Expected global suitability of coffee, cashew and avocado due to climate change

Coffee The drastic overall decrease in coffee suitability by 2050 that was found in this study is in line with the results of existing climate change impact studies for coffee arabica [2, 3, 10, 11]. Coffee is described as a crop which is highly sensitive to climate change. As in the present study, Bunn et al. [2] and Ovalle-Rivera et al. [3] show overall reductions in global suitable areas for coffee, mainly at low latitudes and low altitudes. According to Ovalle-Rivera et al. [3], the impacts of climate change on coffee suitability are extremely variable at national and global levels, confirming our findings. The decrease in suitable area by about 50% across scenarios by 2050 shown by Bunn et al. [2] is in a similar range compared to the more than 50% reductions in S1 and 30–50% reductions in S2 found in this study. In addition, the main producing regions (Brazil, Vietnam, Indonesia, Colombia) are also expected to experience substantial reductions in suitable areas for coffee cultivation [2, 3, 10]. In accordance with our findings, few regions in East Africa, Asia and South America are described to potentially be able to bene- fit from climatic change [2, 3, 10, 11]. They are generally at higher elevations or at the latitudi- nal boundaries of the growing regions. Potential future growing regions around South Brazil, Uruguay and Northern Argentina were explicitly studied by Zullo et al. [11], and have also been identified here. Several other regional studies have investigated coffee arabica suitability

changes in Mesoamerica [7, 8], Nepal [9], East Africa [5, 6] and Zimbabwe [4]. However, areas of increasing suitability in South China identified in this study have not been mentioned in previous investigations. In all coffee modelling studies mentioned above, temperature variables were the most important factors explaining decreasing suitability, except for Chemura et al. [4] who found changes in the distribution of precipitation were most important in Zimbabwe. This is in line with our results, where temperature variables are mainly responsible for future changes. Additionally, no previous models took land and soil requirements into account which limited coffee suitability in some areas of all growing regions. This is important in modelling studies for planning new coffee plantations only in areas where coffee is locally adapted and requires a minimum of additional inputs and where there are no major environ- mental trade-offs. Cashew In contrast to coffee, much less research is available about the biophysical suitability of cashew and avocado. For cashew, no global assessment of current and future growing regions is cur- rently available. Cashew suitability maps are available for Ghana and Coˆte d’Ivoire [14], Malawi [13], India [15] and Lombok Island in Indonesia [16, 17]. Climate change impacts were only modelled for Ghana and Coˆte d’Ivoire [14]. A few more studies are available on cli- mate change perceptions of cashew growers [42] and the impact of climate factors on cashew productivity [43] in Benin, and about the socio-economic and environmental impacts of

cashew expansion in Guinea-Bissau [44–46]. In contrast to CIAT [14] who identified large areas with a positive impact of climate change on cashew suitability in Coˆte d’Ivoire and Ghana by 2050, no change or slight reductions in suitability were modelled in our study for these regions. This is most probably due to the different methodology (maximum entropy modelling) applied in their study [14], which is based on the current distribution of cashew production, while our model is based on the biophysical requirements of the crop. In fact, the cashew suitability within the current growing regions modelled by CIAT [14] is to a great extent consistent with our findings. While the current cashew suitability in Malawi matches with the suitability map of Benson et al. [13] for rainfed cropping under traditional manage- ment, it is not comparable with the findings of Widiatmaka [17] for Lombok Island in Indone- sia, due to different criteria applied in the former’s model. However, comparing our results PLOS ONE Global suitability of coffee, cashew and avocado PLOS ONE | https://doi.org/10.1371/journal.pone.0261976 January 26, 2022 19 / 24

with the major growing regions in India [15] and West Africa [47] reveals that based on long dry seasons, cashew suitability is underestimated in some of these regions, as was mentioned above. Avocado Similar to cashew, only a limited number of assessments of avocado growing regions are avail- able. The most comprehensive characterisation of current and future distributions of avocado was undertaken by Ramı´rez-Gil et al. [18] across the Americas. Avocado suitability was also studied in Mexico [29, 48], Colombia [49], Brazil [50], Turkey [20] and Australia [19]. Sub- stantial differences were identified between the suitable avocado growing regions modelled in our study and by Ramı´rez-Gil et al. [18]. While in some regions (e.g. Colombia, Honduras or Nicaragua), current avocado suitability is similar, it is higher in their study in parts of Uruguay, Argentina, Chile, Peru, Mexico or the USA, and lower in parts of Brazil, Bolivia, Venezuela, Guyana or Surinam. We explain these differences by the ecological niche modelling approach applied by Ramı´rez-Gil et al. [18] which is based on current production locations, some of which coincide with arid zones unsuitable for avocado cultivation under rainfed conditions. In accordance with our findings, Ramı´rez-Gil et al. [18] identified expansion of growing regions due to increasing temperatures mainly in temperate areas (e.g. Argentina). Contractions of suitable ranges were mainly related to temperature and precipitation increases, while in our

model they were related to both drier and wetter conditions but not temperature increases. Based on reported heat stress effects during critical periods such as pollination and fruit set [30], we therefore conclude that the requirements at high temperatures are not restrictive enough in our model. The current production locations in Colombia as reported in Ramı´rez- Gil [49] and in the Parana´ River Basin in Brazil described by Caldana et al. [50] lie within suit- able areas based on our model. The main producing municipalities in Mexico (Michoaca´n State) presented in Lira-Noriega et al. [51] are only marginally suitable due to a long dry season and can be confirmed by required supplemental irrigation in this region as flowering and early fruit development occur in a dry period [30]. Based on the analysis of Charre-Medellı´n et al. [48], avocado suitability will decrease in this region by 2050, an aspect which was not found in our study. Selim et al. [20] identified suitable growing areas for avocado at the Mediterranean coast in Antalya, Turkey, where according to our model, suitability will increase with climate change due to increasing temperatures. In Australia, Putland et al. [19] identified suitable avo- cado growing regions in southwest Western Australia, along the Murray River and in coastal New South Wales, which were rated as too cold or too dry in our model. As mentioned above, cultivation is only possible in these regions with irrigation or measures against frost. Modelling approach

The multi-criteria evaluation approach used in this study is based on crop requirements and respective bioclimatic and soil data, unlike other bioclimatic crop modelling approaches that are based on current production locations, such as maximum entropy modelling [52]. It is therefore a transparent approach especially suitable for identifying limiting factors for crop growth but there are also limitations associated with it. As mentioned in the methodology, our model does not take into account management options such as irrigation or liming. Important production locations are therefore rated as not suitable, or only marginally suitable, as was shown above. There are also no interactions modelled between different criteria (e.g. between precipitation and soil texture), that could potentially affect suitability. We also did not discrim- inate between different varieties of the same crop but took this variation into account when defining the ranges of the different suitability classes. The modelling of climate change impacts PLOS ONE Global suitability of coffee, cashew and avocado PLOS ONE | https://doi.org/10.1371/journal.pone.0261976 January 26, 2022 20 / 24

tions were found for all three crops. Coffee proved to be most vulnerable to climate change with negative impacts dominating in all growing regions, primarily due to increasing tempera- tures. Compared to coffee, cashew and avocado were found to be more resilient to climate change. For cashew, which showed the highest suitability range, both positive and negative effects of climate change were found. While globally, the suitable cashew growing areas are expected to increase, in some of the main producing countries (e.g. India, Coˆte d’Ivoire and Benin), areas of high suitability are expected to decrease. Similarly, for avocado, the suitable areas are expected to expand globally, while the most suitable areas in some of the major pro- ducing countries (e.g. the Dominican Republic, Peru, Indonesia) might decrease. All three crops however profit from increasing minimum temperatures at high latitudes and high altitudes. The study has shown that climate change adaptation will be necessary in most major pro- ducing regions of all three crops. Adaptation measures can include site-specific management options, plant breeding efforts for varieties that are better adapted to higher temperatures or drought and in the case of coffee, replacement of arabica with robusta coffee in certain regions [2]. New production locations at higher altitudes and latitudes might create new market opportunities. However, policies and strategies are required to ensure that shifts in production locations will not lead to negative environmental impacts such as deforestation, loss of biodi-

versity or ecosystem services. Additionally, landowners and farmers in current and future pro- duction locations must be willing to change their management or grow a new crop. Therefore, adaptation measures and shifts in production will each have to be addressed in participative approaches that allow the engagement of local stakeholders. Acknowledgments We extend our thanks to Hanno Rahn for his support in geodatabase management, to Pascal Ochsner and Nikolaos Bakogiannis for their advice in spatial data analysis, to Dominik Klauser for his expert advice on the selection of crops, and to Caroline Hyde-Simon for proofreading. PLOS ONE Global suitability of coffee, cashew and avocado PLOS ONE | https://doi.org/10.1371/journal.pone.0261976 January 26, 2022 21 / 24

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