2 Materials and methods
2.1 Climate variables
For the current climate (1950–2000) we used the WorldClim global climate data set on 2.5 arcminute resolution (Hijmans et al. 2005). The dataset provides interpolated climate layers for 19 bioclimatic variables based on historical data. These variables represent patterns found in monthly weather station data, e.g. annual temperature and precipitation extremes, seasonality and means.
We used five GCMs from the IPCC’s 5th assessment report (Stocker et al. 2013) to obtain future climate data (GFDL-ESM2M, HadGEM2-ES, IPSL-CM5A-LR, MIROC-ESM-CHEM, and NorESM1-M). These GCMs are representative of projected changes of global mean temperature and precipitation (Warszawski et al. 2014). We downscaled the outputs of the GCMs using the delta method (Ramirez and Jarvis 2010) and computed the difference between model outputs for current conditions and the mean for the 2040–2069 time-slice. We smoothed the resulting layers to 2.5 arcminute resolution and applied them to the WorldClim layers for current climate. The result was a high-resolution surface corrected for bias for the current climate and the 2050 time-slice for the 19 bioclimatic variables.
2.2 Present occurrence data
Present occurrence location data identify climates currently suitable to produce coffee. We derived the occurrence points from three sources: (i) Geo-referenced coffee farms; (ii) geo-referenced municipalities in Brazil that produce coffee; and (iii) geo-referenced coffee-growing areas identified from Google Earth where data sources (i) or (ii) were not available.
Most occurrence points came from a global database of 62,000 geo-referenced individual farms with predominantly C. arabica and some C. canephora. The International Center for Tropical Agriculture (CIAT) developed the database during several regional projects that were conducted in collaboration with coffee cooperatives and cooperating research organizations.
A comprehensive set of occurrence records in all coffee-producing regions is desirable so that all suitable climates are represented in the database (Elith et al. 2011). We supplemented the geo-referenced data by generating additional occurrence points using publicly-available information about the distribution of coffee production. We used satellite imagery to identify precise locations based on this information.
Unlike the C. canephora data, data of the C. arabica locations were not collected for modeling so that they were highly clustered in the project regions. We stratified the database to avoid bias using a principal-component analysis on the 19 bioclimatic variables to identify typical climates. From each climate cluster we chose a random representative sample. This reduced the original sample to 1772 unique presence locations for C. arabica.
Neither the Arabica nor the Robusta database included all of the dominant growing regions in Brazil, where 36 % of global Arabica coffee is produced (USDA 2012). To ensure sufficient representation of Brazilian sites and climates, we included data provided by IBGE (2012). Using these data, we identified municipalities where 75 % of the coffee is from one or other of the two species. We then geo-referenced these municipalities for the appropriate species.
2 Materials and methods2.1 Climate variablesFor the current climate (1950–2000) we used the WorldClim global climate data set on 2.5 arcminute resolution (Hijmans et al. 2005). The dataset provides interpolated climate layers for 19 bioclimatic variables based on historical data. These variables represent patterns found in monthly weather station data, e.g. annual temperature and precipitation extremes, seasonality and means.We used five GCMs from the IPCC’s 5th assessment report (Stocker et al. 2013) to obtain future climate data (GFDL-ESM2M, HadGEM2-ES, IPSL-CM5A-LR, MIROC-ESM-CHEM, and NorESM1-M). These GCMs are representative of projected changes of global mean temperature and precipitation (Warszawski et al. 2014). We downscaled the outputs of the GCMs using the delta method (Ramirez and Jarvis 2010) and computed the difference between model outputs for current conditions and the mean for the 2040–2069 time-slice. We smoothed the resulting layers to 2.5 arcminute resolution and applied them to the WorldClim layers for current climate. The result was a high-resolution surface corrected for bias for the current climate and the 2050 time-slice for the 19 bioclimatic variables.2.2 Present occurrence dataPresent occurrence location data identify climates currently suitable to produce coffee. We derived the occurrence points from three sources: (i) Geo-referenced coffee farms; (ii) geo-referenced municipalities in Brazil that produce coffee; and (iii) geo-referenced coffee-growing areas identified from Google Earth where data sources (i) or (ii) were not available.Most occurrence points came from a global database of 62,000 geo-referenced individual farms with predominantly C. arabica and some C. canephora. The International Center for Tropical Agriculture (CIAT) developed the database during several regional projects that were conducted in collaboration with coffee cooperatives and cooperating research organizations.A comprehensive set of occurrence records in all coffee-producing regions is desirable so that all suitable climates are represented in the database (Elith et al. 2011). We supplemented the geo-referenced data by generating additional occurrence points using publicly-available information about the distribution of coffee production. We used satellite imagery to identify precise locations based on this information.Unlike the C. canephora data, data of the C. arabica locations were not collected for modeling so that they were highly clustered in the project regions. We stratified the database to avoid bias using a principal-component analysis on the 19 bioclimatic variables to identify typical climates. From each climate cluster we chose a random representative sample. This reduced the original sample to 1772 unique presence locations for C. arabica.Neither the Arabica nor the Robusta database included all of the dominant growing regions in Brazil, where 36 % of global Arabica coffee is produced (USDA 2012). To ensure sufficient representation of Brazilian sites and climates, we included data provided by IBGE (2012). Using these data, we identified municipalities where 75 % of the coffee is from one or other of the two species. We then geo-referenced these municipalities for the appropriate species.
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