Spatially explicit forecasting of frost damage in German apple cultivation under changing climatic conditions

Late spring frosts repeatedly cause significant yield reductions and economic losses for apple producers. Observations from recent decades show a trend toward earlier apple flowering and an increasing risk of frost damage in Germany. This raises the question of how frost risk will develop in the future. To address this question, we used weather data and crowd-sourced phenological observations from 1993 to 2022 to train the phenology prediction model PhenoFlex. Based on predicted phenological stages and critical temperature thresholds, we estimated the probability of frost damage for the future periods 2050 and 2085 under four climate scenarios (SSP1–2.6, SSP2–4.5, SSP3–7.0 and SSP5–8.5). For the timing of phenological stages preceding bloom, we estimated stage-specific shares of the trees’ heat requirements that had to be fulfilled. We assessed the probability of frost damage at 3350 locations across Germany and interpolated the results to produce frost damage risk maps for Germany. The forecast results indicate that the trend toward earlier apple blossom will continue across all climate scenarios. However, we detected regional differences in the effect on frost risk around mid-century. Toward the end of the century, the probability of frost damage decreases in most locations compared to 1993–2022, with greater reductions under more severe climate scenarios. Despite these changes, late spring frost will remain a challenge for apple production in Germany throughout the 21st century. The maps we generated can assist farmers in deciding on investments in frost protection measures, and they can provide information to policy-makers aiming to develop support measures for the fruit sector.