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Observed changes in false springs over the contiguous United States



Climate warming fosters an earlier spring green-up that may bring potential benefits to agricultural systems. However, 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. Spatiotemporal patterns of green-up dates, last spring freezes, and false springs were examined across the contiguous United States from 1920 to 2013. Results indicate widespread earlier green-up and last spring freeze dates over the period. Observed changes in these dates were asymmetric with the last spring freeze date advancing to earlier in the year relative to green-up date. 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.

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