As the second largest inland river in China, the Heihe River Basin, is a very important water resource for irrigated agricultural areas in the Hexi Corridor of Gansu province. Therefore, it is extremely necessary to monitor spatiotemporal variations in water use irrigated fields with high spatial resolution data and facilitate water resources management and irrigation scheduling in such a water shortage area. 

Evapotranspiration (ET), the sum of land surface evaporation and plant transpiration, is a major component of the water cycle and energy exchange of the soil-vegetation-atmosphere system. 

It is essential for water management nationwide at the field scale to map daily ET over irrigated agricultural areas in the Heihe River Basin at a high spatiotemporal resolution using thermal remote sensing-based models. However, due to the current lack of high spatiotemporal resolution remote sensing data, mapping temporally continuous daily ET seems quite difficult. 

To achieve a continuous spatial distribution of daily ET with a high spatial resolution, a research group headed by HUANG Chunlin from Northwest Institute of Eco-Environment and Resources of the Chinese Academy of Sciences, collaborating with other researchers, has mapped daily ET over irrigated agricultural areas in the Heihe River Basin based on spatiotemporal fusion of the Advanced Space-borne Thermal Emission Reflectance Radiometer (ASTER) and Moderate Resolution Imaging Spectroradiometer (MODIS) images. 

They collected the high spatial resolution data by using various kinds of sensors and analyzed the spatiotemporal characteristics of these data, and compared the time series of daily ET modelled from the Surface Energy Balance System (SEBS) with that modelled from PT-JPL (one of Satellite-based Priestley-Taylor ET models) and observations from eddy covariance (EC) systems. 

Results indicate that regional ET mapping at a high spatiotemporal resolution can be accurately achieved based on the Spatial and Temporal Adaptive Reflectance Fusion Model (STARFM) and Surface Energy Balance System (SEBS).  

The method of mapping daily ET proposed can be applied to long-term series, large research areas, and other satellite images for further verification of its applicability in future studies.  

The results have been published in the journal Agricultural and Forest Meteorology entitled "Mapping daily evapotranspiration based on spatiotemporal fusion of ASTER and MODIS images over irrigated agricultural areas in the Heihe River Basin, Northwest China." 

This work is supported by the National Science Foundation of China, and the Science and Technology Service Network Initiative Project of the Chinese Academy of Sciences. 

  Land use map of the study area and the location of AWS/EC stations (Image by HUANG Chunlin)