Elevation-dependent changes in reference evapotranspiration due to
climate change: The case of the Hengduan Mountains, China
Abstract
The Food and Agriculture Organizations’ (FAO) PenmanMonteith reference
evapotranspiration (ET0) index is a key parameter in hydrological and
meteorological studies. Temporal and spatial variations in ET0 from
1981–2017 were investigated in the topographical rapid change zone in
the Hengduan Mountains, China. The results showed a change point around
the year 2000 in the area-averaged annual ET0 series. ET0 decreased and
increased significantly by 3.103 mm/yrmm/year (p < 0.05) from
1981–2000 and by 3.591 mm/yrmm/year (p < 0.05) from
2001–2017, respectively. The contribution analysis shows that reduction
in wind speed (Ws) was the primary driving force for the decrease in ET0
during 1981–2000 in spring, autumn, and winter, and annually, while net
solar radiation (Rn) was the dominant force in summer. Reduction in
relative humidity (RH) was responsible for the increase in ET0 in all
seasons and for the annual scale in 2001–2017. The sensitivity analysis
shows that ET0 was most sensitive to Rn, followed by RH, and air
temperature (Ta) was the least sensitive of the variables. The trends of
ET0 were also found to increase with elevation; we denote this as the
elevation-dependence of ET0 changes. The elevation-dependence was also
noted for the trends of Ws, RH, and Rn, with higher elevations showing
larger changes in these parameters. In addition, the sensitivities of
Rn, RH, and Ta decreased with elevation, while that of Ws increased with
elevation. A comprehensive investigation into the trends of these
climatic variables and their sensitivities revealed complex trends of
ET0 along the elevation gradient, with typical increases with elevation
over the annual scale despite the large differences in seasons. A more
detailed exploration of the mechanisms causing this pattern is required.