黄河流域植被格局变化对水分利用效率的影响

Characteristics of water use efficiency during the changing process of vegetation in the Yellow River Basin

黄河流域横跨3个气候带,是全球人类活动最为强烈的地区之一,特殊的地理位置和复杂的下垫面导致其碳-水循环过程较为复杂。研究黄河流域碳水循环不仅是区域水资源利用的基础,也是实现气候变化条件下双碳目标的关键。水分利用效率(WUE)作为表征碳水过程的重要指标,可用于反映生态系统碳水耦合规律及其相互作用关系。基于此,利用全球陆表特征参量数据(GLASS)的净初级生产力(NPP)和蒸散(ET)产品以及中国逐年土地利用与覆盖数据集(CLUD-A),分析了黄河流域植被格局变化背景下WUE在1990—2018年的时空变化特征及其驱动力。结果表明:(1)黄河流域全域WUE在29 a的均值处在0.18—1.53 g C/kg H_(2)O之间,存在明显的空间异质性,上游地区WUE明显高于中下游地区,分别在0.66—0.92 g C/kg H_(2)O和0.43—0.62 g C/kg H_(2)O之间波动,二者均存在波动上升态势。(2)黄河流域全域WUE在以2000年为中间点的10 a的增速达到近29 a的峰值,流域植被格局变化所带来的流域内NPP与ET变化速率的异步性主导了WUE变化的空间异质性,其中81.10%的区域中WUE所呈现的增加趋势是由NPP增速高于ET增速所导致。(3)黄河流域全域WUE在未来会继续保持增加态势,且上游WUE增加的持续性强于中下游地区。

The Yellow River Basin spans three climatic zones and is one of the regions of the most intense human activities in the world.The carbon-water cycle is complicated due to its special geographical location and the underlying surface.The study of the carbon-water cycles in the Yellow River Basin is not only the basis of regional water resource utilization but also the key to achieve dual carbon targets in the context of climate change.However,there are few reports about the carbon-water cycle at the whole basin scale.Water use efficiency(WUE),as an important indicator of carbon and water processes,can reflect the coupling law of carbon and water and their interaction in an ecosystem.Based on Net Primary Productivity(NPP)and Evapotranspiration(ET)data from GLASS and China's annual land-use/cover datasets,the temporal and spatial variation characteristics of WUE in the Yellow River Basin from 1990 to 2018 were analyzed,and the relationship between WUE,NPP and ET was discussed.The results are as follows:(1)the mean value of WUE in the Yellow River Basin was between 0.18 and 1.53 g C/kg H_(2)O in 29 years.There was obviously spatial heterogeneity.The WUE in the upper reaches of the Yellow River Basin fluctuated in 0.66-0.92 g C/kg H_(2)O and 0.43-0.62 g C/kg H_(2)O in the middle and lower reaches,and both of them had a rising trend of fluctuation.(2)In the Yellow River Basin,the growth rate of WUE reached a peak during 1995-2014,which is the decade with the year 2000 as the midpoint.The spatial heterogeneity of WUE was generated by the desynchrony of NPP and ET changes.Over 81.10%of the Yellow River Basin showed an increasing trend of WUE because the growth rate of NPP was higher than that of ET.(3)WUE in both the upper,middle and lower reaches will continue to grow in the future.In addition,the increase of WUE in the upper reaches is more persistent than that in the middle and lower reaches.