Evaluating late spring frost risks of apple in the Loess Plateau of China under future climate change with phenological modeling approach

Abstract

Changes in apple phenology associated with climate change have attracted extensive attention. However, it is poorly known whether the phenological dynamics responding to climate change would increase the severity and frequency of frost in apple trees. Here, we investigated the variation of phenophase (budburst and fruit-setting) and the frost risk for apple trees in the Loess Plateau combined with phenology models driven by Global Climate Models (GCMs) under two emission scenarios (SSP2-RCP4.5 and SSP5-RCP8.5 for two time periods 2050s and 2090s, respectively). The results showed that apple budburst and fruit-setting are expected to be advanced to varying degrees, but the rate of advance is decreasing (budburst 0.04–0.14 d∙y−1, fruit-setting 0.12–0.22 d∙y−1). The combinations of high emission scenarios and ‘far’ time periods (SSP5-RCP8.5, 2090s) in budburst and fruit-setting advance larger than conservative emission scenarios and ‘near’ time periods (SSP2-RCP4.5, 2050s). Furthermore, although frost frequency is expected to decrease about 0.09–0.36 d under both SSP2-RCP4.5 and SSP5-RCP8.5, frost intensity tends to increase about 0.004–0.008 °C·d−1 (except SSP5-RCP8.5, 2090s). Due to the different directions of changes in frequency and intensity of frost under future time periods, overall frost risk showed regional differences. The unchanged or decreased frost risk distributed in the northern and southern areas of the study areas, while the increased frost risk mainly distributed across the central areas of the study areas. Finally, the advancement of two phenophase was disproportionately related to frost risks in the geographic distributions. Areas with large advance in phenophase were themselves expected to be at greater frost risk. Our findings will help to promote local preventative interventions for reasonably reducing the risk of late spring frosts in future climate warming scenarios.