黄土高原水分利用效率动态及其对干旱和地表温度的响应

Dynamics of water use efficiency and its response to drought and land surface temperature on the Loess Plateau

黄土高原是世界上土壤侵蚀最严重和中国增绿幅度最大的地区,研究该区水分利用效率(WUE)时空演变及其与干旱和地表温度(LST)之间的关系,已成为黄土高原最大植被容纳阈值选择的重要参考。基于Theil-Sen趋势法和一阶差分相对贡献量法分析了2001—2021年黄土高原不同季节WUE时空变化规律及干旱和LST对WUE变化的贡献情况。结果表明:(1)2001—2021年黄土高原春、秋季WUE平均值小于2.0 g C·m^(-2)·mm^(-1),夏季WUE平均值大于2.0 g C·m^(-2)·mm^(-1)。春、秋季耕地和林地区域WUE高于草地区域,夏季耕地区域WUE最低,林地区域次之,草地区域最高。(2)春、夏季WUE以稳定不变趋势为主,空间分布上均表现为“中部减少,西部和东部稳定不变”的特征,草地区域WUE下降速率>林地区域>耕地区域;秋季WUE以增加趋势为主,草地区域WUE上升速率>林地区域>耕地区域,空间分布上呈“西北增加,东南减少”的特征。(3)春、夏季LST对WUE变化为正贡献度,草地区域表现最为显著,秋季LST对草地和林地区域WUE为负贡献度,但对耕地区域WUE为正贡献度。春、秋季干旱对WUE变化为正贡献度,夏季为负贡献度。以上结果有助于认识气候变化和生态修复工程实施背景下黄土高原干旱和LST与水资源之间的关系。

The spatiotemporal variations of water use efficiency(WUE)and its relationship with drought and land surface temperature(LST)on the Loess Plateau are crucial for assessing the maximum vegetation carrying capacity in this region,known as the most severely eroded area globally and the largest greening area in China.This study employed Theil-Sen trend analysis and the first-order differencing relative contribution method to examine the spatiotemporal changes in WUE across different seasons on the Loess Plateau from 2001 to 2021 and to evaluate the contributions of drought and LST to these changes.The results reveal that:(1)The average WUE values in spring and autumn are below 2.0 g C·m^(−2)·mm^(−1),while in summer,the average WUE exceeds 2.0 g C·m^(−2)·mm^(−1).In spring and autumn,WUE is higher in cultivated land and forest areas compared to grassland areas,whereas in summer,WUE is lowest in cultivated land,followed by forest areas,and highest in grassland.(2)WUE remains stable in spring and summer,displaying a spatial distribution of“reduction in the central part,stability in the western and eastern parts.”The rate of decline in WUE is greater in grassland areas than in forest and cultivated land areas.In autumn,WUE shows an increasing trend,with a higher rate of increase observed in grassland areas than in forest and cultivated land areas,exhibiting a spatial pattern of“increase in the northwest,decrease in the southeast.”(3)In spring and summer,LST positively contributes to WUE changes,with the most significant impacts in grassland areas.In autumn,LST negatively affects WUE in grassland and forest areas but positively influences WUE in cultivated land areas.Drought positively contributes to WUE changes in spring and autumn,while it negatively affects WUE in summer.These findings enhance the understanding of the interactions between drought,LST,and water resources in the context of climate change and ecological restoration efforts on the Loess Plateau.