Record early snow disappearance in 2020 and 2022 across central Svalbard

The High Arctic Archipelago of Svalbard is experiencing rapid increase in temperature due to climate warming, leading to significant changes in the characteristics of snow cover, with subsequent impacts on terrestrial ecosystems. In particular, the timing of snow disappearance is important for vegetation, permafrost dynamics and wildlife. The Sentinel-2 mission provides high resolution optical images of snow cover and represents a highly valuable tool for monitoring snow cover during the melting season, as well as interannual changes in the timing of snow disappearance. In this study, a cloud-free time-series of daily Sentinel-2 Normalized Difference Snow Index (NDSI) data from 2019 to 2023 with 20 m pixel resolution has been processed for central Spitsbergen. The dataset has been used in mapping the first snow-free day (FSFD) for each year in the time series and shows high and significant correlation with meteorological station-based measurements of FSFD. The dataset indicates that record early FSFD occurred across the study area in 2020 and 2022, corresponding to record high daily mean temperatures measured in late May during those years. Compared with a previously processed daily clear-sky MODIS NDSI based dataset for the 2000 – 2022 period, the Sentinel-2 estimates of FSFD indicates that FSFD during the years 2020 and 2022 occurred one month earlier than in 2008, when FSFD occurred late with respect to the average. Combining observations from the Sentinel-2 and MODIS NDSI based mapping, we find that there is a clear a trend towards earlier FSFD for central Svalbard. • Svalbard, located between 76°30ʹN and 80°50ʹN, is among the regions in the world with the most rapid temperature increase • Cloud-free time-series of daily Sentinel-2 data from 2019 to 2023 has been processed for central Spitsbergen • Record high daily mean temperatures in late May in 2020 and 2022 resulted in record early snow disappearance across central Svalbard those years • A clear a trend towards earlier first snow-free day for central Svalbard