Please join EEB/EEOB for our weekly seminar series. This week's invited speaker is Dr. Julio Betancourt, Science and Decision Center, USGS, Reston, VA .
Title: Indexing the North American Spring: Patterns, Sources and Impacts of Timing Variations and Trends in Seasonal Transitions across the Coterminous U.S.
Seasonal timing has myriad impacts on plants and animals, biospheric processes, and human systems, and is critical for formulating adaptive responses to both climate variability and change. In the U.S., the timing of seasonal transitions varies widely from year to year and is also changing directionally, yet the climatic drivers, patterns, and consequences of these variations are not well understood. To better understand patterns, sources, and consequences of seasonal timing, in 2007 I helped establish the USA National Phenology Network (www.usanpn.org). NPN is a large-scale network of repeated and integrated plant and animal phenological observations, and the tools to analyze them at local to national scales. I will talk briefly about the genesis of this successful national network, and will illustrate its utility using day-of-year (DOY) metrics that define spring onset in the U.S. and their spatiotemporal variation over the last century.
In the conterminous U.S., spring onset, as defined by DOY metrics, exhibit secular trends consistent with both natural variability and greenhouse warming. Abrupt advances in spring occurred for most regions around the 1980’s and abrupt delays in fall occurred around the mid-1990s. Secular (gradual) trends in spring advance are most evident in upper Great Lakes/Midwest. Other regions are characterized by “warming holes,” with delayed spring onset abruptly ~1958 in the Southeast, advanced autumn onset in the High Plains gradually since the 1950’s, and marked decadal variability in the Pacific Northwest. In the West, both snowmelt and accumulated heat needed to bring plants out of winter dormancy track Pacific Ocean variability. In the atmosphere, spring onset variations and trends also appear linked to the Pacific North American (PNA) pattern and the Northern Annular Mode (NAM). Abrupt and broadly- synchronous springtime warming across the West after 1984 synchronized environmental changes, including snowpack depletion, across what had been a persistent N-S dipole in precipitation and snowpack during the last millennium. A deep and integrated understanding of this shift and its myriad consequences is still lacking.