Seasonal Evapotranspiration Changes (1983–2006) of Four Large Basins on the Tibetan Plateau

Abstract:

Lack of reliable historical basin-scale evapotranspiration (ET) estimates is a bottleneck for water balance analyses and model evaluation on the Tibetan Plateau (TP). This study looks at four large basins on the TP to develop a general approach to estimate historical monthly ET. Five existing global ET products are evaluated against monthly ET estimated by the water balance method as a residual from precipitation (P), terrestrial water storage change and discharge (R). The five ET products exhibit similar seasonal variability, despite differences among them. A bias correction method, mainly depending on the probability distribution mapping, effectively removes nearly all biases and significantly increases the reliability of the estimates. Then, the surface water balance changes over the four basins are analyzed based on the corrected ET products as well as observed P and R during 1983–2006. A trend analysis shows an upward trend for ET in the four basins for all seasons during the past three decades, which is consistent with regional warming. For the upper Yangtze River basin, Qiangtang Plateau, and Qaidam basin, P exhibits increasing trend in all seasons with the largest increase in summer; ET also displays increasing trends in all seasons. For the upper Yellow River basin, both of P and R display consistently decreasing trends in summer, while increasing of P and decreasing of R in other seasons.