Assessing the effect of climate change on reference evapotranspiration in China

Reference evapotranspiration (ET ₀ ) is a key parameter in hydrological and meteorological studies. In this study, the FAO Penman–Monteith equation was used to estimate ET ₀ , and the change in ET ₀ was investigated in China from 1960 to 2011. The results show that a change point around the year 1993 was detected for the annual ET ₀ series by the Cramer’s test. For the national average, annual ET ₀ decreased significantly (P < 0.001) by ?14.35 mm/decade from 1960 to 1992, while ET ₀ increased significantly (P < 0.05) by 22.40 mm/decade from 1993 to 2011. A differential equation method was used to attribute the change in ET ₀ to climate variables. The attribution results indicate that ET ₀ was most sensitive to change in vapor pressure, followed by solar radiation, air temperature and wind speed. However, the effective impact of change in climate variable on ET ₀ was the product of the sensitivity and the change rate of climate variable. During 1960–1992, the decrease in solar radiation was the main reason of the decrease in ET ₀ in humid region, while decrease in wind speed was the dominant factor of decreases in ET ₀ in arid region and semi-arid/semi-humid region of China. Decrease in solar radiation and/or wind speed offset the effect of increasing air temperature on ET ₀ , and together led to the decrease in ET ₀ from 1960 to 1992. Since 1993, the rapidly increasing air temperature was the dominant factor to the change in ET ₀ in all the three regions of China, which led to the increase in ET ₀ . Furthermore, the future change in ET ₀ was calculated under IPCC SRES A1B and B1 scenarios with projections from three GCMs. The results showed that increasing air temperature would dominate the change in ET ₀ and ET ₀ would increase by 2.13–10.77, 4.42–16.21 and 8.67–21.27 % during 2020s, 2050s and 2080s compared with the average annual ET ₀ during 1960–1990, respectively. The increases in ET ₀ would lead to the increase in agriculture water consumption in the 21st century and may aggravate the water shortage in China.