Quantifying the effect of vegetation change on the regional water balance within the Budyko framework

The Budyko framework is widely used to investigate the impacts of climate and landscape changes on regional hydrology, but quantifying the effect of vegetation change is still a challenge due to the lack of an explicit expression of vegetation in Budyko equations. This study establishes a relationship between the change in the landscape parameter in a Budyko equation and vegetation change (represented by fPAR, the fraction of Photosynthetically Active Radiation absorbed by vegetation) for catchments in China, where, due to large-scale soil and water conservation projects implemented by the Chinese government, vegetation and regional hydrology have changed substantially over the past 30 years. The ratio of landscape parameter change to the change in fPAR has a strong relationship with the aridity index, and thus, vegetation change can be converted into a change in the landscape parameter. Then, the fPAR elasticity of runoff is introduced and formulated under the Budyko framework. It provides a useful tool for the quantitative evaluation of the regional hydrological response to vegetation change, but the proposed relationship still needs to be evaluated in other catchments around the globe where large-scale afforestation or vegetation recovery has occurred.