Attribution analyses of reference evapotranspiration changes in China incorporating surface resistance change response to elevated CO2.

• A modified Penman-Monteith method incorporated the CO 2 effect on surface resistance. • Historical and future variations in ET 0 and their attribution were examined. • The dominant factor shifted from wind speed to maximum air temperature after 1993. • The future changes in ET 0 could be dominated by maximum air temperature. Reference evapotranspiration (ET 0) is a key component of the water cycle. In this study, a modified Penman–Monteith method incorporating the CO 2 effect on surface resistance was used to estimate past change in ET 0 in China for 1961–2019 and to project future changes for 2040–2099. A partial-differential equation was used to attribute the changes in ET 0. Results indicated the following. (1) A shift point in the annual ET 0 series occurred in 1993, in which annual ET 0 in China had been decreasing and then increased significantly by −18.93 and 11.19 mm·decade-1 before and after 1993, respectively, with ET 0 having changed most drastically within the temperate continental climate zone. (2) Wind speed and solar radiation were the major dominant factors responsible for the change in ET 0 during 1961–1992, and their contribution rates were 48.30 and 38.92 %, respectively. During 1993–2019, increasing maximum air temperature was the dominant factor contributing to increasing ET 0 , with a contribution rate of 81.71%, yet wind speed was the dominant factor affecting ET 0 changes at 45% of the stations in China. (3) In future projections, maximum air temperature is expected to be the dominant factor influencing the increase in ET 0 , the values of which were projected at 1.49 and 16.05 mm·decade-1 during 2040–2099 under RCP4.5 and 8.5 scenarios, respectively, with projections from five GCMs. The increasing surface resistance response to elevated CO 2 was found to be an important contributor to the decrease in ET 0. Particularly for the RCP8.5 scenario, the increase in surface resistance was found to lead to the decrease in ET 0 by −0.68 mm·year−1 (-42.37%). This suggests that historical and future tendencies towards aridity in China may be considerably weaker and less extensive than previously assumed. [ABSTRACT FROM AUTHOR]