Science Source

Evaluating changes in season length, onset, and end dates across the United States (1948–2012)

States that as climatological studies utilize temporally and spatially static definitions of seasonal definitions, the understanding of seasonal change may be limited by the way in which seasons are defined
This research serves as a challenge to this perspective by examining the changes in seasons by incorporating variability into the way in which seasons are defined
Defines temporally and spatially variable seasons were defined based on thresholds of apparent temperature and upper-level circulation patterns for the period 1948–2012
Uses two apparent air temperature metrics (and 60 US surface stations) to define seasons that vary spatially and temporally
Observes late starts of autumn and winter since 1948 and earlier onsets of spring and summer
Finds that, for the individual stations, the largest shifts occurred along coasts and in larger, more urbanized environments
Finds that individual locations also showed increased variability in start date, and significant changes were found for all four seasons in the circulation approach
States that seasons have been shown to be important for a variety of processes including phenological responses and human adaptation to extreme temperature environments; and that the consideration of season variability may be appropriate for future climatological research