Future risk of frost on apple trees in Japan

We investigated the spring frost risk over the main apple production areas in Japan under future climates using multiple sets of global circulation models and scenarios. Frost risk was judged by the daily minimum air temperature. Apple phenology was estimated with a phenology model under future meteorological conditions. Since spring cold hardiness of apple trees depends on the phenophase, we took the effect into consideration by decomposing the season into three phenophases. April temperatures are projected to increase by 0.5–2 °C for 2031–2050 and 1.5–6 °C for 2081–2100 relative to that of 1981–2000, depending on the climate models and scenarios. Spring phenology will advance by 10 days or more for the highest temperature increase case for 2081–2100. Frost risk will not monotonically change with the future temperature increase. For the scenario with the temperature increase by 1–2 °C in spring, corresponding to the medium temperature increase case among our simulation cases, frost risk will be maximized in the southern Tohoku region and central highlands, where frost risk is relatively high under the current climates. Frost risk will tend to decrease for the highest temperature increase case. During bud break to foliation, apple trees will be in highest frost risk under future climates.