Ground observed climatology and trend in snow cover phenology across China with consideration of snow-free breaks

Abstract

Accurate understanding of snow cover phenology and its changes is important to hydrological processes and climate system. Having recognized the potential uncertainties in remote sensing snow cover products, we used daily snow depth observations from 514 meteorological stations across China to investigate the spatiotemporal variations in snow cover phenology during 1970–2014. Climatologically, the snow cover onset date (Do) and end date (De) as well as the number of snow cover days (Ds) depended on latitude at most stations outside of the Tibetan Plateau (TP). For the high-elevation stations, which were mainly in the TP, multiple snow-free breaks (SFBs) during the cold season made Ds insensitive to Do and De. Furthermore, the number of SFBs (Db) increased significantly with the rise in elevation, explaining why higher altitudes in TP did not necessarily have greater Ds values despite the earlier Do and later De values. From 1970 to 2014, most stations in China exhibited delayed Do and advanced De due mainly to the increased temperature, but such trends were significant at only 10.5% and 15.4% of the stations, respectively. During the same period, shortened Ds primarily occurred south of ~ 40° N, whereas the opposite ones dominated north of ~ 40° N. Most stations (except those in Hexi Corridor) with significant growth in Ds were characterized by delayed Do and advanced De. Such a phenomenon of “increased snow cover days during shortened cold season” was due to the significant shrinkage in Db values. The spatial pattern of the trends in annual total snow depth overall follows that of Ds, suggesting that the Ds, when takes SFBs into consideration, could be an indicator of variations of snow water resources in China. The trends in Do, De and Ds were not elevation dependent in TP.