Analysis of Spatiotemporal Distribution of Evaporation Fractions of Different Vegetation Types Based on FLUXNET Site

Evaporative fraction (EF) is the proportion of latent heat flux in surface net energy and reflects the moisture status of an ecosystem. However, the effects of different meteorological factors and vegetation changes on EF are not known. In this study, 142 flux tower observations were used to analyze the spatial and temporal variations of EF in different vegetation types and to analyze the response of meteorological factors and vegetation changes to EF. The results showed that evergreen broadleaf forests (EBFs) had the highest multiyear mean EF (0.61), while open shrublands (OSH) had the lowest multiyear mean EF (0.32). Areas with higher EF values were generally found in temperate continental, mediterranean, and oceanic climates. Seasonally, EFs were generally high in the northern and southern hemispheres during the summer and relatively low in the spring and autumn. The correlation analysis showed that EF increased significantly with increasing precipitation and leaf area index (LAI) for all six vegetation types. Deciduous broadleaf forests ( R = 0.37, RSS = 6.96, and P < 0.01) and wetlands ( R = 0.26, RSS = 7.03, and P < 0.01) showed a significant increasing trend with increasing vapor pressure deficit (VPD), and two vegetation types, grasslands ( R = -0.35, RSS = 13.44, and P < 0.01), and EBF ( R = -0.19, RSS = 3.77, and P < 0.01) showed a significant decrease trend with increasing VPD. The monthly mean EF of three vegetation types, grasslands ( R = 0.26, RSS = 14.20, and P < 0.01), deciduous broadleaf forests ( R = 0.34, RSS = 7.11, and P < 0.01), and wetlands (R = -0.40, RSS = 6.37, and P < 0.01) decreased significantly with increasing wind speed. Our findings provide a scientific basis for assessing surface water conditions and contribute to the understanding of EF interactions with climate and vegetation change.