Spatiotemporal variability of false spring events in the temperate and boreal regions

Abstract

False spring, defined as frost events occurring after vegetation growing season has begun, can lead to severe ecological and economic damage in temperate and boreal regions. While global warming generally advances the start of the growing season and extends its duration, it can paradoxically increase the risk of frost damage to vegetation during its accelerated growth stages. Here we show the spatiotemporal patterns of false spring events and identify their climatic drivers across the northern temperate and boreal regions (30- 70°N), in the period from 1950 to 2022. We examine key metrics including the number of false spring (FS) days, the start of the growing season (SOS), the last spring frost date (LSF), and the growing degree days accumulated up to LSF (GDDLSF) using observation-based temperature datasets. The results indicate that the number of FS days has increased across most regions during the recent period, despite a general decrease in overall frost days. Significant increases in FS events are notably evident in Europe, central North America, and Siberia. This increase is primarily driven by SOS advancing faster than LSF, thereby extending the exposure period during which vegetation is vulnerable to frost. Furthermore, larger GDD changes accumulated until the LSF date in many regions imply greater vulnerability, as vegetation in more developed stages is more susceptible to freezing temperatures. Accordingly, the risk of false spring can be further intensified not only by its hazard (frequency), but also by greater vulnerability (GDDLSF) and extended exposure (LSF-SOS interval). These findings enhance the fundamental understanding of the variability and drivers of false spring events. Moreover, we underscore the need for region-specific future research, as well as adaptation and mitigation strategies for both agricultural systems and natural vegetation.