Tradeoff between carbon sequestration and water resource in semiarid Loess Plateau

Background/Question/Methods

Forests are  known to have a large capacity of  carbon sequestration, and reforestation/afforestation has been recognized  as a potential strategy for the mitigation of global warming by reducing CO₂ through the photosynthesis processes. However, due to limited water resources  in the semiarid Loess Plateau of China, forest management practices toward carbon sequestration  is facing many challengs. Scientific understanding of carbon sequestration and water relationship is of paramount importance in the semiarid area. We examined regional net primary production (NPP) and water use efficiency (WUE)  (NPP/ET, evapotransporation ) using remote sensing data over 1999-2007 period representing  before and after the a massive afforestation program was implemented. We also examined  the tradeoffs between carbon sequestration and water resources with an monthly scale ecosystem model (WASSI-CB).

Results/Conclusions

Both NPP and water use efficiency of the Loess Plateau increased during 1999-2007. Afforestation had significant positive impact on NPP and WUE (P<0.0001). Annual precipitation was the key  factor affecting NPP and WUE (P<0.0001, R2=0.36). Ecosystems in regions with annual precipitation of  450-550 mm, experienced more prominent  increase in  NPP and WUE (P<0.01). As a whole, each unit increase in NPP (1 g C m-2) required  about an increase of water use by 0.48 mm waterion.