Fingerprints of Anthropogenic Influences on Vegetation Change Over the Tibetan Plateau From an Ecohydrological Diagnosis

Vegetation cover exerts a strong control on land-atmosphere interactions. To quantify the relative effects of external forcing (climate change) versus internal forcing (anthropogenic activity) on recent vegetation change over the Tibetan Plateau (TP), we apply an ecohydrological diagnostic framework, developed from earlier work. We compare vegetation change during 1986-2015 based on NDVI (Normalized Difference Vegetation Index) data with changes in environmental conditions (European Centre for Medium-Range Weather Forecasts Reanalysis 5th generation, ERA5). Results show that external forcing is the dominant factor behind significant vegetation change over the southeastern TP during 1986-2015. In the area with significant vegetation changing, 60.5%/41.5% of pixels have experienced a respective wetting/drying of climate, which in turn has supported greening/browning during 1986-2005/1996-2015. However, during the greening/browning transition in the latter period, the proportion of internal forcing on browning increased from 5.62% to 19.4%, indicating that anthropogenic factors are playing an increasingly role on impacting vegetation change in recent decades. Plain Language Summary In climate systems, vegetation is a layer that is situated at the border of the atmosphere and land surface, controlling the exchange of water and energy. However, vegetation is fragile in cold and arid region like the Tibetan Plateau and can easily be influenced both by climate change (sunlight, rainfall, temperature, etc.) and by human activities (land use, grazing, farming, etc.). In order to figure out to what extent the vegetation is affected by climate change or human activities, we combine historical land surface climate data and satellite-observed vegetation data to investigate the theoretical inducement of climate and human factors. Results show that in the areas with significant vegetation changing (mostly southeastern Tibetan plateau), climate change is the dominant control of vegetation change in the past three decades. However, the human factor has significantly increased in importance over recent decades.