黄河流域植被水分利用效率对干旱的时空累积响应

Spatiotemporal accumulation response of vegetation water use efficiency to drought in the Yellow River Basin

利用植被总初级生产力和蒸散发数据,结合标准化降水蒸散发指数(SPEI)数据,分析了1982—2018年黄河流域植被水分利用效率的变化特征,量化了干旱对植被水分利用效率的累积效应。结果表明:干旱对植被水分利用效率的累积影响可利用多尺度SPEI和植被水分利用效率之间具有最大显著相关性的月份来衡量;黄河流域多年平均植被水分利用效率呈北低南高的分布格局,与多年平均植被总初级生产力的空间分布呈现一定的相似性,植被水分利用效率呈上升趋势,主要原因是植被总初级生产力增速大于蒸散发增速;干旱对黄河流域内58.48%区域的植被水分利用效率存在累积效应,其中累积时间尺度为1~2月、6~8月和19~24月尺度的占比分别达到了43.58%、23.10%和16.96%;干旱对植被水分利用效率的累积时间尺度因植被类型和水文气候条件而异,干旱对北部靠近沙漠区域的草地和农田的累积影响是长期(>18月)的,对湿润半湿润区的草地和森林的累积影响是短期(≤4月)的;平均累积时间尺度随着年均SPEI的增加而下降,SPEI越大,干旱对植被水分利用效率的累积时间尺度越短。

Using gross primary productivity(GPP)of vegetation and evapotranspiration(ET)data,combined with standardized precipitation evapotranspiration index(SPEI)data,the variation characteristics of vegetation water use efficiency(WUE)in the Yellow River Basin from 1982 to 2018 were revealed,and the cumulative effect of drought on vegetation WUE were quantified.The results indicate that the cumulative impact of drought on WUE can be measured by the months with the most significant correlation between multi-scale SPEI and WUE.The annual average WUE shows a distribution pattern of low in the north and high in the south,showing a certain similarity to the spatial distribution of annual average GPP.The WUE shows an upward trend,mainly because the GPP growth rate is greater than the ET growth rate.Drought has a cumulative effect on 58.48%area of vegetation WUE in the Yellow River Basin,with cumulative time scales of 1~2 months,6~8 months,and 19~24 months accounting for 43.58%,23.10%,and 16.96%,respectively.The cumulative time scale of drought on WUE varies depending on vegetation types and hydrological and climatic conditions.The cumulative impact of drought on grasslands and farmland near desert areas in the north is long-term(>18 months),while the cumulative impact on grasslands and forests in humid and semi humid areas is short-term(≤4 months).The average cumulative time scale decreases with the increase of annual average SPEI,and the larger the SPEI,the shorter the cumulative time scale of drought on vegetation WUE.