气候变化背景下全球陆地干湿变化研究综述

气候变化背景下，全球水循环加剧，出现了大气变干与植被变绿等陆地干湿变化趋势的解耦现象，旱区面积变化也存在争议。为回答上述问题，在梳理常见干湿指标变化趋势与驱动因素的基础上，根据指标变化方向对其进行归类，然后从机理角度解析影响不同指标趋势耦合或解耦的关键要素，并提出未来干湿变化研究展望。结果表明，气候变化背景下，饱和水汽压差、干燥度指数和土壤水分指标显著变干，植被绿度和生产力显著变湿(增加),降水、径流、陆地水储量和其他复合指标区域分异明显、但整体趋势不显著。二氧化碳浓度增加、气温升高和土地利用变化是导致不同指标趋势分异的重要因素，不同指标的趋势分异也解释了旱区面积评估在不同维度上的差异。未来研究中应开展干湿变化的综合评估，其综合性主要体现在以下四个方面：1)关注大气-生态-水文多维度评估；2)解析自然与人类双重压力下，不同维度要素间的关联、互馈过程，及其对系统干湿演变的促进、限制与调节作用；3)重视干湿演变程中的极端灾害事件和空间上以旱区为代表的气候变化敏感性区域；4)构建以脆弱性评估与适应性治理为核心的气候变化应对路径。

A review on the changes in wetting and drying over land under global climate change: trend, mechanism, and prospect

Under global climate change, the hydrological cycle intensifies and the wetting and drying over land is decoupled with atmospheric drying and vegetation greening. This triggers a hot debate on the changes in dryland area. To clarify that, we summarized trends of some widely-used aridity indicators, as well as their driving factors. We then classified these indicators into different groups based on their trends to explore the underlying mechanism of the coupled and decoupled trends among indicators. At last we provided prospect of future research on wetting and drying under climate change. Our results showed that among aridity indicators, vapor pressure deficit, aridity index, and soil moisture presented significant drying trends, vegetation greenness and productivity showed obvious wetting trends, while precipitation, runoff, terrestrial water storage and other composite indices showed great regional discrepancy but overall insignificant trends. Increasing CO₂ concentration, higher temperature, and human direct activities such as land use/cover change are the major factors causing differentiation among trends of the indicators, which accounts for the contradiction in dryland change (expanding or shrinking) in studies using various indicators. Therefore, a comprehensive assessment of changes in wetting and drying for terrestrial land is essential in the future by focusing on four priorities:1) multiple dimensions assessment including meteorology, ecology and hydrology; 2) interactive relationships (such as promotion, limitation and regulation) among multi-dimensional elements and their impact on wetting-drying changes under the double natural and human pressures; 3) the occurrence of extreme events (such as drought, flood, and heat wave) and the areas (such as semi-arid regions) sensitive to climate change in the process of wetting-drying; and 4) the possible solution to global climate change based on vulnerability assessment and adaptive governance.