Assessment on spatiotemporal variations for minimum water consumption of vegetation in China based on constraint line method

Driven by climate change and artificial vegetation restoration, the actual vegetation water consumption (evapotranspiration) changes dramatically, in some relatively arid areas, the contradiction between growing vegetation water demand and limited terrestrial water resources becomes more prominent in recent years. For this reason, in actual ecological restoration or adjustment projects, clarifying the maximum vegetation coverage aiming at water balance is critical to maintain normal vegetation growth and sustainable use of water resources, and quantifying the minimum water consumption of vegetation (WCVmin) is a vital path to calculate this index. Currently, how to quantify WCVmin and identify its spatiotemporal variations remains unclear. Here we put forward an approach of quantifying WCVmin by using constraint line method and water balance principle, and we calculated the WCVmin of forest, shrubland and grassland and its spatiotemporal changes across China in 1990 and 2018, respectively. The results indicate: (1) our proposed method was proved to have robust spatiotemporal applicability; (2) compared with 1990, the average WCVmin rose by 7.46% in 2018, and the area that WCVmin enhanced accounts for 59.25%, in temperate continental and alpine climate zone, this proportion reached 81.76%; (3) meanwhile, the maximum plantable area of vegetation identified based on water balance (precipitation equals to WCVmin) reduced by 3.77%, which means it is increasingly difficult to implement sustainable vegetation restoration projects in relatively arid regions across China. This study is not only conducive to identify the regions where sustainable revegetation can be implemented under the constraint of water balance, but it also contributes to illustrate the evolution of the trade-off between vegetation water consumption and terrestrial water availability under changing circumstances.