Analysis of Evapotranspiration Variation Characteristics and Influencing Factors in Different Regions of the Tibetan Plateau

To explore the characteristics of evapotranspiration (ET) and its main influencing factors at typical stations across different regions of the Tibetan Plateau, and to deepen the understanding of land-atmosphere interactions and eco-hydrological processes in the region, this study selected four representative stations: Muztagh, Naqu, QOMS, and SETS. Based on long-term observational data and satellite remote sensing, we analyzed the actual evapotranspiration at each station across different temporal scales, along with its correlation with meteorological factors. The results are summarized as follows:(1) Annual Variation: The annual evapotranspiration at Muztagh, Naqu, and SETS showed an increasing trend, while a decreasing trend was observed at QOMS. At Muztagh, annual evapotranspiration was significantly correlated with net radiation, while at SETS, it was significantly positively correlated with temperature. No significant correlation was found between the annual evapotranspiration and any meteorological factor at QOMS or Naqu, suggesting that the changes may be influenced by multiple factors. (2) Monthly Variation: Monthly evapotranspiration at all stations exhibited a unimodal pattern. During the monsoon period, evapotranspiration accounted for 71.45% of the annual total at QOMS, the highest among the four stations, followed by Naqu (66.49%), Muztagh (60.81%), and SETS (55.34%). The factors influencing evapotranspiration varied by station: during the monsoon, Muztagh was influenced by soil moisture and net radiation; Naqu was mainly influenced by soil moisture and temperature; QOMS was affected by precipitation and soil moisture, with precipitation having a stronger influence; and SETS was controlled by net radiation. (3) Diurnal Variation: Diurnal evapotranspiration at all stations exhibited an inverted U-shaped curve during different periods. During the monsoon, the peak diurnal evapotranspiration followed the order: Naqu > SETS > Muztagh > QOMS. In contrast, during the non-monsoon period, the sequence was SETS > Naqu > Muztagh > QOMS. Path analysis revealed that the dominant factors influencing diurnal evapotranspiration varied across stations: at Muztagh, evapotranspiration was primarily influenced by net radiation and soil moisture. At Naqu and QOMS, soil moisture was the dominant factor, while at SETS, temperature was the primary influence, followed by net radiation.