Spatial-Temporal Patterns of Evapotranspiration Along an Elevation Gradient on Mount Gongga, Southwest China

Evapotranspiration (ET) is a crucial component of the hydrological cycle in terrestrial ecosystems, but estimating ET in mountainous regions is challenging. In this study, the performance of a generalized nonlinear formulation of the complementary principle while estimating daily ET was evaluated, and the spatial-temporal variation of ET was analyzed across four vegetation types along an elevation gradient on Mount Gongga, Southwest China. The values of the calibrated Priestley and Taylor coefficients for each of the four sites ranged from 0.98 to 1.13. The correlation coefficients between the estimated and observed daily actual evapotranspiration for each of the four sites ranged from 0.71 to 0.92. A markedly asymmetrical complementary relationship existed among the four studied sites, and the values showed less scattered during the wet season. The annual ET rates were 779.12, 781.63, 701.77, and 625.17 mm/yr in the broadleaf forest (BLF), broadleaf and coniferous mixed forest (BCF), coniferous forest (CF), and shrub land (SL), respectively, and showed a decreasing trend of 9.72 mm per 100 m along the elevation gradient. After recalibration of the seasonal (e) values, the estimated annual ET rates increased and were closer to the observed values in BLF and BCF. The results indicate that daily ET in mountainous areas can be estimated using the generalized nonlinear formulation of the complementary relationship together with routine meteorological data alone, but seasonal changes in (e) values should be taken into consideration in forests with deciduous trees.