is used for comparison

  8. May Simulation

  9. Interpretation • Most of initial soil moisture anomaly is maintained and expands north and southward • Suggests a dry spring can induce hot, dry summertime conditions • Little amelioration of arid conditions due to moisture transport from the Gulf of Mexico

  10. March Simulation

  11. Interpretation • Soil moisture increases over the anomaly area by day 50. • Large area of soil moisture increase indicates that moisture advection from the Gulf of Mexico not an important factor • Snow cover also an important characteristic in the March vs. May simulations

  12. Control Simulation Typical moisture conditions Driest year in the 10 year run

  13. Control Simulation (Dry year)

  14. Conclusions • Control simulation shows some increase in soil moisture from May to July due to advection from Gulf of Mexico but May 1 and March 1 simulations do not • Assume that lack of importance from Gulf of Mexico shown in May 1 simulation due to lack of sufficient time • Spring soil moisture anomaly can impact summer drought conditions • Late winter/early spring soil moisture anomaly did not have significant impact beyond a couple of few weeks • Droughts of varying severity and spatial extent are part of the “normal” climate (occurred in one out of 8 years without induced soil anomaly)

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