Elevation‐dependent changes in reference evapotranspiration due to climate change
Juying Sun, Genxu Wang, Xiangyang Sun, Shan Lin, Zhaoyong Hu, Kewei Huang
Abstract
Abstract The Food and Agriculture Organizations' (FAO) Penman–Monteith reference evapotranspiration (ET 0 ) is a crucial index in the research of water and energy balance. Temporal and spatial variations in ET 0 from 1981–2017 were investigated in the Hengduan Mountains, China . The results showed a change point around the year 2000 in ET 0 series. ET 0 decreased and increased significantly by +3.200 mm/year ( p < 0.01) from 1981–2000 and by +4.109 mm/year ( p < 0.01) from 2001–2017, respectively. The contribution analysis shows that the positive significant contribution of air temperature (TA) was offset by negative effects of decreases in downward shortwave radiation (R s ) and wind speed (WS) and an increase in actual vapour pressure (e a ), causing the decrease in ET 0 from 1981 to 2000. WS was the largest contributing factor for the decrease in ET 0 from 1981 to 2000 during spring, winter and annually, while R s and e a were the largest negative contributors in summer and autumn, respectively. An increase in TA was responsible for the increase in ET 0 in all seasons except winter and the annual scale in 2001–2017. The sensitivity analysis shows that ET 0 was most sensitive to TA, and WS was the least sensitive variable. The trends of ET 0 increased with elevation; we denote this as the elevation‐dependence of ET 0 changes. The elevation‐dependence was also noted for the trends of WS and e a , with higher elevations showing larger changes in WS and lower changes in e a . Besides, the sensitivities of TA, R s and e a decreased with elevation, while that of WS increased slightly with elevation. A comprehensive investigation into the trends of climatic drivers and their sensitivities revealed complex trends of the contributions of climatic variables on ET 0 with elevation, with no uniform trend existed in seasons. The results will contribute to our understanding of the response of ET 0 to climate change in a mountainous area, and provide a guideline for the water resources management under climate change.