Abstract
It is predicted that climate change will make the cultivation of satsuma mandarins more challenging unless adaptation measures can be implemented in current production areas, although changing conditions may favor the cultivation of subtropical fruit trees such as avocado. Therefore, we assessed suitable locations for the future cultivation of both tree species in Japan and the potential of avocado as a substitute for satsuma mandarin. Suitable locations were determined using the annual mean (satsuma mandarin) and minimum (both species) temperatures calculated from the projected temperatures based on two global climate models (MRI-ESM2-0 and MIROC6) under three shared socioeconomic pathways (SSP). Suitable locations for satsuma mandarins were predicted to move northward until the mid-21st century under SSP1-RCP2.6 or until the end of the 21st century under SSP2-RCP4.5 and SSP5-RCP8.5. Among the suitable locations for satsuma mandarins for 1990-2009, the percentage that remained suitable for 2080-2099 varied depending on the SSP, ranging from 0% (SSP5-RCP8.5) to approximately 80% (SSP1-RCP2.6). This highlights the substantial impact of climate change mitigation measures on current satsuma mandarin production areas. Suitable locations for avocados were projected to certainly expand definitely in the future, regardless of the SSP, and many of the suitable locations for satsuma mandarins for 1990-2009 will become suitable for avocados for 2040-2059. Because temperature conditions are suitable for avocado cultivation in most locations that will become too warm for satsuma mandarin production in the future among the suitable locations for satsuma mandarin for 1990-2009, replanting from satsuma mandarins to avocados is an adaptation option in current production areas. Although adaptation measures using cultivation techniques and high-temperature-tolerant cultivars are likely to become less effective as climate change progresses, replanting to avocados was shown to be an effective alternative, at least until the end of the 21st century.
1. Introduction
Climate change has exacerbated the adverse effects of high temperatures on the most widely cultivated fruit tree in Japan, satsuma mandarins, such as causing puffy fruits (Sato and Ikoma, 2020) and physiological fruit drop (Sato et al., 2010), while reducing cold damage (Sugiura et al., 2012, 2007). It is anticipated that adaptation measures will be necessary to continue satsuma mandarin cultivation in the current production areas owing to the predicted northward shift of suitable cultivation locations in the future (Sugiura and Yokozawa, 2004). Conversely, climate change is expected to intensify in areas where subtropical fruit trees can be cultivated in open fields and unheated plastic greenhouses, which may lead to an increase in the domestic production of these crops (MAFF, 2020a), which can also serve as a substitute crop for satsuma mandarin.
The current production of avocados, a subtropical fruit, is 22 t in Japan, while imports amount to 62,000 t (MAFF, 2024). As the high domestic demand necessitates a high volume of avocado imports, stable sales can be expected, even with the expansion of domestic avocado production (Kisaki et al., 2024). Cultivating avocados domestically allows them to ripen fully on the tree, resulting in higher-quality fruits than imports (Kondo and Honsho, 2018). In this study, we estimated the distribution and suitable locations for future avocado cultivation in Japan. Additionally, the vulnerability of satsuma mandarin production to climate change and the potential of avocado as a substitute crop for satsuma mandarins were assessed.
2. Materials and Methods
Suitable locations for satsuma mandarin (Citrus unshiu Marcow.) or avocado (Persea americana Mill.) cultivation in Japan were determined using 20 years of temperature data (1990-2009, baseline period; 2040-2059, mid-21st century; 2080-2099, late 21st century) for each 1-km grid in the country (each grid cell is 45” longitude × 30” latitude). The temperature data used and the criteria for determining suitable locations were as follows:
2.1 Temperature data
As the observed air temperature for the baseline period, we used the daily mean and minimum temperatures for 1990-2009 in the Agro-Meteorological Grid Square Data (Ohno et al., 2016), a climate dataset with a 1-km resolution covering the period from 1980. Projected air temperatures in the middle or late 21st century were calculated from 20 years (2040-2059 or 2080-2099) in the Bias Corrected Climate Scenarios over Japan Based on the CDFDM Method Using CMIP6 (Ishizaki, 2021), a climate dataset with 1-km resolution covering 1900-2100. This dataset was developed using climate scenarios derived from five global climate models (GCMs) under three shared socioeconomic pathways (SSPs) and utilized daily observational data (the Agro-Meteorological Grid Square Data) for the reference period (1980-2018) for bias correction. We used the monthly mean temperature (TMmean) and monthly mean daily minimum temperature (TMmin) derived from two GCMs (MRI-ESM2-0 and MIROC6; hereafter “MRI” and “MIROC”) simulated for SSP1-RCP2.6, SSP2-RCP4.5, and SSP5-RCP8.5 (hereafter “SSP126”, “SSP245”, and “SSP585”). Each of the three SSPs corresponds to a low, intermediate, or very high greenhouse gas emissions scenario (IPCC, 2021).
The mean increase in TMmean for 2040-2059 relative to 1990-2009 was calculated as the difference between the 20-year TMmean means for these two periods. The projected daily mean air temperatures from 2040-2059 were calculated as the sum of the observed daily mean temperatures from 1990-2009 and the mean increase in TMmean for 2040-2059. The projected daily minimum air temperatures from 2040-2059 were calculated as the sum of the observed daily minimum air temperatures from 1990-2009 and the mean increase in TMmin for 2040-2059. Similarly, the projected daily mean and minimum air temperatures from 2080-2099 were calculated.
2.2 Criteria for determining suitable locations
The suitability of each grid for satsuma mandarin cultivation was determined according to the recommended natural conditions for the cultivation of fruit tree species in Japan (MAFF, 2020b) using the following equations:
15°C ≤ Tmean ≤ 18°C
-5°C ≤ Tmin
where Tmean and Tmin are the annual mean temperature and annual minimum temperature (lowest daily minimum temperature of the year), respectively, for each grid. Tmean was calculated from the 20-year mean of the daily mean air temperatures. For Tmin, the fifth-lowest annual minimum temperature in 20 years was used, because one of the recommended natural conditions for satsuma mandarin cultivation is that annual minimum temperatures <-5°C should only occur twice or less in 10 years (four times or less in 20 years).
As a first step, the suitability of Tmean was assessed, after which the suitability of Tmin was assessed for the grids for which Tmean was suitable. Grids for which both Tmean and Tmin were suitable were determined to be suitable locations; grids with Tmean < 15°C or Tmin < -3°C were determined to be colder than suitable locations (henceforth, “colder locations”), and grids with Tmean > 18°C were determined to be warmer than suitable locations (henceforth, “warmer locations”).
A previous study (Sugiura and Yokozawa, 2004) assessed suitable locations for satsuma mandarins based solely on Tmean. However, a study on the evaluation of suitable locations for tankans (Sugiura et al., 2014), a citrus plant grown in warmer climates, found that when assessed by the recommended natural conditions for tankans (MAFF, 2020b), there are many areas where Tmin is lower than the criteria, even though Tmean is suitable. Although fruit harvesting is possible in these areas, trees are likely to suffer cold damage during the winter. Therefore, in the present study, Tmin was included in the assessment of suitable locations for satsuma mandarins. Although satsuma mandarin yields are reduced by defoliation caused by cold damage (Konakahara, 1984), this damage is relatively minor. Therefore, sites where the annual minimum temperature falls below -5°C twice a decade are also considered suitable in the recommended natural conditions for satsuma mandarin.
Avocados can be widely grown in warm climates, where annual mean temperatures of 15-30°C are suitable for cultivation (Grüter et al., 2022). Among all grids based on all GCMs and SSPs, the highest Tmean for 2080-2099 was 27.6°C. This indicates that Tmean in all suitable locations for satsuma mandarins and in locations warmer than suitable fall within the range of Tmean in locations suitable for avocados. Therefore, in the present study, only the annual minimum temperature was used to assess the locations suitable for avocado cultivation. Avocados vary widely in cold tolerance, depending on the cultivar (Shimada et al., 2022). The “Bacon” avocado is the main cultivar grown in Japan owing to its superior quality (Kisaki et al., 2024). Kisaki et al. (2024) concluded that based on both the cold tolerance and the difference between leaf temperature and air temperature at the time of cold damage, damage to leaves and flower buds of “Bacon” avocado is most likely to occur when the daily minimum temperature is < -3°C. Thus, the following equation was used to determine suitable locations for avocado cultivation:
-3°C ≤ Tmin
The impact of cold damage on avocado yield is more severe than that on satsuma mandarins because not only leaves but also flower buds and spikes are damaged (Inoue and Takahashi, 1990; Uchino et al., 2019). In present study, locations where an annual minimum temperature < -3°C occurs once or less in 10 years (twice or less in 20 years) were considered to be suitable locations; thus, the third-lowest annual mean temperature in 20 years was used as Tmin.
3. Results
3.1 Satsuma mandarins
For 1990-2009, locations suitable for satsuma mandarin cultivation were distributed in the coastal areas of Kyushu Island and in the coastal areas on the Pacific side in and to the west of the southern Kanto Plain (Fig. 1a), covering almost all the current main production areas of satsuma mandarin. The suitable areas gradually moved northward based on the MRI under SSP245 (Fig. 1c, f). For 2040-2059, suitable locations were also distributed in some coastal areas on the Sea of Japan side, whereas warmer locations were distributed in several areas, including southern Kyushu Island. For 2080-2099, warmer locations were widely distributed over the coastal areas on the Pacific side in and to the west of the southern Kanto Plain. The warmer locations under SSP585 were wider than those under SSP245 (Fig. 1d, g). Under SSP126, some areas, such as southern Kyushu Island, appeared to be warmer locations for 2040-2059 (Fig. 1b), but there were no notable changes thereafter (Fig. 1e). Based on MIROC, the speed of the northward movement of suitable locations was slightly slower than that based on MRI, although the difference between them was slight (Fig. S1).
3.2 Avocados
For 1990-2009, suitable locations for avocado cultivation were distributed on islands around and south of Kyushu Island and in some narrow areas on the Pacific side in and to the west of the southern Kanto Plain (Fig. 2a). Based on the MRI under SSP245, suitable locations gradually expanded northward, and many of the suitable locations for satsuma mandarins for 1990-2009 became suitable for avocado for 2040-2059 (Fig. 2c). Suitable locations also expanded into some coastal areas on the Sea of Japan side for 2080-2099 (Fig. 2f). The suitable locations under SSP585 were wider than under SSP245 and were distributed in some coastal areas on the Sea of Japan side in 2040-2059 (Fig. 2d). Under SSP126, many of the suitable locations for satsuma mandarins for 1990-2009 became suitable for avocado for 2040-2059 (Fig. 2b). The total area of the suitable locations for avocado was 2.5-3.7 times larger for 2040-2059 and 2.4-7.7 times larger for 2080-2099 than for 1990-2009 (Fig. 3). Based on MIROC, the speed of the northward expansion of suitable locations was slightly slower than that based on MRI, but the difference between them was only slight (Fig. S2).
3.3 The relationship between satsuma mandarin and avocado
Approximately 20% of the suitable locations for satsuma mandarins overlapped with suitable locations for avocados for 1990-2009 (Fig. 4). Approximately 70% of the suitable locations for satsuma mandarins for 1990-2009 remained suitable for them for 2040-2059 under SSP126 and SSP245, and approximately 40% remained suitable under SSP585. Of the suitable locations for satsuma mandarins for 1990-2009, approximately 70% were still suitable for them for 2080-2099 under SSP126 and approximately 30% under SSP245. However, there were no suitable locations under SSP585. Regardless of the period or SSP, most of the locations determined to be warmer than suitable for satsuma mandarins among the suitable locations for satsuma mandarins for 1990-2009 were suitable locations for avocado.
4. Discussion
4.1 Satsuma mandarins
Suitable locations for satsuma mandarins were predicted to move northward until the mid-21st century under SSP126 or until the end of the 21st century under SSP245 and SSP585 (Fig. 1). For 2040-2059, warmer than suitable locations for satsuma mandarins were estimated to be more widespread in SSP585 than in SSP245 or SSP126 (Fig. 1 b, c, d). The mean values of Tmean for all grids were 10.7°C for 1990-2009 and 13.0°C, 12.5°C, and 12.3°C based on MRI under SSP585, SSP245, and SSP126, respectively, for 2040-2059. Although the difference in Tmean between SSP585 and SSP245 was only 0.5°C, the difference on the map was clearly evident.
In a previous study that simulated suitable locations for satsuma mandarins (Sugiura and Yokozawa, 2004), the IS92a scenario reviewed in the IPCC Second Assessment Report (IPCC, 1996) was used as the greenhouse gas emission scenario, resulting in the use of temperatures close to those under SSP585 in the present study. Consequently, the speed of the northward movement of suitable locations around the mid-21st century in a previous report is similar to that under SSP585 in the present study.
Among the suitable locations for satsuma mandarins for the baseline period (1990-2009), the percentage that remained suitable around the late 21st century varied significantly depending on the SSP, ranging from 0% to approximately 80% (Fig. 4). This highlights the substantial impact of climate change mitigation measures on current satsuma mandarin production areas.
4.2 Avocados
It is certain that suitable locations for avocados will expand in the future, regardless of SSP (Fig. 3). Many of the suitable locations for satsuma mandarins for the baseline period will become suitable for avocados around the mid-21st century (Figs 2 and Fig. 4). If the number of locations suitable for avocado cultivation increases, then domestic production can also increase. Because avocados can be produced in most locations that will become warmer than suitable for satsuma mandarin in the future, among the suitable locations for the baseline period (Fig. 4), replanting from satsuma mandarin to avocado is an adaptation option in current satsuma mandarin production areas. Measures using cultivation techniques (Sato et al., 2015) and high-temperature-tolerant cultivars (Sugiura, 2019) have been developed for producers to adapt when satsuma mandarins become difficult to grow owing to climate change. Although these adaptation measures are likely to become less effective as climate change progresses, replanting with avocados will be an effective strategy until the end of the 21st century.
Our study had several limitations. First, the criteria for suitable locations (-3°C ≤ Tmin) were determined based on the cold tolerance of leaves and flower buds of “Bacon” avocado. The cold tolerance of flowers and young fruits may be lower than that of flower buds, although air temperatures during the flower and young fruit stages are higher than at the flower bud stage. Young “Bacon” trees die at air temperatures < -4.5°C (Konno and Sugiura, 2024). Although the cold tolerance of mature trees is higher than that of young trees, the death of mature trees has a significant impact on subsequent fruit production. Climatic factors other than temperature, such as precipitation, may also be limiting factors. Additional research of the conditions required to assess suitable locations more accurately is necessary. Cultivars with higher cold tolerance than “Bacon” could potentially be grown over a wider area in Japan, so research on suitable locations for different cultivars is also needed.
Acknowledgements
This work was supported by the Environment Research and Technology Development Fund (JPMEERF20S11806) of the Environmental Restoration and Conservation Agency of Japan, and JSPS KAKENHI Grant Number 23K05233.
References
- Grüter R, Trachsel T, Laube P, et al., 2022: Expected global suitability of coffee, cashew and avocado due to climate change. PLOS ONE 17, e0261976.
- Inoue H, Takahashi B, 1990: Studies on the bearing behavior and yield composition of the avocado tree. Journal of the Japanese Society for Horticultural Science 59, 487-501.
- IPCC, 1996: Climate change 1995: Economic and social dimensions of climate change. Contribution of Working Group III to the Second Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge.
- IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge and New York.
- Ishizaki NN, 2021: Bias Corrected Climate Scenarios over Japan Based on CDFDM Method Using CMIP6, (NIES2020) ver.1. NIES. https://doi.10.17595/20210501.001. (Reference Date, 2021/10/27).
- Kisaki K, Yoshimatsu T, Uchino K, et al., 2024: Relationship between winter air and leaf temperature and cold damage in ‘Bacon’ avocado tree. Research for Tropical Agriculture 17, 12-17.
- Konakahara M, 1984: Cold injuries on citrus trees and the practical management for their protection. Journal of Agricultural Meteorology 39, 315-322.
- Kondo T, Honsho C, 2018: Effect of shading on low-temperature damage in ‘Bacon’ avocado (Persea americana). Tropical Agriculture & Development 62, 132-135.
- Konno S, Sugiura T, 2024: Experimental study on cold tolerance thresholds in field grown subtropical fruit trees. Journal of Agricultural Meteorology 80, 90-97.
- MAFF, 2020a: Basic plan for food, agriculture and rural areas. Ministry of Agriculture, Forestry and Fisheries of Japan (MAFF). https://www.maff.go.jp/j/keikaku/k_aratana/attach/pdf/index-13.pdf.
- MAFF, 2020b: Basic policy for the promotion of fruit tree farming. https://www.maff.go.jp/j/seisan/ryutu/fruits/attach/pdf/index-96.pdf.
- MAFF, 2024: Statistics of agriculture, forestry and fisheries. https://www.maff.go.jp/j/tokei/index.html.
- Ohno H, Sasaki K, Ohara G, et al., 2016: Development of grid square air temperature and precipitation data compiled from observed, forecasted, and climatic normal data. Climate in Biosphere 16, 71-79.
- Sato K, Ikoma Y, 2020: Effects of elevated temperatures during the flowering to physiological fruit drop stage and at the fruit maturation stage on fruit quality of the satsuma Mandarin. Journal of Agricultural Meteorology 76, 29-35.
- Sato K, Ikoma Y, Matsumoto H, et al., 2015: Effects of spray concentrations and spray times of gibberellin and Prohydrojasmon on peel puffing and peel color in satsuma Mandarin fruit. Horticultural Research (Japan) 14, 419-426.
- Sato K, Okuda H, Iwasaki M, et al., 2010: Influence of 2°C increase under controlled air temperature on physiological fruit drop in citrus. Horticultural Research (Japan) 9, 159-164.
- Shimada A, Kozai N, Yamamoto M, 2022: An evaluation of cold tolerance of avocado by means of several methods. Research for Tropical Agriculture 15, 95-100.
- Sugiura T, 2019: Three climate change adaptation strategies for fruit production. In Climate Smart Agriculture for the Small-Scale Farmers in the Asian and Pacific Region (ed by Shirato Y). NARO, Tsukuba, pp. 277-292. https://www.naro.go.jp/english/laboratory/niaes/publications/fftc_marco_book2019/.
- Sugiura T, Kuroda H, Sugiura H, 2007: Influence of the current state of global warming on fruit tree growth in Japan. Horticultural Research (Japan) 6, 257-263.
- Sugiura T, Sakamoto D, Koshita Y, et al., 2014: Predicted changes in locations suitable for Tankan cultivation due to global warming in Japan. Journal of the Japanese Society for Horticultural Science 83, 117-121.
- Sugiura T, Sumida H, Yokoyama S, et al., 2012: Overview of recent effects of global warming on agricultural production in Japan. Japan Agricultural Research Quarterly 46, 7-13.
- Sugiura T, Yokozawa M, 2004: Impact of global warming on environments for Apple and satsuma Mandarin production estimated from changes of the annual mean temperature. Journal of the Japanese Society for Horticultural Science 73, 72-78.
- Uchino K, Hamashima A, Iwata K, et al., 2019: Effect of low temperature on avocado, litchi and papaya in Kagoshima Prefecture from December 2015 to January 2016. Research for Tropical Agriculture 12, 31-35.
