黄土高原退耕还林（草）以来植被水分利用效率的时空特征及预测

水分利用效率(WUE)是评估生态系统水碳循环的重要指标。基于PT-JPL模型的区域尺度实际蒸散发(ET)的模拟结果,结合黄土高原的总初级生产力(GPP),分析了退耕还林(草)工程实施后黄土高原水分利用效率WUE的时空变化趋势,结合CMIP6对未来3种情景下黄土高原的ET、GPP和WUE进行了预测。结果表明:2001—2015年,黄土高原植被显著增加,GPP和ET分别以每年3.59 g C·m^-2和4.39 mm的速率增加。WUE在72.68%的地区呈增加趋势,区域增长率为0.003 g C·mm-1·m-2·a-1。在2015—2100年的3种情景中,ET均呈增加趋势,而GPP和WUE在SSP126中变化不大,在SSP245、SSP370情景中显著增加,WUE随着GPP的增加而增加。WUE结合了水资源的"消耗"和"利用"来阐明退耕还林(草)工程的成效,植被恢复虽然增加了区域耗水量,但是显著改善了植被覆盖情况,有效地提高了植被的固碳能力和水分利用效率,整个黄土高原植被的抗旱能力在增强。未来需进一步分析不同树种的WUE,筛选出抗旱性更高的树种进行植被恢复工作。

Analysis of the spatial and temporal analysis and prediction of water use efficiency since the Grain for Green Projectin the Loess Plateau

Since the Grain for Green Project was launched in the Loess Plateau in 1999, the vegetation restoration effect has been significant. However, a high degree uncertainty in changes and predictions of regional water and carbon cycles caused by vegetation changes hinders the development of vegetation restoration assessment and prediction. Water use efficiency (WUE) is an important indicator for assessing the water-carbon cycle in ecosystems. Based on the simulation results of regional scale actual evapotranspiration (ET) by the PT-JPL model, combined with the GPP of the Loess Plateau, this paper analyzes the temporal and spatial trends of WUE on the Loess Plateau after the Grain for Green Project, and further uses CMIP6 to predict the WUE's of Loess Plateau under three scenarios. The results show that vegetation in the Loess Plateau increased significantly from 2001 to 2015, and that GPP and ET increased at rates of 3.59 g C·m^-2 and 4.39 mm per year, respectively. WUE increased in 72.68% of the regions with an average annual 0.003 g C·mm^-1·m^-2 increase. In the three scenarios from 2015 to 2100, ET showed an increasing trend while GPP and WUE didnot change much in SSP126 and increased significantly in SSP245 and 370 scenarios. WUE increased with the increase of GPP. WUE combines "consumption" and "use" of water resources to illustrate the effectiveness of the Project. Although the revegetation increases regional water consumption, it has significantly improved the vegetation cover, effectively enhanced the carbon sequestration capacity and water use efficiency of the vegetation, and increased the drought tolerance of the entire Loess Plateau vegetation. The WUE's of different tree species need to be further analyzed to screen out the tree species with higher drought resistance for vegetation restoration. The ecological construction and water conservation of the whole region is an eternal topic, and the healthy development of water-carbon cycle should be improved in current climate context in order to provide a better theoretical guarantee for the synergistic development of economic construction and ecological civilization of the Loess Plateau.