The contributions of climate, permafrost, and snow factors to vegetation change in northern hemisphere permafrost regions

Northern permafrost regions are experiencing a warming trend, leading to permafrost degradation and changes in snow cover. Concurrently, vegetation is generally greening, primarily attributed to climatic factors such as air temperature. However, the contributions of permafrost (active layer thickness, ALT) and snow (earlier snow onset, SOM) to vegetation changes remain unclear. For 2001–2021, we therefore determine the start of the growing season (SOS), the end of the growing season (EOS), and the annual maximum normalized difference vegetation index (MaxNDVI) as indicators of vegetation growth. We also chose representative factors for climate, permafrost, and snow. The results indicate an earlier soil thaw start date (SOT) and a deepening of the ALT promoted the earlier SOS and the increase in MaxNDVI. SOM also facilitated the earlier SOS, while also affecting MaxNDVI. Increased snow depth positively influenced vegetation growth in some areas. From 2001 to 2021, the average contribution of climate, permafrost, and snow factors to vegetation changes ranged 61–72 %, 15–25 %, and 12–14 %, respectively. Climatic factors remained the dominant drivers of vegetation change, followed by permafrost. For SOS, SOT and ALT exhibited positive and negative influences, respectively. For EOS, changes in ALT showed a negative influence, indicating that continued deepening of ALT may hinder the delay of EOS and shorten the growing season. Snow cover had a far smaller influence on vegetation changes compared to climate. This study represents the first attempt to quantify the contributions of climate, permafrost, and snow to vegetation changes in northern permafrost regions, providing new insights and laying the groundwork for future research.