大规模植被恢复对黄土高原生态水文过程的影响

Effects of Large-scale Vegetation Restoration on Eco-hydrological Processes Over the Loess Plateau,China

黄土高原退耕还林工程实施以来,大量坡耕地被转化为草地和林地,植被恢复效果显著,水土流失得到了有效控制.但是,由于植被剧烈变化,导致部分区域水资源供需矛盾进一步加剧.针对上述问题,本研究采用定位观测与模型模拟相结合的方法,在考虑植被恢复对地表水热过程影响的基础上,将双源蒸散发模型与遥感技术相结合实现尺度转化,构建考虑植被动态变化的区域尺度蒸散发模型,分析大规模植被恢复后黄土高原蒸散发、降水、径流量的变化趋势,明晰植被重建对生态水文过程的影响.结果表明,退耕还林(草)工程实施后,黄土高原全区降水以5.16mm·a-1的速率增加,而植被恢复最剧烈的16个子流域河川径流量呈不断下降趋势,平均降幅为-1.45mm·a-1.受植被恢复与重建的影响,研究区蒸散发以4.39mm·a-1的速率增加,植被恢复导致的冠层蒸腾上升是蒸散发增加的主要因素.基于上述结果,我们建议应当加强对黄土高原雨水资源潜力的利用,缓解植被剧烈变化导致的水资源消耗,并根据不同植被类型的蒸散耗水规律和区域土壤水分植被承载力,提出基于土壤水资源消耗补给平衡的植被恢复策略,以期为黄土高原生态恢复可持续发展和黄河流域水资源高效利用提供科学支撑.

Since the"Grain for Green"Project(Gf GP)was implemented on the Chinese Loess Plateau in 1999,many farmlands have been changed into grasslands and forests.The vegetation cover is significantly recovered from crops and bare soil so that the previous severe soil erosion is largely reduced.However,rapid change of vegetation type from crops to forests leads to less water supply and more water demand in some forest regions as the trees use more soil water than crop for evapotranspiration process.To quantitatively investigate effects of large-scale vegetation restoration on eco-hydrological processes as well as the tendency of the changes in precipitation,evapotranspiration,and streamflow,we use in-situ observations,PT-JPL evaporation model,and remotely-sensed vegetation and evaporation data to perform a series of simulations and analyses.The results show that during 2001 to 2015 period,precipitation increases at a rate of 5.16 mm·a-1,evapotranspiration increases at a rate of 4.39 mm·a-1,and streamflow in most basins,decreases at a mean rate of-1.45 mm·a-1.The increased canopy transpiration is the primary driving factor to the increase of total evapotranspiration.The findings suggest that it’s necessary to establish a set of scientific and practical strategy and policy by comprehensively considering the relationship between soil,vegetation,and water.Such a series of strategies and policies can potentially relieve water shortages caused by revegetation,and provide scientific guidance for sustainable development of vegetation restoration over the Loess Plateau and efficient management of water resources in the Yellow River basin.