Exploring evapotranspiration changes in a typical endorheic basin through the integrated observatory network

Abstract The Heihe River Basin (HRB), with unique landscapes and coexisting cold and arid regions, is the second largest endorheic basin in northwestern China. The Heihe integrated observatory network was established in 2007, which included multi-element, multiscale, distributed, and incorporating satellite-airborne-ground based observations via Internet of Things technology; these observations span the main land cover of the basin. This observatory provides a great opportunity to analyze the spatiotemporal variation in evapotranspiration (ET) in the HRB, and ET characteristics were investigated on three scales (typical ecosystems, oasis-desert systems, watershed) taking the HRB as a research object. The average annual ET in typical ecosystems is approximately 380–530 mm upstream (alpine meadow, Qinghai spruce, shrub), 640–1000 mm midstream (maize, wetland), 610–680 mm downstream (riparian forest), and 190 mm and 50 mm in midstream and downstream desert surfaces, respectively. The ET from plant surfaces is strongly controlled by available energy in upstream and midstream regions, while it is controlled by vapor pressure deficit (VPD) and surface conductance downstream. The ET in oasis and desert systems is characterized by three gradients: plant, residential area/barren land, and desert, with a maximum difference of annual ET more than 500 mm. This difference is primarily caused by variations of soil moisture among different underlying surfaces. For watershed ET, higher ET was observed upstream, and it decreased from midstream to downstream, with the highest values in the oasis. The annual ET in the main plant surfaces was approximately 500–700 mm, 600–800 mm, and 600–700 mm in the up-, mid-, and downstream regions, respectively, while the ET was approximately 100–250 mm and 50–200 mm in desert and barren or sparsely vegetation surfaces in the mid- and downstream regions, respectively. The spatiotemporal variations of ET were primarily influenced by land cover, soil moisture, vegetation condition and available energy. The results improve our understanding of the spatiotemporal variations in ET in the HRB and apply to comparable endorheic basins with similar climatic and landscape conditions.