Interacting effects of temperature and precipitation on climatic sensitivity ofspring vegetation green-up in arid mountains of China

Vegetation spring phenology in arid mountain regions is undergoing profound changes as a result of recent climate anomalies. While shifts in the timing of growth onset have been widely attributed to temperature and precipitation, interacting effects of these two climate variables on phenology have not been explored. To better understand whether an interaction between temperature and precipitation may be present, and how it may affect phenology, we first determined the influence of preseason temperature and precipitation on the starting date of vegetation growing season (SOS), and then investigated the spatial pattern of climatic sensitivity of SOS and its relation to preseason temperature/precipitation. We used satellite-derived estimates of SOS for the Qilian Mountains (QLMs) in northwestern China. Our results revealed a significant interaction between temperature and precipitation, contributing up to 30% of total variability in predicted ecosystem-level SOS. This interacting effect was likely achieved through the influence on climatic sensitivity of SOS; we found a close relationship between temperature sensitivity and preseason cumulative precipitation, and a significant association between precipitation sensitivity and preseason temperatures. Spatially, SOS was more sensitive to variability in preseason temperature in wetter than in dryer areas; likewise, a spatial increase in thermal accumulation often corresponded to an enhancement in precipitation sensitivity of SOS. These findings highlight the importance of interacting effects of climatic variables in model projections of future spring phenology, and indicate that unexpected shifts in vegetation phenology in response to climatic extremes may occur under the influence of strong interactions of climatic factors.