Biologically-Relevant Trends in Springtime Temperatures Across the United States

Research output: Contribution to journalArticle

Abstract

Long-term trends in temperature—a primary driver of phenology—are typically evaluated using monthly or seasonal averages. However, accumulated warmth, rather than average temperature, cues phenological events; further, the amount of heat necessary to trigger activity is species-specific. We evaluated trends in the timing of three heat accumulation thresholds encompassing spring-season biological activity in the conterminous United States over a 70-year period to document changes from a biologically relevant perspective. The Southwest, Northeast, and Northwest regions exhibit the strongest advancements. Rates of change vary among thresholds within many regions, resulting in temporal compression and lengthening within the season. Further, in the Eastern United States, the days between when a single threshold is met in the south and north are decreasing; in the West, the opposite pattern is occurring. These trends generally match long-term observations of species' phenology, underscoring the value of this approach for documenting biologically relevant changes in temperature.

Original languageEnglish (US)
Pages (from-to)12377-12387
Number of pages11
JournalGeophysical Research Letters
Volume46
Issue number21
DOIs
StatePublished - Nov 16 2019

Keywords

  • growing degree days
  • phenology
  • spring season
  • thresholds
  • trends

ASJC Scopus subject areas

  • Geophysics
  • Earth and Planetary Sciences(all)

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