中国西北干旱区蒸散发时空动态特征

利用MODIS ET数据集中2000—2014年的地表实际蒸散发量产品,运用变异系数、Theil-Sen median趋势分析与MannKendall检验和Hurst指数法,研究了中国西北干旱区蒸散发的空间格局、不同维度的空间异质性和时间变化特征及未来趋势预测。结果表明:(1)2000—2014年全区蒸散发量总体较小,蒸散发量小于200 mm的区域占总面积的38.329%。在空间上ET自山区向两侧平原减少,不同土地覆盖的ET大小为:林地农用地草地稀疏植被。受降水和土地覆盖的综合影响,ET的高值区(400 mm)主要在降水丰富的山区林地和草地,而低值区(200 mm)主要在降水较少的平原稀疏植被区和草地。(2)近15年全区蒸散发变异程度不明显,以相对较低的波动变化为主。各亚区内波动较低区域的比例为:北疆天山祁连山内蒙西部河西走廊南疆。(3)15年间全区年均蒸散发量呈波动变化,总体有微弱的减小趋势,变化率为-0.9348 mm/a。基于像元尺度的分析也表明全区ET以减小的变化趋势为主,但各亚区的减小程度各异:天山内蒙西部河西走廊北疆祁连山,仅南疆有增加趋势。(4)全区ET的Hurst指数均值为0.689,Hurst指数大于0.5的范围所占比例为80.033%,未来全区蒸散发的变化趋势以持续性减小为主。其中22.003%区域的变化趋势无法确定。未来各亚区ET的减少趋势为:内蒙西部天山河西走廊北疆祁连山南疆。

Temporal-spatial dynamic change characteristics of evapotranspiration in arid region of Northwest China

Using MODIS ET data of actual surface evapotranspiration products that were concentrated between 2000 to 2014, we used variable coefficients, the Theil-Sen median trend analysis, Mann-Kendall test, and Hurst index, to investigate the spatial pattern of evapotranspiration, spatial heterogeneity of different dimensionalities, characteristics of time variation, and future trends considering an arid region in Northwest China. The results showed the following: 1) Evapotranspiration over the entire region was very low from 2000 to 2014, and the area of evapotranspiration, less than 200 mm, accounts for 38.329% of the total area. Evapotranspiration decreases from mountainous areas to the plains. Evapotranspiration data were obtained for different land covers, which are forest land, cropland, grassland, and sparse vegetation, arranged from high to low. Mountain forests and grasslands that receive high rainfall have higher values of evapotranspiration (more than 400 mm) than sparse vegetation plains and grasslands that experience low rainfall (less than 200 mm). 2) The degree of variation in evapotranspiration over the past 15 years for the entire region is not obvious, but shows a slight fluctuation. The proportion of areas with slight fluctuations in each subregion ranged from large to small in the order of Northern Xinjiang, Tianshan Mountain, Qilian Mountain, Western Inner Mongolia, Hexi Corridor, and Southern Xinjiang. 3) The degree of variation in evapotranspiration over the past 15 years for the entire region shows changes in the fluctuations with a weakly decreasing trend, at a change rate of-0.9348 mm/a. An analysis based on the pixel scale also shows a mainly decreasing trend. The degree of decreases in each subregion ranged from large to small in the order of Tianshan Mountain, Western Inner Mongolia, Hexi Corridor, Northern Xinjiang, and Qilian Mountain. Only Southern Xinjiang showed an increasing tendency. 4) The Hurst index average of evapotranspiration for the entire region is 0.689. The area of the Hurst index greater than 0.5 accounts for 80.033% of the total area. The trend of changes in evapotranspiration in the future for the entire region is mainly towards a persistent decrease. However, the trend of changes for 22.003% of the area cannot be determined. The future trend of change in the degree of decreases for each subregion from large to small follows the order of Western Inner Mongolia, Tianshan Mountain, Hexi Corridor, Northern Xinjiang, Qilian Mountain, and Southern Xinjiang.