Determining factors in potential evapotranspiration changes over China in the period 1971-2008

Potential evapotranspiration (ET (o)) is important to hydrological cycling and the global energy balance. Based on a modified FAO56-Penman-Monteith model, ET (o) was simulated for 603 meteorological stations across China in the period 1971-2008. Spatial distribution and temporal change of ET (o) were characterized, and the determining factors in ET (o) were revealed by sensitivity analysis. Results show obvious regional differences in annual average ET (o) and its determining factor. In general, annual average ET (o) decreased in the period 1971-2008, but increased since the 1990s. Wind speed and sunshine duration were determining factors in the annual ET (o) trend, with smaller contributions from relative humidity and temperature. Declining wind speed was the determining factor in decreasing annual ET (o) in northern temperate regions and the Tibetan Plateau. The spatial extent of wind speed influence contracted to northwest China in summer, and expanded to the whole country in autumn. Decreasing sunshine duration was the determining factor in decreasing annual ET (o) in subtropical and tropical regions, especially in summer, with a larger spatial influence mainly to the southeast of the farming-pastoral region. ET (o) change has distinct impacts on earth surface ecosystems and environment depending on different determining factors.