Potential Evapotranspiration Characteristic and Its Abrupt Change Across the Qinghai-Tibetan Plateau and Its Surrounding Areas in the Last 50 Years

Daily routine observation data from 274 meteorological stations in the Qinghai-Tibetan Plateau and its surrounding areas from 1970 to 2017 were utilized to examine the spatial patterns and abrupt changes of potential evapotranspiration with the formula of FAO Penman-Monteith, in consideration of China’s eco-geographical divisions. The results showed that \mathrm{①} annual and seasonal average potential evapotranspiration, except for summer and winter, displayed a distinct spatial pattern in the Qinghai-Tibetan Plateau and its surrounding areas, with higher values in the north and south but lower values in the middle; the time when monthly potential evapotranspiration reached its maximum or minimum showed clearly zonal differences, namely earlier in the south and later in the north. \mathrm{②} The prevailing mean and trend abrupt changes of potential evapotranspiration were observed in the study area, while there were large differences in the abrupt change time in different regions and seasons. Specifically, the mean abrupt change was dominated by positive mutation, with generally the earliest abrupt change time occurring in spring and the latest appearing in winter; the trend abrupt change pattern was mainly described as the process shifting from a downward trend to an upward trend, the trend change points in year, spring, autumn and winter were postponed gradually from the northeast to the southwest with a delay of about 20, 10, 20 and 5 years, respectively. Comparatively, the abrupt change time of potential evapotranspiration trend in the whole plateau was later than that in the whole buffer zone, with a respective lag of 5, 1, 12, 5 and 4 years. \mathrm{③} Corresponding to the periodic change of potential evapotranspiration, significant evaporation paradox only scattered through the study area during the period before the trend change point (2007), but it was absent afterwards and would not appear in the future. The above findings will provide a scientific basis for further understanding the climate change and eco-hydrological process of the Qinghai-Tibetan Plateau and its surrounding areas in global warming.