资源环境科技发展态势分析平台

The risks of flood and drought have been projected to increase in many regions due to global warming. Afforestation is considered an adaptation option because it reduces flood risks by decreasing total runoff and peak river discharge, but it also exacerbates drought risks by increasing evapotranspiration. In this study, both effects of afforestation were evaluated in comparison with changes caused by climate warming from the viewpoint of an adaptation measure, using a land surface model. The upper Chao Phraya River basin was taken as a case study. The present climate was set as a base condition and future climate conditions projected by the moderate (RCP4.5) and strong (RCP8.5) warming scenarios in the middle and late 21st century were used. The effects of afforestation were much smaller than the changes caused by warming even with the extreme forest area expansion and soil property changes. The effect of afforestation that reduced runoff was marked in the wet season, whereas the effect of afforestation that increased evapotranspiration was noticeable in the dry season leading to little increase in dry-season runoff. These results indicate that both the decrease in runoff that reduces flood risks in the wet season and the increase in evapotranspiration that exacerbates drought risks in the dry season should be taken into consideration when evaluating the hydrological effects of afforestation under global warming.