Snowmelt control on spring hydrology declines as the vernal window lengthens

The vernal window, or the winter-to-spring transition, is a key period for seasonally snow-covered, forested ecosystems. The events that open and close the vernal window shape the unique characteristics of spring hydrology that, in turn, influence both terrestrial and aquatic ecosystem processes. Few studies have examined how climate change will alter the vernal window and thereby impact basic hydrology during this transitional period. We project that over the 21st century the vernal window will lengthen by +15 to +28 d in northeastern North America. Loss of snow cover under a high climate forcing scenario eliminates the vernal window across 59% of the study domain, removing snow's influence on spring runoff in those areas. Spring runoff timing where the vernal window lengthens but does not disappear becomes similar to the southern, snow-free region where precipitation drives winter runoff, indicating a fundamental change in the hydrologic character of northeastern forests.