2001-2015年伊犁河谷草地蒸散发时空变化分析

Spatiotemporal Variation of Evapotranspiration in the Grassland of Yili Valley from 2001 to 2015

蒸散发(Evapotranspiration,ET)是陆地生态系统环境调节的重要方式。草地退化背景下,研究草地蒸散发的时空变化,对掌握草退化生态效应具有重要意义。选择草地退化严重的伊犁河谷作为研究区,利用2001—2015年MODIS ET和NDVI遥感数据以及气温和降水站点数据,借助于GIS空间分析技术,反演植被覆盖度,插值生成气温和降水空间分布数据,进而进行差值和相关性计算,对该区草地ET时空变化及其影响因素进行分析和探讨。结果表明:(1)伊犁河谷草地多年平均ET为395.74 mm;空间上43.21%区域ET位于400~500 mm;全区ET不仅海拔分异明显,且与覆盖度的空间分异总体一致;(2)近15 a伊犁河谷全区草地平均ET减少11.06%,空间上ET发生减少面积占到98.07%,其中51.82%的减少比例位于10%~20%,主要分布在海拔较低的洪积平原和低山区;(3) 2011—2015年时段ET变化的空间分异发生较大转变,低海拔区ET减少比例明显缩减,而高海拔区ET减少比例扩大;(4)伊犁河谷草地植被覆盖度与ET的相关性最高,植被覆盖度是决定草地ET空间分布及时空变化的关键因素,降水对草地ET空间分布及变化的影响高于气温。伊犁河谷植被覆盖度、降水及气温的降低均构成草地ET降低的驱动因素,但复杂的地形使伊犁河谷草地ET与其影响因素的相关性呈现明显且多样的空间差异。

Evapotranspiration(ET)is an important way of environmental regulation in terrestrial ecosystems.Under the background of grassland degradation,study on the spatiotemporal changes of grassland ET is of great importance for grasping the ecological effects of grassland degradation.Based on remote sensing data of MODIS ET and NDVI and station data of temperature and precipitation,and using technologies and methods of spatial analysis of GSI,inversion of grassland coverage,interpolation of temperature and precipitation and calculation of difference and correlation,we chose the Yili Valley,featured with serious grassland degradation,as the study area,and analyzed and discussed the spatiotemporal variation of grassland ET from 2001 to 2015 and its influencing factors.The results showed that:(1)the annual average ET of grassland in Yili Valley was 395.74 mm,and ET of the 43.21%grassland was 400~500 mm;ET showed obvious spatial differentiation along elevation,and the spatial differentiation was consistent with the spatial differentiation of coverage;(2)in the past 15 years,ET in grassland of Yili Valley had decreased by 11.06%in total;spatially,98.07%of the grassland ET decreased at various degrees,among which ET of 51.82%of the total grassland decreased by 10%~20%,and mainly located in the flood plain and low mountain areas;(3)during the period of 2011—2015,the spatial differentiation of the ET change altered obviously,the proportion of ET reduction in low altitude areas decreased while that in high altitude areas increased;(4)the correlation between vegetation coverage and ET was the highest in Yili Valley;coverage was the key factor to determine the spatial distribution and temporal change of grassland ET.The effect of precipitation on the spatial distribution and change of grassland ET was higher than that of air temperature.The decrease of vegetation coverage,precipitation and temperature in the Yili Valley constituted the driving factors for the decrease of grassland ET in together.However,the complex terrain made the correlation between grassland ET and its influencing factors present obvious and diverse spatial differences.