A longer vernal window: the role of winter coldness and snowpack in driving spring transitions and lags

Historically, the transition into spring is comparatively shorter than other seasons. Something striking happens after a very cold winter or when there's been a lot of snow. Things seem to wake up all together, which is why spring seems to happen so quickly and can feel so dramatic.

Alexandra Contosta, lead author and research assistant professor at the University of New Hampshire's Earth Systems Research Center

• Shows that warmer winters with less snow have resulted in a longer lag time between spring events, and thus a more protracted vernal window
• States that climate change is altering the timing and duration of the vernal window, a period that marks the end of winter and the start of the growing season when rapid transitions in ecosystem energy, water, nutrient, and carbon dynamics take place
• Aims to establish the sequence of physical and biogeochemical transitions and lags during the vernal window period and to understand how climate change may alter them
• Synthesizes observations from a statewide sensor network in New Hampshire, USA, that concurrently monitored climate, snow, soils, and streams over a three-year period and supplemented these observations with climate reanalysis data, snow data assimilation model output, and satellite spectral data
• Finds that some of the transitions that occurred within the vernal window were sequential, with air temperatures warming prior to snow melt, which preceded forest canopy closure
• Finds that other transitions were simultaneous with one another and had zero-length lags, such as snowpack disappearance, rapid soil warming, and peak stream discharge.
• Models lags as a function of both winter coldness and snow depth, both of which are expected to decline with climate change
• Finds that warmer winters with less snow resulted in longer lags and a more protracted vernal window
• Concludes that this lengthening of individual lags and of the entire vernal window carries important consequences for the thermodynamics and biogeochemistry of ecosystems, both during the winter-to-spring transition and throughout the rest of the year