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Abstract. Rapid climate warming speeds up the solid-liquid water cycle and reduces the solid water storage in cold regions of the Earth. Snowfall is the most crucial input for the cryosphere. However, the potential snowfall phenology (PSP) variability has not been systematically and comprehensively studied. For this reason, we initially proposed three indicators, i.e., the start of potential snowfall season (SPSS), the end of potential snowfall season (EPSS), and the length of potential snowfall season (LPSS), to describe the characteristics of the PSP, then we explored the spatial-temporal variation of those three PSP indicators past, present, and future across the Chinese Tianshan mountainous region (CTMR) based on the observed daily air temperature from 26 meteorological stations during 1961–2017/2020 combined with 14 models data from CMIP6 (the Phase 6 of the Coupled Model Intercomparison Project) under four different scenarios (SSP126, SSP245, SSP370, and SSP585) during 2021–2100. It proved that the SPSS, EPSS, and LPSS could reproduce features of the PSP well across the study area. In the past and present, the potential snowfall season started on October 29th, ended on March 20th, and lasted for about four months and 23 days across the CTMR on average. The rate of advancing EPSS (−1.6 days/10a) was faster than that of postponing SPSS (1.1 days/10a) during 1961–2017/2020. It also found significant delaying by 2–13 days in the starting time, and advancing for 1–13 days in the ending time, respectively, which reduced 1–27 days for the LPSS. The potential snowfall season started later, ended later, and lasted longer in the north and center than in the south. Similar to the past and present, the SPSS, EPSS, and LPSS will vary under four emission scenarios during 2021–2100. Potential snowfall season will start later, end earlier, and last fewer days under the higher emission scenario. Under the highest emission scenario, SSP585, the starting time will be postponed by 41 days in 2100, while the ending time will be up to 23 days in advance in 2100, implying that it will cut down the length by 63 days (about two months), and the length of the potential snowfall season will only last two and a half months in 2100 under the SSP585 scenario. Spatially, the length of the potential snowfall season in the west and southwest of the CTMR will be compressed by more days because of the more delayed starting time and advanced ending time under all four scenarios. The results indicate that annual total snowfall will decrease, including amount and frequency, then reduce snow cover or mass, which finally feedback to the atmosphere in the form of more rapid warming for the lower reflectivity to solar radiation. Our research provides a new direction to capture the potential snowfall phenology in the alpine region and can be easily expanded to other snow-dominated areas worldwide.

Abstract. The acceleration of climate warming has led to a faster solid–liquid water cycle and a decrease in solid water storage in cold regions of the Earth. Although snowfall is the most critical input for the cryosphere, the phenology of snowfall, or potential snowfall phenology (PSP), has not been thoroughly studied, and there is a lack of indicators for PSP. For this reason, we have proposed three innovative indicators, namely, the start of potential snowfall season (SPSS), the end of potential snowfall season (EPSS), and the length of potential snowfall season (LPSS), to characterize the PSP. We then explored the spatial–temporal variation in all three PSP indicators in the past, present, and future across the Chinese Tianshan mountainous region (CTMR) based on the observed daily air temperature from 26 meteorological stations during 1961–2017/2020 combined with data from 14 models from CMIP6 (Phase 6 of the Coupled Model Intercomparison Project) under four different scenarios (SSP126, SSP245, SSP370, and SSP585, where SSP represents Shared Socioeconomic Pathway) during 2021–2100. The study showed that the SPSS, EPSS, and LPSS indicators could accurately describe the PSP characteristics across the study area. In the past and present, the potential snowfall season started on 2 November, ended on 18 March, and lasted for about 4.5 months across the CTMR on average. During 1961–2017/2020, the rate of advancing the EPSS (−1.6 d per decade) was faster than that of postponing the SPSS (1.2 d per decade). It was also found that there was a significant delay in the starting time (2–13 d) and advancement in the ending time (1–13 d), respectively, resulting in a reduction of 3–26 d for the LPSS. The potential snowfall season started earlier, ended later, and lasted longer in the north and center compared with the south. Similarly, the SPSS, EPSS, and LPSS indicators are also expected to vary under the four emission scenarios during 2021–2100. Under the highest emission scenario, SSP585, the starting time is expected to be postponed by up to 41 d, while the ending time is expected to be advanced by up to 23 d across the study area. This change is expected to reduce the length of the potential snowfall season by up to 61 d (about 2 months), and the length of the potential snowfall season will only last 2.5 months in the 2100s under the SSP585 scenario. The length of the potential snowfall season in the west and southwest of the CTMR will be compressed by more days due to a more delayed starting time and an advanced ending time under all four scenarios. This suggests that, with constant snowfall intensity, annual total snowfall may decrease, including the amount and frequency, leading to a reduction in snow cover or mass, which will ultimately contribute to more rapid warming through the lower reflectivity to solar radiation. This research provides new insights into capturing the potential snowfall phenology in the alpine region and can be easily extended to other snow-dominated areas worldwide. It can also help inform snowfall monitoring and early warning for solid water resources.