Does an Early Spring Mean an Early Summer? Relationships in Intra-seasonal Growing Degree Day Thresholds Across Base Temperatures and Geography
Abstract
Anomalously early spring warmth and phenological activity typically draws a great deal of attention; for example, the particularly early spring in much of the U.S. 2017 dominated news media for weeks. Often, declarations of "early spring" are based on earlier-than-normal activity among species that initiate activity in the leading edge of the spring season. Less attention is paid to the timing of later-season plant or animal activity in years characterized by anomalously early warm temperatures. We ask, if an early-season heat-driven event happens earlier than normal, will later-season heat-driven events similarly occur earlier than normal? Being able to anticipate when later-season events are likely to occur based on early-season temperature conditions could guide a host of planning and management activities related to the start of the allergy season, harvest dates, pest and pathogen detection, invasive species management and seasonal activities focused on biological events like peak bloom.
Using high-resolution daily temperature data, we calculated the day of year three growing degree day thresholds (50GDD, 250GDD, 450GDD) were met on two base temperatures (1948-2016). We examined pixel-wise detrended correlations among all combinations of threshold anomalies over the study period. Correlations between the day of year the first two thresholds were met were low (base 0°C: 0.59±0.10) and varied by geography and base temperature. In contrast, correlations between 250GDD and 450GDD were stronger (base 0°C: 0.88±0.04). This pattern of increasing correlation strength later in the season arises from a general pattern of decreasing variability in heat accumulation as the season progresses. When variability in the timing between thresholds being met is less than the variability in timing of the first threshold, anomalies in the two thresholds are more consistent and correlations are higher. These findings indicate that anomalously early occurrence of early-season phenological events do not necessarily indicate similarly early occurrence of later-season events. However, the ability to accurately predict the timing of later-season heat-driven phenological activity increases as the season progresses, across base temperatures.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.B53C..03C
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCESDE: 0476 Plant ecology;
- BIOGEOSCIENCESDE: 0480 Remote sensing;
- BIOGEOSCIENCES