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 20years, 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. Key Points <list list-type="bulleted" id="grl51508-list-0001"> <list-item id="grl51508-li-0001">Last spring freeze timing advanced relative to green-up across contiguous U.S. <list-item id="grl51508-li-0002">False springs generally decreased as result of asymmetric changes <list-item id="grl51508-li-0003">Sensitivity analysis supports false spring changes consistent with warming