中国西北地区植被干旱敏感性空间分异及其形成机制

The vegetation in the northwestern district of China acts as an eco-security shield, playing a prominent role in windbreak and sand fixation, soil and water conservation. However, its self-regulation ability and stability are weak, and it is vulnerable to drought. Vegetation sensitivity to drought characterizes the degree to which vegetation is susceptible to adverse effects of drought. It lacks the quantitative model of vegetation sensitivity to drought based on ecological processes at present. The research on spatial distribution characteristics of vegetation sensitivity to drought and its driving factors is limited. This issue is to be investigated for the vegetation in the northwestern district of China based on remote sensing and ground observations. The remotely sensed drought index and meteorological drought index are selected as the vegetation response and drought stress indicators. By analyzing the multi-time scale characteristics of meteorological drought index and its correlation with remotely sensed drought index, the spatiotemporal distribution characteristics of drought will be obtained. Also, quantitative models of vegetation sensitivity to drought will be developed by quantifying the time-scale of vegetation responses to drought, and the temporal and spatial correlations between vegetation vigor and drought stress. This study will identify the most susceptible vegetation types to drought and their spatial distribution, and highlight the formation mechanism of vegetation sensitivity to drought at landscape to regional scales, which may provide theoretical basis for desertification control and stability evaluation of dryland ecosystems under climate change.

中国西北地区植被是维护生态安全的屏障，在防风固沙、土壤保持和水源涵养方面发挥重要作用，但其自我调节能力和稳定性较弱，易受干旱胁迫。植被干旱敏感性表征植被易受干旱胁迫负面影响的程度，但目前尚缺乏基于生态过程的植被干旱敏感性量化模型，对于植被干旱敏感性的空间分异特征及其影响因素的研究明显不足。本项目拟以中国西北地区植被为研究对象，结合遥感监测与地面观测，以遥感干旱指数和气象干旱指数分别作为植被响应与干旱胁迫特征量，通过分析气象干旱指数的多时间尺度特性及其与遥感干旱指数的相关性，获取干旱的时空分布和演变规律，量化植被响应干旱胁迫的快慢程度、植被长势与干旱胁迫的时间与空间相关性，基于这些植被干旱敏感性表征变量，构建植被干旱敏感性量化模型，辨识正在遭受干旱胁迫的植被类型的空间分布，揭示景观和区域尺度植被干旱敏感性的形成机制，为气候变化背景下荒漠化防治和干旱生态系统稳定性评价提供理论依据。

中国西北地区植被是维护生态安全的屏障，在防风固沙、土壤保持和水源涵养方面发挥重要作用，但其自我调节能力和稳定性较弱，易受干旱胁迫。植被干旱敏感性表征植被易受干旱胁迫负面影响的程度，但目前尚缺乏基于生态过程的植被干旱敏感性量化模型，对于植被干旱敏感性空间分异特征及其影响因素的研究明显不足。本项目以遥感干旱指数和气象干旱指数分别作为植被响应与干旱胁迫特征量，开展以下三方面的研究：（1）评估常用干旱指数对不同干旱类型、季节性干旱和不同气候区干旱的监测能力，分析近二十年来干旱的时空变化规律，发现在干旱区和旱季，干旱指数对气象干旱和农业干旱的量化精度有待提高，对水文干旱和社会经济干旱的描述不适用。我国常年“南涝北旱”的格局似乎正在向“北涝南旱”转变，淮河流域、西南地区和青藏高原南部干旱化趋势加剧；（2）探究植被干旱敏感性的水平和垂直地带性分异规律，发现植被光合能力与干旱指数的相关性随干燥度增加呈高斯函数分布，相关性最高的地区分布在农牧交错带。植被光合能力响应干旱胁迫的时间随干燥度变化呈线性函数分布，但不同生态系统类型响应干旱胁迫的时间存在显著差异，且响应时间随干燥度变化的幅度差异明显。生态系统净初级生产力响应降水变化的敏感性随海拔升高先增加后降低，在灌丛草甸区达到最大。气候变化和过度放牧导致的草地灌丛化将增加山地生态系统对水分变化的敏感性；（3）以干旱影响植被生长的滞后效应和累积效应为基础，量化干旱胁迫影响下植被生长的响应时间和程度，构建基于干旱作用过程的新型植被光合干旱敏感性指数。干旱影响植被生长的滞后效应和累积效应表现十分普遍，且两种效应在多数情况下相互叠加。植被光合干旱敏感性指数准确识别中国北方生态干旱脆弱区，其中处于高、极高脆弱区的面积比例分别为23.7%和20.3%，主要分布在新疆、内蒙古、甘肃中西部、陕北、山西和和京津冀地区。上述研究成果可为气候变化背景下荒漠化防治和干旱生态系统稳定性评价提供理论依据。