Assessing the effect of climate change on reference evapotranspiration in China

摘要

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.