Researchers Estimate Potential Evapotranspiration over the Past 50 years in the Arid Region of Northwest China

Evapotranspiration is a key process in the Earth’s surface hydrological cycle and energy balance. The temporal variation of evaporation is an important indicator of climate change and the response of water resource and eco-environment to such change. Estimation of evapotranspiration is necessary for improving the planning, management, and efficient use of water resources. Since directly measuring evaporation is difficult, potential evapotranspiration (ET₀) has been widely used in water resource studies and management practice.

Based on the long-term meteorological data collected at 81 ground-based meteorological stations of the China Meteorological Administration during the period 1958–2010, LI Zhi et al. estimated the ET₀ and analyzed the corresponding trend attribution in Northwestern arid region of China. They also investigated the relationship between ET₀ and several climatic variables in the context of global climate change, and focused on the recent changes and attribution of ET₀ in arid region of Northwest China.

Daily observations on temperature (including minimum, maximum and average) at 2 m height, sunshine duration and wind speed at 10 m height, precipitation, and relative humidity from 1958 to 2010 were used in analysis of ET₀ in this region. The Penman–Monteith method and Mann–Kendall test were used to estimate daily mean ET₀ and detect trends in ET₀ and related meteorological factors, respectively. A non-dimensional complete correlation analysis was also conducted to identify main factors influencing ET₀.

The analysis result showed that the ET₀ has exhibited an obvious decreasing trend until the early 1990s. However, the downward trend has been reversed to an upward trend after then. Decrease in diurnal temperature range and wind speed may lead to the decrease of ET₀ during 1956–1993. The change of dominant factors in the ET₀ trend has differences after the early 1990s, and observed increase in wind speed was the primary factor contributing to the reversion of ET₀. The result was published in Hydrological Processes on 30 January 2014.