Negative impacts of the withered grass stems on winter snow cover over the Tibetan Plateau

Abstract

Along with climate change, the coverage of short vegetation, such as alpine grass over the Tibetan Plateau (TP), has significantly increased in the past decades. However, the changes in non-growing season alpine grass—withered grass stems (WGS), as well as their impact on snow cover and surface energy budget, still remain unclear. In this study, we derived vegetation stem area index (Ls) data by using GLASS's leaf area index (LAI) as a way to analyze the impacts of WGS on snow depth, snow cover fraction, surface temperature and surface albedo in winter (December-January-February) over the TP during the period 1982–2018, and numerical experiments were conducted by the Community Land Model version 5.0 (CLM5.0) to investigate physical mechanism behind impacts of WGS. The results reveal that an increment in WGS coverage significantly increases net radiation at the surface, as well as the net radiation arrived at the ground due to the enhancing downward longwave radiation to the ground from the WGS, raising the ground temperature by up to 0.1 °C in winter. On average, ground warming reduces snow depth (up to about 6 mm) and snow cover fraction (up to about 3 %). This negative impact of WGS on snow cover seems more obvious in areas with heavier snow cover. Overall, this study highlights the feedback of changes in non-growing season vegetation cover to climate change in cold regions.