Science Source

Observed changes in false springs over the contiguous United States

States that advances in green-up timing may leave early stage vegetation growth vulnerable to cold damage when hard freezes follow green-up resulting in a false spring
Examines spatiotemporal patterns of green-up dates, last spring freezes, and false springs across the contiguous United States from 1920 to 2013
Analyzes observational record of 882 stations from the United States Historical Climatology Network
Results indicate widespread earlier green-up and last spring freeze dates over the period
Finds the contiguous U.S. saw widespread earlier green up (GU) and last spring freeze (LSF) dates from 1920 to 2013
Finds the LSF date advanced on average by 5.8 days over the record compared to an average advance by 1.8 days for GU date
Finds that truncating the period from 1950 to 2013 results in an average advance in GU and LSF dates by 4.2 and 7.9 days
States this asynchronous advance in LSF dates relative to GU is hypothesized to decrease potential for cold damage or mortality
Finds that, although regionally variable, these changes resulted in a reduction in false springs, notably over the past 20 years, except across the intermountain western United States where the advance in green-up timing outpaced that of the last spring freeze
A sensitivity experiment shows that observed decreases in false springs are consistent with a warming climate