No significant trends in snow free days at three long-term monitoring sites in the high-, mid- and low- Arctic Greenland as seen by MODIS Terra from 2000–2025

Abstract. Snow cover is a key component of Arctic ecosystems, regulating both biotic and abiotic processes such as plant phenology, soil thermal regimes, greenhouse gas fluxes, and the timing of glacier melt. We present a 26-year (2000–2025) record of snow-free days derived from the MODIS Terra cloud-gap-filled snow cover product at three long-term monitoring sites in high, mid, and low-Arctic Greenland. The MODIS-derived counts correlated well with in situ observations, most strongly at the high-arctic site, the only location where a direct comparison to in situ observations was possible. The mean snow-free season length is 76, 78 and 103 days at high-, mid-, and low-Arctic respectively, with a standard deviation of approximately two weeks at each site despite their contrasting latitudinal positions. We find no statistically significant trends in the number of snow-free days at any site over the record, consistent with the absence of significant trends in Northern Hemisphere snow cover in the Greenland and North American sector over the same period. The dominant driver of interannual variability shifts along the latitudinal gradient: snowfall was the dominant predictor of snow free day counts at the high arctic site, positive degree-days become co-limiting alongside snowfall at the low-Arctic site and at the mid-Arctic site positive degree-days are the only significant predictor, allthought snowfall and positive-degree-days together explain little of the interannual variance there, which point to additional physical controls. The high interannual variability in snow-free season length underscores the necessity of monitoring records spanning multiple decades in order to detect climate-change signals in snow cover and the many Arctic ecosystem processes that depend on it.