One hundred years of climate change in Mexico

surface (i.e., gridpoints) of land areas were generated with the function LAPGRD, using a 30-arc second of spatial resolution digital elevation model (https://lta.cr.usgs.gov/GTOPO30). As an additional output, we derived 19 bioclimatic variables for each period with the dismo library [50] of R software [51]. These variables included annual, quarterly and monthly sum- maries of temperature and precipitation that represent more biologically meaningful variables than the original climate surfaces and have been widely used in several studies of climate change impacts on species and ecosystems [12]. For t1-1940, we used 803 stations for precipita- tion and 500 for minimum and maximum temperatures. For t2-1970, the number of stations was 3411 and 3670 for precipitation and temperature, respectively. For t3-2000, the number of stations was 3870 and 4200 for precipitation and temperature, respectively (Fig 1). Across the country, 47% of the weather stations are located in mountainous regions above 1500 masl; the remaining 63% are located in the lowlands. Data used for the analysis are available upon request, and the original dataset is available at the National Meteorological Office (http://smn. cna.gob.mx/es/, S1 File). Monthly climate surfaces and bioclimatic variables for each period are freely available (see URLs in Table 1). In order to evaluate differences between periods, we performed a discriminant analysis on deseasoned climatic surfaces using the Statistica software version 10 [52]. Deseasoning is rec-

ommended to eliminate seasonality from the analysis that may obscure temporal changes. To do so, we calculated standardized anomalies (z-scores) for each month of the three periods using the Deseason Panel of the Earth Trends Modeler (ETM) of Idrisi Selva [53]. We also evaluated if the difference in the number of weather stations between t2-1970 and t3-2000 had an effect on the climate surfaces; we did not compare t1-1940 against the other two periods because station instrumentation and especially density was quite different for the first period from that of the last two periods [40]. In order to compare t2-1970 and t3-2000, we created a Table 1. URLs for downloading monthly gridded surfaces of maximum temperature, minimum temperature and precipitation, and 19 bioclimatic parameters. Metadata can be accessed through the metadata tab. Variable Period url Monthly maximum temperature (MaxT) t1-1940 (1910– 1949) http://geoportal.conabio.gob.mx/metadatos/doc/html/ tm191049gw.html t2-1970 (1950– 1979) http://geoportal.conabio.gob.mx/metadatos/doc/html/ tm195079gw.html t3-2000 (1980– 2009) http://geoportal.conabio.gob.mx/metadatos/doc/html/ tm198009gw.html Monthly minimum temperature (MinT) t1-1940 (1910– 1949) http://geoportal.conabio.gob.mx/metadatos/doc/html/ tmi191049gw.html t2-1970 (1950– 1979) http://geoportal.conabio.gob.mx/metadatos/doc/html/ tmi195079gw.html t3-2000 (1980– 2009) http://geoportal.conabio.gob.mx/metadatos/doc/html/ tmi198009gw.html Monthly precipitation (Ppt) t1-1940 (1910– 1949) http://geoportal.conabio.gob.mx/metadatos/doc/html/ p19101949gw.html

t2-1970 (1950– 1979) http://geoportal.conabio.gob.mx/metadatos/doc/html/ p19501979gw.html t3-2000 (1980– 2009) http://geoportal.conabio.gob.mx/metadatos/doc/html/ p19802009gw.html 19 Bioclimatic variables (Bio) t1-1940 (1910– 1949) http://geoportal.conabio.gob.mx/metadatos/doc/html/ b19101949gw.html t2-1970 (1950– 1979) http://geoportal.conabio.gob.mx/metadatos/doc/html/ b19501979gw.html t3-2000 (1980– 2009) http://geoportal.conabio.gob.mx/metadatos/doc/html/ b19802009gw.html https://doi.org/10.1371/journal.pone.0209808.t001 PLOS ONE Historical climate change in Mexico PLOS ONE | https://doi.org/10.1371/journal.pone.0209808 July 16, 2020 5 / 19