Effects of Snow Cover on Spring Vegetation Phenology Vary With Temperature Gradient Across the Pan-Arctic

Extensive and complex changes in spring vegetation phenology have occurred in the Pan-Arctic over the last several decades. However, the role of snow cover at the start of the growing season (SOS) under different climatic conditions remains unclear. Therefore, we compare the effects of four snow indicators on SOS from 1982 to 2015 based on long-term remote sensing data and found that snow cover end date (SCED) is the main snow indicator affecting SOS, with SOS advancing 0.56 days for each 1-day advance in SCED, explaining 12%-90% of SOS variability in 63% of the Pan-Arctic region. The results also demonstrate that SCED is the dominant factor on SOS in 13% of the Pan-Arctic region and the effects of SCED on SOS vary with temperature gradient rather than precipitation gradient. In cold areas, the positive effect of SCED on SOS diminished with increasing temperature, while in warm areas, the positive effect of SCED on SOS increased with increasing temperature. As the climate warms, the impact of SCED on SOS is expected to weaken in cold areas and increase in warm areas. The findings have crucial implications for understanding future vegetation phenological responses to climate change across the Pan-Arctic.The Pan-Arctic is undergoing dramatic environmental changes. Changes in spring vegetation phenology, one of the most critical climate-induced changes, have not always followed the global advancement trends. The role of changing snow cover in a considerable amount of variation in spring vegetation phenology under various climatic conditions is still not clear. Based on long-term remote sensing datasets, we find that snow cover influenced 63% of Pan-Arctic terrestrial spring vegetation phenology, with a 1-day advance in snowmelt followed by a 0.56-day advance in spring vegetation phenology. The effect of snowmelt on spring vegetation phenology varies by area and is related to the temperature rather than precipitation. There are different modes of the impact of snowmelt on spring vegetation phenology in cold and warm areas. The impact of early snowmelt on spring vegetation phenology is expected to diminish in cold areas and increase in warm areas as the climate warms across the Pan-Arctic. Our results contribute to a better understanding of the future vegetation status of the Pan-Arctic ecosystem in the context of climate change.