Adaptation of rice to climate change through a cultivar-based simulation: a possible cultivar shift in eastern Japan

As surface warming threatens rice production in temperate climates, the importance of cool regions is increasing. Cultivar choice is an important adaptation option for coping with cli- mate change but is generally evaluated with a single metric for a few hypothetical cultivars. Here, we evaluate adaptation to climate change based on multiple metrics and cultivars in presently cool climates in Japan. We applied the outputs of a global climate model (MIROC5) with a Repre- sentative Concentration Pathways 4.5 scenario, dynamically downscaled to a 10 km mesh for the present (1981�2000) and future (2081�2099) climate conditions. The data were input into a rice- growth model, and the performances of 10 major cultivars were compared in each mesh. With the present-day leading cultivars, the model predicted reduced low-temperature stress, a regional average yield increase of 17%, and several occurrences of high-temperature stress. The most suit- able cultivars in each grid cell changed dramatically because of climate change when a single metric was used as a criterion, and the yield advantage increased to 26%. When yield, cold, and heat stress were taken into account, however, the currently leading cultivars maintained superi- ority in 64% of the grid cells, with an average regional yield gain of 22%, suggesting a require- ment for developing new cultivars by pyramiding useful traits. A trait such as low sensitivity to temperature for phenology helps in ensuring stable growth under variable temperatures. Increas- ing photoperiod sensitivity can be an option under future climates in relatively warmer regions.