Contribution of vegetation change to the surface radiation budget: A satellite perspective

Abstract

Abstract The surface radiation budget is of crucial importance to ecosystem evolution but varies with complex atmospheric and surface conditions. Vegetation change alters the surface thermal properties and the subsequent radiation budget; however, the vegetation contribution is difficult to isolate from mixed influences. Based on satellite observations, we apply a novel trajectory-based approach to detect the impact of vegetation change on the global surface radiation variation in recent decades (2001–2016). Satellite data on radiation and vegetation available from the Clouds and the Earth's Radiant Energy System (CERES) and Moderate Resolution Imaging Spectroradiometer (MODIS) instruments are adopted for this investigation. Methodologically, the surface net radiation (Rn) in the nonchanged vegetation trajectory represents the synthetic result of atmospheric influences and serves as a reference for isolating Rn variations due to vegetation change. The results demonstrate that the multiyear mean of global Rn is 71.57 W·m−2 with an increasing trend of 0.053 W·m−2·yr−1. Vegetation change contributes an additional 0.047 W·m−2·yr−1 of radiation in greening regions, accounting for 53.36% of the total increase in Rn. Spatially, the contribution of vegetation presents significant variability, with positive contributions located mainly in western Europe and southern Africa and negative contributions located mainly in parts of Asia and eastern Australia. Physically, the influence of vegetation change on the surface radiation budget originates from its alteration of albedo and emissivity, particularly the former. Specifically, a 1% increase in the normalized difference vegetation index (NDVI) is expected to reduce albedo by −0.003 and increase surface net shortwave radiation by 0.86 W·m−2. It can be concluded that the change in albedo by vegetation change has a nonnegligible influence on the surface radiation budget in different regions. These results help capture the physical mechanism responsible for the evolution of Earth's radiation and support environmental management.