Potential evapotranspiration (ET₀) is an integral component of the hydrological cycle and the global energy balance, and its long-term variation is of much concern in climate change studies. The Loess Plateau is an important area of agricultural civilization and water resources research. This study analyzed the spatial and temporal evolution processes and influential parameters of ET₀ at 70 stations in different topographical areas of the Chinese Loess Plateau (CLP). Using the Mann–Kendall trend, Cross wavelet transform, and the ArcGIS platform, the ET₀ of each station was quantified using the Penman–Monteith equation, and the effects of climatic factors on ET₀ were assessed by analyzing the correlation coefficients and contribution rates of the climatic factors. The results showed that: (1) the overall trend of the ET₀ in different terrains of the Loess Plateau is consistent, however, the ET₀ values differ; the hill region (HR) has the highest ET₀, followed by the valley region (VR), and the mountain region (MR) has the lowest, and ET₀ changes differ between seasons. (2) Spatial distribution characteristics of multiyear mean ET₀ in the study are as follows: the ET₀ values in mountain and hilly areas are decreasing from west to east, and the higher mean annual ET₀ value in the VR is mainly concentrated in the eastern CLP. (3) In the past 58 years, the annual mean and the seasonal ET₀ of the region showed increasing trends, however, differences in different terrains were obvious. (4) ET₀ has significant correlations with El Niño–Southern Oscillation (ENSO), Pacific–North American teleconnection (PNA), and Atlantic Multidecadal Oscillation (AMO). The resonance period of ET₀ and ENSO was 3–6 a, mainly in 1976–1985. The mean coherence phase angle was close to 360°, indicating that ET₀ lags behind PNA by approximately 2–6 a; ET₀ has a very strong positive correlation with AMO. (5) Relative humidity (RH) is the main influencing factor of ET₀ change in the Loess Plateau. Temperature (T) variation has the highest contribution rate (42%) to the regional ET₀ variation in the entire CLP. We should pay more attention to the variation of evaporation under future climate change, especially temperature change.

The exchange of heat and water vapor between land surface and atmosphere over the Third Pole region (Tibetan Plateau and nearby surrounding region) plays an important role in the Asian monsoon, westerlies and the northern hemisphere weather and climate systems. Supported by various agencies in the People’s Republic of China, a Third Pole Environment (TPE) Observation and Research Platform (TPEORP) is now implementing over the Third Pole region. The background of the establishment of the TPEORP, the establishing and monitoring plan of long-term scale (5–10 years) of it will be shown firstly. Then the preliminary observational analysis results, such as the characteristics of land surface energy fluxes partitioning and the turbulent characteristics will also be shown in this study. Then, the parameterization methodology based on satellite data and the atmospheric boundary layer (ABL) observations has been proposed and tested for deriving regional distribution of net radiation flux, soil heat flux, sensible heat flux, and latent heat flux (evapotranspiration (ET)) and their variation trends over heterogeneous landscape of the Tibetan Plateau (TP) area. To validate the proposed methodology, the ground-measured net radiation flux, soil heat flux, sensible heat flux and latent heat flux of the TPEORP are compared to the derived values. The results show that the derived land surface heat fluxes over the study areas are in good accordance with the land surface status. These parameters show a wide range due to the strong contrast of surface features. And the estimated land surface heat fluxes are in good agreement with ground measurements, and all the absolute percent difference is less than 10% in the validation sites. The sensible heat flux has increased slightly, and the latent heat flux has decreased from 2001 to 2016 over the TP. It is therefore concluded that the proposed methodology is successful for the retrieval of land surface heat fluxes over heterogeneous landscape of the TP area. Further improvement of the methodology and its applying field over the whole Third Pole region were also discussed.