资源环境科技发展态势分析平台

Climate model projections using offline aridity and/or drought indices predict substantial terrestrial drying over the twenty-first century(1-11). However, these same models also predict an increased runoff(12-15). This contradiction has been linked to an absence of vegetation responses to an elevated atmospheric CO2 concentration [CO2] in offline impact models(12,14,16,17). Here we report a close and consistent relationship between changes in surface resistance (r(s)) and [CO2] across 16 CMIP5 models. Attributing evapotranspiration changes under nonwater- limited conditions shows that an increase in evapotranspiration caused by a warming-induced vapour pressure deficit increase(18) is almost entirely offset by a decrease in evapotranspiration caused by increased r(s) driven by rising [CO2]. This indicates that climate models do not actually project increased vegetation water use under an elevated [CO2], which counters the perception that ` warming leads to drying' in many previous studies(1-11). Moreover, we show that the hydrologic information in CMIP5 models can be satisfactorily recovered using an offline hydrologic model that incorporates the [CO2] effect on r(s) in calculating potential evapotranspiration (E-P). This offers an effective, physically-based yet relatively simple way to account for the vegetation response to elevated [CO2] in offline impact models.