The variations in potential evapotranspiration and the effects of
environmental changes in a humid subtropical region
Abstract
Potential evapotranspiration (ETp) measures the ability of the
atmosphere to remove water from the surface by evaporation and
transpiration. Because the reference evapotranspiration is often used to
infer this ability, ETp is usually considered only influenced by
meteorological conditions. Due to the close linkages within the
soil-vegetation-atmosphere system, ETp is likely influenced also by
surface conditions like soil water content and vegetation cover.
Therefore, this study is aimed at investigating the relationships
between ETp and the associated environmental variables at different time
scales. The results show that ETp has increased significantly by
~2.4 mm yr-1 during 1982-2015, alongside significant
increase in vegetation index (NDVI), wind speed (Ws), temperatures and
significant decrease in relative humidity (RH). Linear trends varied
across seasons but similarities were found between spring and winter and
between summer and autumn. Summer saw the greatest changes in ETp per
unit change in environmental variables, which implies a likelihood of
greater water demand with a warmer summer. Solar radiation, RH and
precipitation exerted overall stronger influence on ETp
(R2>0.50) than other factors, and NDVI and SWC was found
positively and negatively affecting ETp at all time scales
(p>0.05 only for ETp-NDVI at annual scale). Furthermore,
partial correlation analysis showed significant effects of NDVI and SWC
on ETp at the monthly scale and SWC also influenced ETp in summers
(p<0.05). This study proves that ETp is related to surface
conditions in addition to meteorology, and shows the major factors
effectively explaining the changes in ETp across different time scales.