Long-Term Changes and Variability of Ecologically-Based Climate Indices along an Altitudinal Gradient on the Qinghai-Tibetan Plateau

Extreme climate events are typically defined based on the statistical distributions of climatic variables; their ecological significance is often ignored. In this study, precipitation and temperature data from 78 weather stations spanning from 1960 to 2015 on the Qinghai-Tibetan Plateau were examined. Specifically, long-term and altitudinal variability in ecologically relevant climate indices and their seasonal differences was assessed. The results show that indices of daily temperatures greater than 10 degrees C and 25 degrees C show positive annual change trends during the growing season (May to September). Indices of daily rainfall greater than 2 mm, 3 mm and 5 mm positively alternate with years both in and around the growing season (May-September, April and October). In contrast, the index of daily snowfall greater than 2 mm shows opposite annual variability. Additionally, a higher altitude significantly leads to fewer days with temperature deviations above 20 degrees C, except for in October. The three abovementioned rainfall indices present significantly positive variability with increasing altitude during the growing season. In contrast, the snow index shows similar altitudinal changes in the months surrounding the growing season. This study allows us to better cope with the threats of climate change to vulnerable ecosystems.