近20年黄土高原NDVI/气象要素对实际蒸散发的影响研究

Effects of NDVI/Meteorological Elements on Actual Evapotranspiration in Loess Plateau over Last 20 Years

退耕还林还草工程使黄土高原植被覆盖度显著增加,同时全球气候持续变暖,在此双重背景下,研究黄土高原蒸散发(Evaporation,ET)的时空分布规律及NDVI和气象要素对蒸散发的综合影响,对该地区水资源综合治理具有一定的指导意义。基于MOD16A2 ET、MOD13Q1 NDVI和气象数据,采用空间回归分析、Morlet小波分析、主成分分析等方法,探讨了黄土高原2001—2020年ET全年、生长季、非生长季3个时段时空演变特征及NDVI和气象因子的综合影响。结果表明:①3个时段内ET均显著增加,增速分别为全年>生长季>非生长季,且均存在14 a的第一主周期,全年及生长季的ET值由东南向西北递减,非生长季ET数值全年最低,较高值分布于西部和南部,ET值年际变化空间分布与ET值空间分布保持一致;②3个时段NDVI均显著增加,值的空间分布与ET值空间分布一致,降水量在全年及生长季显著增加,非生长季增加不明显,温度与风速在3个统计时段无明显增加趋势,降水和温度空间分布规律与ET基本一致;③不同时段各影响因子对ET值变化贡献大小不同,生长季风速、气温和NDVI对其有较大贡献,非生长季NDVI、降水和气温贡献较大,全年中贡献较大的为NDVI和降水。

Given that the Grain for Green Program significantly enhances the vegetation coverage in the Loess Plateau and that global warming keeps worsening,studying the spatio-temporal distribution law of the evapotranspiration(ET)in the Loess Plateau and the combined influences of the normalized difference vegetation index(NDVI)and meteorological elements on the ET can guide the comprehensive management of the water resources in the plateau.Spatial regression analysis,Morlet wavelet analysis,and principal component analysis are performed to examine the spatio-temporal evolution characteristics of the ET in the Loess Plateau during the three periods of the whole year,the growing season,and the non-growing season over 2001—2020 and the combined influences of NDVI and meteorological elements with MOD16A2 ET,MOD13Q1 NDVI,and meteorological data.The results support the following conclusions:①ET increases significantly in all the three periods,with the growth rate for the whole year higher than that for the growing season and much higher than that for the non-growing season.The three periods all have a first main cycle of 14 a.ET decreases from southeast to northwest both in the whole year and the growing season,and the ET in the non-growing season is lower than that in the whole year and that in the growing season.The higher value is in the west and the south,and the spatial distribution of the interannual variation of ET is consistent with that of ET.②NDVI also increases significantly in all the three periods,and the spatial distribution of its value is consistent with that of ET.Precipitation increases remarkably in the whole year and in the growing season,with no marked growth in the non-growing season.No obvious increase trends in temperature and wind speed are observed in the three statistics periods.The spatial distribution laws of precipitation and temperature are largely consistent with that of ET.③The contribution of each influencing factor to the change in ET varies with the period.Specifically,the first principal factors in the growing season,the non-growing season,and the whole year are respectively wind speed,temperature,and NDVI,NDVI,precipitation,and temperature,and NDVI and precipitation.