Shifting Spatial and Temporal Patterns in the Onset of Seasonally Snow-Dominated Conditions in the Northern Hemisphere, 1972–2017

Abstract

ABSTRACTThe potential for anthropogenic climate change to impact patterns of seasonal snow cover has motivated numerous studies seeking trends in its extent and duration. Many have been based on the NOAA-Rutgers record of Northern Hemisphere snow cover. Several studies have found augmented early-season snow identified from this archive to be anomalous, and related it to the introduction of higher-resolution imagery and a more automated interpretation process in 1999. This study contributes to the discussion by describing in greater detail the spatial and temporal distributions of trends in the onset of seasonally snow-dominated conditions between 1972 and 2017, and relationships to their physiographic and climatological contexts. It also identifies changepoints between negative and positive onset-date anomalies, and relates these to corresponding meteorological patterns. Most trends identified indicated earlier onset, and were associated with midlatitudes, low to moderate elevations, and colder, drier climates. These were situated largely northeast of major topographic chains, southwest of increasingly ice-free Arctic waters, and to the east of areas associated with blocking systems. Onset-date anomalies switched from positive to negative in approximately 70% of the affected points before 1997. These changepoints generally occurred earlier at higher elevations to the south and west, and later at lower elevations to the north and east. Overall temporal trajectories correspond broadly to shifts in temperature and precipitation over the same areas. In contrast, positive (later) onset trends were found over much smaller areas, associated with warmer, wetter climates and higher elevations, particularly on west-facing slopes; temporal variations in anomalies of their onset dates and associated meteorological conditions were distinct from those having negative trends.