Predicted Changes in Locations Suitable for Tankan Cultivation Due to Global Warming in Japan

Researchers have predicted that most of the current satsuma mandarin-producing regions will become unfavorable for growing this citrus crop by the 2060s owing to global warming. To offer satsuma mandarin growers information for making replanting decisions, we estimated future changes in locations suitable for the cultivation of tankan (Citrus tankan Hayata), the leading subtropical citrus in Japan. The results of fruit-freezing experiments suggested that the threshold air temperature for the cold tolerance of tankan fruit is about -2°C. The locations suitable for tankan were simulated on the basis of future annual mean air temperatures evaluated by the MIROC3.2-HiRes climate model under the SRES-A1B GHG emission scenario and future annual minimum air temperatures calculated from future daily minimum temperatures evaluated by this climate model and the current air temperature variability. The results of the simulation showed that most of the Pacific coastal area from the Kanto Plain and to the west will become suitable for tankan cultivation during 2031–2050, and that coastal areas of the current satsuma mandarin-producing regions in Japan should be suitable for tankan production by 2050. The inland area of southern Kyushu Island, despite its proximity to current tankan-producing regions, is predicted to experience temperatures causing a high frequency of cold injury to tankan fruits even during 2051–2070. Therefore, if satsuma mandarin production becomes difficult on account of increased global warming, tankan could be produced as a substitute in coastal areas of the current satsuma mandarin-producing regions. However, we predict that it will be difficult to produce tankan in inland areas of the current satsuma mandarin-producing regions.