Snow cover variability in Bulgarian mountainous regions, 1931–2000

Abstract

AbstractPrincipal component (PC) analysis was carried out on annual snow cover series from 15 mountain climate stations in Bulgaria to characterize the spatial and temporal variability in snow cover over the 1931–2000 period. Three distinct snow cover response regions were identified: (1) high elevation sites above 1500 m in the Vitosha and Rila Mountains; (2) low elevation sites below 1000 m in the eastern Rhodope and southern Pirin Mountains and (3) a mid‐mountain zone of 1000–1500 m elevation including stations from several mountain ranges. Snow cover exhibited evidence of significant decadal‐scale variability over the 1931–2000 period but little evidence of long‐term trends linked to climate warming. Over the more recent 1971–2000 period, the mid‐mountain zone has increased in importance and shows a significant trend toward a later start to the snow cover season.Composite analysis of high and low snow accumulation winters showed high accumulation years associated with a negative North Atlantic Oscillation (NAO)/East Atlantic (EA)‐like pattern that favored increased winter precipitation over the Mediterranean and Balkans and anomalous easterly flow across the Black Sea into Bulgaria. Low snow accumulation years were associated with the positive mode of a Scandinavian (SCA)‐like pattern that generated fall warming, a delay to the start of the snow cover season and reduced winter precipitation. Correlation of annual snow cover series with these modes of atmospheric variability revealed few significant correlations but evidence of considerable secular variability in the strength and sign of the relationships. This reflects the complex climate regime of Bulgaria, which is located at the cross‐roads of Mediterranean and Continental climate influences and on the periphery of the main nodes of influence of Northern Hemisphere circulation patterns that play important roles in European snow cover variability. Copyright © 2007 Royal Meteorological Society