Spatial Variability of Daily Evapotranspiration in a Mountainous Watershed by Coupling Surface Energy Balance and Solar Radiation Model with Gridded Weather Dataset

Abstract

The determination of evapotranspiration (ET) using ground-based meteorological data does not adequately capture the spatial patterns of mass and energy fluxes in mountainous areas. In this work, we evaluate the daily spatial distribution of ET over a mountainous watershed in southeastern Brazil by coupling Surface Energy Balance Algorithms for Land (SEBAL), a global solar radiation (GSR) model, and a gridded weather dataset (GWD). To estimate daily tilted GSR, we use the relation between terrain and sun angles over a 24-h integration time. Tests were performed in summer/wet (12 January 2015) and winter/dry (25 September 2015) periods to evaluate the seasonal differences in ET over tilted surfaces. The results indicated different spatial patterns of daily ET on the watershed in each period. In summer, ET was 9.8% higher on slopes facing South, while in winter, ET was 10.6% higher on slopes facing North and East. A high variability in daily ET was found on steeper slopes (above 45°) in both periods. The notable ET spatial heterogeneity indicates the complex partitioning of mass and energy fluxes from different terrain angles, which may influence hydroecological processes at the local scale. The presented approach allowed a more detailed capture of the spatial variability of ET in a mountainous watershed with scarce groundbased data.