CR 72:53-72 (2017)  -  DOI: https://doi.org/10.3354/cr01450

ABSTRACT: Understanding the impacts of climate change on frost-free seasons is key to designing effective adaptation strategies for ecosystem management and agricultural production. This study examines the potential changes in the frost-free season length between historical (1971-2000) and future (2041-2070) periods over the contiguous USA with a focus on spatial variability and the uncertainties surrounding the projections, using daily minimum temperature outputs from a 6-member ensemble composed of 3 regional-climate models nested within 3 general‑circulation models provided by the North American Regional Climate Change Assessment Program (NARCCAP). Despite broad agreement among ensemble members on future advance (delay) of last spring (first autumn) frost and thus an increase in the frost-free season length across the USA, large inter-model spread, an indication of high uncertainties, exists especially over the mountainous West. The uncertainty surrounding the first autumn frost is the major contributor to the high uncertainty in the projected frost-free season length for the West, in contrast to other regions, especially the Great Plains, where the ensemble spread in the last spring frost contributes more to the season-length uncertainty. The lengthening is not symmetric in spring and autumn, and the asymmetry, which varies by region and model, is relatively small in the eastern and central USA, and large in the western USA. Across California and portions of the Southwest, the advance in the last spring frost will be more than the delay in the first autumn frost. Elsewhere in the western USA, especially over high terrain, the frost-free season will lengthen more in autumn than in spring.

KEY WORDS: Frost-free season · Frost dates · Growing season · Climate change impact · NARCCAP · Ensemble projection