半干旱地区退耕还林还草工程在增加植被覆盖的同时，也使流域产流和土壤含水量下降。如何权衡两者的关系？中国科学院生态环境研究中心傅伯杰研究组与北京大学等单位的合作研究发现，目前黄土高原植被恢复已接近该地区水资源植被承载力的阈值。成果8月8日在线发表于《自然—气候变化》。

“2000年以来我国实施的大规模退耕还林还草工程是世界上规模最大的植被恢复工程，其中又以黄土高原植被覆盖增加和各项生态系统服务功能的提高最为显著，但同时观测也发现该地区流域产流和土壤含水量显著下降。”中科院院士傅伯杰接受《中国科学报》记者采访时说。

傅伯杰介绍，他们通过耦合地面观测、遥感和生态系统模型等多种手段，量化分析了黄土高原地区植被恢复的固碳、径流、蒸散发等生态效应，构建了自然—社会—经济水资源可持续利用耦合框架，提出了当前和未来气候变化情景下黄土高原退耕还林的阈值。

“目前黄土高原植被恢复已接近该地区水资源植被承载力的阈值，在未来气候变化条件下，该承载力阈值在383~528克碳/平方米·年间浮动。”傅伯杰表示，这对指导黄土高原退耕还林还草工程的实施具有重要意义。他建议，黄土高原植被恢复应综合考虑区域的产水、耗水和用水的综合需求。（来源：中国科学报 陆琦）

Revegetation in China’s Loess Plateau is approaching sustainable water resource limits

Abstract  Revegetation of degraded ecosystems provides opportunities for carbon sequestration and bioenergy production. However, vegetation expansion in water-limited areas creates potentially conflicting demands for water between the ecosystem and humans. Current understanding of these competing demands is still limited. Here, we study the semi-arid Loess Plateau in China, where the ‘Grain to Green’ large-scale revegetation programme has been in operation since 1999. As expected, we found that the new planting has caused both net primary productivity (NPP) and evapotranspiration (ET) to increase. Also the increase of ET has induced a significant (p < 0.001) decrease in the ratio of river runoff to annual precipitation across hydrological catchments. From currently revegetated areas and human water demand, we estimate a threshold of NPP of 400 ± 5 g C m⁻²yr⁻¹ above which the population will suffer water shortages. NPP in this region is found to be already close to this limit. The threshold of NPP could change by −36% in the worst case of climate drying and high human withdrawals, to +43% in the best case. Our results develop a new conceptual framework to determine the critical carbon sequestration that is sustainable in terms of both ecological and socio-economic resource demands in a coupled anthropogenic–biological system.

原文链接：http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate3092.html