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    气象干旱和土壤水分对云南省植被的协同影响

    Synergistic impacts of meteorological drought and soil moisture on the vegetation in Yunnan

    • 摘要: 全球变暖背景下植被受气象干旱和土壤水分(soil moisture,SM)协迫的影响存在较多的不确定性,探讨SM和气象干旱对植被的协同影响对于评估干旱风险和生态系统健康至关重要。该文基于标准化降水蒸散指数(standardized precipitation evapotranspiration index,SPEI)和叶面积指数(leaf area index,LAI),对2001—2020年LAI、气象干旱和SM特征进行分析,并通过可解释的机器学习(Shapley additive explanations,SHAP)分析云南省不同深度SM和不同时间尺度SPEI对LAI的贡献度。结果表明: ①2001—2020年,云南LAI整体以0.37/10 a的增长趋势呈波动上升,各层次SM呈较弱的下降趋势,其中SM_Layer4最为明显,在月、季、半年和年4个时间尺度平均干旱强度以(-1.1,-1.0居多,大部地区平均干旱历时小于3.5个月; ②LAI和SM随气象干旱加剧而减小,其中气象干旱对浅层SM的影响最为明显, 重旱和特旱对LAI的影响更为强烈,中旱及以下级别的气象干旱对LAI的影响差异较小; ③4个时间尺度SPEI对LAI的影响均明显小于SM,湿润区深层SM对LAI的贡献高达74.3%~77.7%, 半湿润区和半干旱区浅层SM对LAI的贡献则高于深层SM。研究结果可为云南省生态系统可持续发展路线规划提供科学参考。

       

      Abstract: Under global warming, there remains considerable uncertainty regarding the impacts of meteorological and soil drought on vegetation. Exploring the synergistic impacts of soil moisture (SM) and meteorological drought holds significant importance for assessing drought risk and ecosystem health. Therefore, based on the standardized precipitation evapotranspiration index (SPEI) and leaf area index (LAI), this study analyzed the LAI, meteorological drought, and SM in Yunnan Province from 2001 to 2020. Then, it further investigated the contributions of SM at different depths and SPEI at varying temporal scales to LAI using interpretable machine learning methods, specifically SHapley Additive exPlanations (SHAP). The results indicate that from 2001 to 2020, the LAI in Yunnan exhibited a fluctuating upward trend with an overall growth rate of 0.37 m2 per decade. The SM at varying depths showed a weak decreasing trend, with the most pronounced decrease observed in SM_Layer4. The SPEI values predominantly ranged from -1.1 to -1.0 across the four time scales, with an average drought duration below 3.5 months in most areas. Moreover, both LAI and SM decreased with the intensification of meteorological drought, with the most pronounced reduction in SM occurring in shallow layers. Notably, severe and extreme meteorological droughts exerted stronger influences on LAI, while moderate and lower drought levels had impacts on LAI with minimal differentiation. Compared to SM, the SPEI across the four time scales had subordinate impacts on LAI. Specifically, in humid areas, deep SM exhibited a contribution to LAI reaching up to 74.3%~77.7%, while in semi-humid and semi-arid areas, shallow SM contributed more to LAI than deep SM. The results of this study provide a scientific reference for planning sustainable development pathways of ecosystems in Yunnan Province.

       

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