Invited by Dr. Paul Levine, Yue has given a presentation entitled “More forest, more drought?” in the group meeting of terrestrial hydrology in Jet Propulsion Laboratory (JPL) of California Institute of Technology.
In this presentation, Yue has given an introduction to his Ph.D. work on systematically assessing the hydrological feedback from the vegetation dynamics (including afforestation and vegetation greening) in China from 1982-2011.
Forest impacts on hydrological variables such as runoff and soil moisture are a classic topic in hydrological science. Previous studies using the paired catchment comparison method show that forest increases reduce the surface runoff and cause potential drought due to the enhancement of surface evapotranspiration (ET) (Brown et al. 2005; Jackson et al. 2005).
Yue has highlighted his recent paper “Divergent hydrological response to large-scale afforestation and vegetation greening in China“, in which he has applied a land-atmosphere coupled climate model to allow rainfall feedback from the vegetation dynamics. The rainfall feedback cannot be considered in the paired catchment comparison due to the plant impacts on large-scale circulation beyond the scope of previous studies. By allowing the rainfall feedback from vegetation, this paper has found the hydrological response to past afforestation and vegetation greening in China is divergent.
In North China and Southeast China, the rainfall increase by forest (not statistically significant) could easily cancel out the forest caused an increase in ET, with soil moisture not necessarily becoming drier. By contrast, Northeast China and Southwest China experience drying due to rainfall change very limited.
In the discussion after the presentation, colleagues from JPL and Yue have discussed a series of scientific challenges on the forest-hydrology relationship. These include: How to robustly isolate the forest feedback signal from the observations; Afforestation is different from reforestation, the land-use history could be important for local carbon sequestration capability but not for the ET, albedo change in biogeophysical impacts; Current vegetation model still use the concept of plant functional type (PFT), forest species effects on hydrological variables are still unknow.