Historical and Future Changes in the Length of the Vernal Window in the Northeastern United States

Authors: Alexandra Contosta*, University of New Hampshire, Elizabeth Burakowski, University of New Hampshire, Danielle Grogan, University of New Hampshire
Topics: Environmental Science, Climatology and Meteorology, Cryosphere
Keywords: climate change, seasonal snow cover, phenology, vernal window, ecosystem function
Session Type: Paper
Day: 4/3/2019
Start / End Time: 8:00 AM / 9:40 AM
Room: Stones Throw 1 - Granite, Marriott, Lobby Level
Presentation File: No File Uploaded

The vernal window is the time between when air temperatures warm above freezing to initiate snowmelt and when forest canopies fully leaf out. The vernal window is a key period for the functioning of seasonally snow-covered, forested ecosystems that may shift in changing climate. In the Northeastern United States, winter has warmed much more rapidly than the growing season. Shorter winters could lead to a lengthening of the entire vernal window window, potentially altering energy, water, and carbon balances as ecosystems trend toward warmer and less snowy winters. Here, we explore historical and future changes in the timing and duration of the vernal window, assess biogeochemical asynchronies that occur within the window, and discuss potential impacts on forest ecosystem function. We forced the Water Balance Model (WBM) with a high resolution (4 km), 29-member ensemble of statistically downscaled temperature and precipitation data under lower and higher climate scenarios. WBM projects snowmelt dates that advanced at a faster rate than canopy closure estimated using a suite of phenology models for dominant deciduous species in the region. The most extreme case is a shift into a snow-free regime in which the vernal window ceases to exist and is replaced by a prolonged period of increased net radiation into forest ecosystems between senescence and leaf out that may fundamentally alter ecosystem function. Large uncertainties in future precipitation trends limit understanding of how future growing season climate will respond to an absence of seasonal snow cover in the Northeastern United States.

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