塔里木河流域水分利用效率时空变化及其气候响应

Spatiotemporal dynamics of water use efficiency in the Tarim River Basin of western China and its response to climate change

摘要

【目的】全球气候变化下的旱区生态系统碳水循环地位日益凸显，生态系统水分利用效率作为衡量碳水耦合关键指标，其变化直接关系到生态系统功能的稳定性，因此明确旱区水分利用效率（WUE）的时空格局演变及其气候驱动因素是准确预测未来碳水循环对气候变化响应的重要前提。【方法】本研究以生态系统水分利用效率为对象，基于谷歌地球引擎平台调取 2001—2020 年 MODIS 遥感长时序数据，通过总初级生产力与蒸散发比值法计算并构建塔里木河流域 WUE 数据集；在此基础上，运用趋势分析和偏相关分析等方法，系统探究了 2001—2020 年塔里木河流域典型生态系统类型（农田、森林、草地）WUE 时空变化及其对气候因子的响应。【结果】（1）全流域及各生态系统年 WUE 均呈显著下降趋势。相对贡献率分析表明，ET 增长负向作用（59.12%）高于 GPP 增加的正向抵消作用（40.88%），是 WUE 下降的主导因素；（2）年 WUE 的时序变化及年际波动（去趋势后的时序变化）均与温度呈正相关、与降水呈负相关，其中长期趋势主要受降水调控，而年际波动则主要受温度驱动；（3）农田和森林 WUE 同样表现出与温度呈正相关、与降水呈负相关的特征，且农田 WUE 年际波动受温度调控明显；（4）月 WUE 对气候因子响应存在滞后性，滞后温度和降水分别为（2.37 ± 1.05）个月和（1.08 ± 1.25）个月，且农田对降水的滞后期显著短于森林，而对温度的响应滞后则显著长于森林。【结论】塔里木河流域 WUE 呈显著下降趋势，未来升温和降水增加可能通过加速蒸散发进一步抑制旱区 WUE，这意味着维持碳汇功能将面临更严峻的水资源压力，流域水资源配置与生态管理应考虑 WUE 气候响应的时间尺度差异及时滞特征。

Abstract

[Objective] Under global climate change, the role of dryland ecosystems in the carbon-water cycle has become increasingly prominent. As a key indicator for measuring carbon-water coupling, changes in ecosystem water use efficiency (WUE) directly affect the stability of ecosystem functions. Therefore, clarifying the spatiotemporal pattern evolution of WUE in drylands and its climatic drivers is an important prerequisite for accurately predicting the response of the future carbon-water cycle to climate change. [Method] This study took ecosystem water use efficiency as the research object. Based on the Google Earth Engine (GEE) platform, long-term MODIS remote sensing data from 2001 to 2020 were retrieved, and a WUE dataset for the Tarim River Basin was calculated and constructed using the ratio method of gross primary productivity (GPP) to evapotranspiration (ET). On this basis, methods such as trend analysis and partial correlation analysis were used to systematically investigate the spatiotemporal changes in WUE and its responses to climatic factors for typical ecosystem types (cropland, forest, and grassland) in the Tarim River Basin from 2001 to 2020. [Result] (1) Annual WUE showed a significant decreasing trend at both the basin and ecosystem scales. Relative contribution analysis indicated that the WUE decline was dominated by the negative impact of ET increase (59.12%), which offset the positive contribution of GPP growth (40.88%). (2) Both temporal variation and interannual variability of WUE were positively correlated with temperature and negatively correlated with precipitation. Specifically, long-term trends were mainly regulated by precipitation, while interannual variability was primarily driven by temperature. (3) Cropland and forest WUE also exhibited positive correlations with temperature and negative correlations with precipitation, with the interannual variability of cropland WUE being significantly regulated by temperature. (4) Monthly WUE showed a significant time-lag response to climatic factors, with lag times of (2.37 ± 1.05) months for temperature and (1.08 ± 1.25) months for precipitation. Notably, the lag time of cropland response to precipitation was significantly shorter than that of forests, whereas its response lag to temperature was significantly longer. [Conclusion] WUE in the Tarim River Basin showed a significant declining trend. Future warming and increasing precipitation may further suppress WUE in this arid region by accelerating evapotranspiration, implying greater water resource pressure for maintaining carbon sink functions. Therefore, water allocation and ecological management in the basin should account for the time-scale differences and lagged responses of WUE to climatic factors.

关键词

水分利用效率（WUE） / 气候变化 / 时滞效应 / 碳水循环 / 生产力

Key words

water use efficiency (WUE) / climate change / time-lag effect / carbon and water cycles / productivity

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基金资助

第三次新疆综合科学考察项目(2022xjkk0201)

国家重点研发计划课题(2023YFF0805604)

中央高校基本科研业务费专项资金项目(PTYX202526、PTYX202530、PTYX202533)