Variability, tendencies, and climate controls of terrestrial evapotranspiration and gross primary productivity in the recent decade over China

Accurately estimating regional water and vegetation carbon fixation and understanding their covariation mechanisms will benefit regional water resources and ecosystem management. The process-based vegetation interface processes model was employed to simulate the spatiotemporal variations of evapotranspiration (ET) and vegetation gross primary production (GPP) over the land mass of China, by integrating the 8-day Terra-MODIS leaf area index dataset from 2000 to 2013. It is found that there are remarkable spatial variations in annual ET and GPP across the country, top values being around 1,200mm for ET and 3,000gCm(-2) for GPP mostly occurred in the southern rainforests. Average annual ET and GPP are weakly increasing, in which about one third is significant. At annual scale, variability of ET follows precipitation variations, whereas variability of GPP follows variations of both precipitation and leaf area index. At monthly scale, variations of ET and GPP are more correlated with net radiation than precipitation. It is revealed that the climatic factors dominating water and carbon fluxes are different over the typical climate zones. The increasing GPP and water use efficiency are benefitting the regional vegetation recovery and carbon fixation, however, more water consumption may exaggerate the ecosystem vulnerability in water-limited zones.