西北干旱区河西走廊荒漠绿洲土地覆盖类型与蒸散的关系研究——基于Landsat 8和ZY3数据融合

蒸散是地表水热平衡的重要分量,也是陆地生态过程与水文过程之间的重要纽带,尤其在干旱区地-气相互作用、碳循环、水循环等过程所包含的物质与能量交换中占有极其重要的地位。基于Landsat 8遥感影像和资源三号影像(ZY3)的高分辨率植被信息,利用SEBS模型对西北干旱区河西走廊中段临泽绿洲北部区域地表蒸散量进行了估算,并用绿洲内部和绿洲-荒漠过渡带两个通量塔涡动相关数据对模型进行评估,分析了不同土地覆盖类型对蒸散量空间分布的影响。结果表明:(1)SEBS模型模拟值与实测日蒸散值之间拟合效果较好,且在均一地表时(绿洲农田区)估算精度更高(R~2=0.96,P0.001),RMSE、MAE分别为0.84 mm/d、0.56 mm/d;(2)从季节变化来看蒸散量与作物生长密切相关,夏季灌溉和降雨使得研究区水分充足,植被覆盖度高,蒸散量相应增加,在绿洲地区可达5.95 mm/d,而冬季最小仅为0.52 mm/d;(3)从蒸散量的空间变化来看,水体蒸散值最大,其余依次为农田、防护林、裸地和灌木丛,说明除水体外,随着植被覆盖的增大,蒸散量也逐渐增加。通过ZY3影像的高分辨率植被信息与Landsat 8影像热红外数据融合,提高了SEBS模型对该区域蒸散量的模拟效果,增进了我们对绿洲下垫面与大气间水热交换规律、水文过程、生态-水文相互作用的深入理解。

Relationship between land cover type and evapotranspiration on the basis of Landsat 8 and ZY3 data fusion approach for a desert oasis in the middle Hexi corridor area of the arid regions of northwestern China

Evapotranspiration is a major component of water and heat exchange in terrestrial ecosystems, as it acts as a critical link between ecological and hydrological processes, particularly for the exchange of mass and energy involved in land surface-air interaction, carbon cycle, and hydrological cycle in arid regions. In this study, we used Landsat 8 remote-sensing images and resources NO.3 (ZY3) images, with high-resolution vegetation information, and surface energy balance system (SEBS) model to estimate surface evapotranspiration (ET) in a desert oasis in the middle Hexi corridor area of the arid regions of northwestern China. We compared the estimated ET values with the measured values by using the eddy covariance method. We also spatially analyzed the effects of land cover types on ET. The main results of this study indicated that (1) the estimated daily ET was consistent with the corresponding measured values, especially for homogeneous underlying surface such as oasis (R²=0.96, P < 0.001) with low values of RMSE (0.84 mm/d) and MAE (0.56 mm/d). (2) In terms of seasonal changes, ET is closely related to phonological period, highest in summer, followed by spring, autumn, and winter (e.g., daily ET was 5.95 mm/d for cropland within the oasis, as opposed to 0.52 mm/d in winter), because of the peaked plant cover and summer rainfall in this study area. (3) With respect to spatial variations in ET, the surface ET for water body was the highest, followed by those for cropland, shelterbelt, bare land, and shrubland; this suggested that evapotranspiration also increases gradually with the increase in plant cover, except for water body. In addition, performance of the SEBS model for estimating ET in this region was fairly good when applying the data fusion of high-resolution vegetation information of ZY3 and thermal infrared data of the Landsat 8 remote-sensing images was performed. All these results have enhanced our understanding of the patterns of water and heat exchange between the underlying surface and atmosphere, which play a key role in hydrological and ecological processes or interaction between ecological and hydrological processes locally in arid desert oasis area. Our findings may provide some scientific insights into the decision-making for rational water utilization by the local government.