Thursday, August 5, 2010: 9:00 AM
403-405, David L Lawrence Convention Center
Background/Question/Methods Warmer atmospheric temperatures will affect ecosystem functioning directly through changes in metabolic rate and tissue damage of organisms. Indirectly, increased temperatures can also affect ecosystem water balance with increased evapotranspiration (from bare-soil evaporation and transpiration) that reduces soil water availability. Although the amount of warming may be similar among ecosystems, it is likley that there is differential sensitivity of North American ecosystems to warming-induced soil drying.
There is a major gap in our understanding of ecosystem sensitivity to warming at the continental scale because experimental studies lack full geographical coverage. We ran an ecosystem model, SOILWAT for 52 sites across the U.S. encompassing a broad continental range of long-term water availability as well as a range of temperature and precipitation. We ran the model under historic conditions and 8 climate-change scenarios, 4 warming and 4 reduced precipitation scenarios. We calculated a Drought Equivalence to Warming (DEW) index for all sites, which we defined as the decrease in precipitation that must occur to achieve an equivalent reduction in soil water content caused by a warming of 1°C.
Results/Conclusions Our results show that there are significant differences among ecosystems in their response to the same degree of warming and that sensitivity is a function of the long-term water balance. Specifically, DEW or the degree to which warming-induced soil drying occurs, is a function of long-term water availability. A hump-shaped function depicted the relationship between DEW and Aridity Index (p <0.05 r2 =0.36 ) indicating that the indirect effect of warming is maximal in ecosystems where water demand and availability are close to a balance, and warming will alter it by increasing demand.We developed DEW maps for North America showing areas of maximum and minimum sensitivity to warming that can be used to guide future experiments to test our results.
There is a major gap in our understanding of ecosystem sensitivity to warming at the continental scale because experimental studies lack full geographical coverage. We ran an ecosystem model, SOILWAT for 52 sites across the U.S. encompassing a broad continental range of long-term water availability as well as a range of temperature and precipitation. We ran the model under historic conditions and 8 climate-change scenarios, 4 warming and 4 reduced precipitation scenarios. We calculated a Drought Equivalence to Warming (DEW) index for all sites, which we defined as the decrease in precipitation that must occur to achieve an equivalent reduction in soil water content caused by a warming of 1°C.
Results/Conclusions Our results show that there are significant differences among ecosystems in their response to the same degree of warming and that sensitivity is a function of the long-term water balance. Specifically, DEW or the degree to which warming-induced soil drying occurs, is a function of long-term water availability. A hump-shaped function depicted the relationship between DEW and Aridity Index (p <0.05 r2 =0.36 ) indicating that the indirect effect of warming is maximal in ecosystems where water demand and availability are close to a balance, and warming will alter it by increasing demand.We developed DEW maps for North America showing areas of maximum and minimum sensitivity to warming that can be used to guide future experiments to test our results.
