Changes in snow cover climatology and its elevation dependency over Romania (1961–2020)

Abstract

Study Region: Romanian territory and the Carpathian Mountains, Romania.Study focus: We provide a consistent picture of long-term changes in relevant snow cover characteristics, including phenology (timing of the snow onset and melting), snow cover duration, and frequency of snow cover and snow-free days in Romania, from 1961 to 2020, that could be relevant for understanding the regional dynamics of terrestrial water resources.New hydrological insights: The trend behaviour shows different dynamics between the elevation bands and Koeppen-Geiger climate regions of Romania, which may play a crucial role in the variability of snow water budgets and the distribution of water resources. We found systematic delays in snow onsets and earlier snow melting throughout the country. These trends are particularly prominent at mid-elevations and in the lowlands, reflecting the contribution of the intensified seasonal warming process in the last decades. We also observed widespread and significant declines in snow cover duration, snow cover day frequency, and increases in snow-free days in most climate regions of the country. The trends in snow cover parameters are elevation-dependent up to 2000 m. Above 2000 m the observed changes are visibly diminished or reversed (e.g., earlier snow onsets in the alpine areas). The long-term snow cover variability shows significant shifts in the mean of the snow cover parameters, generally clustered during the 1990 s or earlier. Relationships between the large-scale atmospheric circulation (herein expressed as NAO) and changes in seasonal temperature and precipitation have been identified.