One hundred years of climate change in Mexico

change in mean precipitation is smaller between t2-1970–t3-2000 than between t1-1940–t2- 1970 (Table 3). Mean changes in annual precipitation since t2-1970 ranged between 4% increase for the Nearctic to -5% for the Neotropical region. Despite the change in mean precip- itation in the Nearctic was positive, median conditions between t2-1970–t3-2000 have decreased. Changes in precipitation were higher in the Transition Zone and the Neotropical region than in the Nearctic region, with a reduction of precipitation of 3% to 8%, respectively (Table 3). Precipitation has generally decreased in the tropical provinces of the south and in the mountainous provinces of the Transition Zone, whereas it has increased in the Nearctic prov- inces for both temporal changes (Fig 4). In several southern biogeographic provinces, the mag- nitude of precipitation decreased in t2-1970–t3-2000, mainly during spring (MAM) and autumn (SON; Fig 4). Mean precipitation change was higher from t1-1940 to t2-1970 in five biogeographic provinces (Sierra Madre del Sur, Costa del Pacı´fico, Oaxaca, Soconusco, and Golfo de Me´xico) compared to the mean precipitation change from t2-1970 to t3-2000. In the remaining provinces, the precipitation change was positive in t1-1940–t2-1970, but magnitude decreased in t1-1940–t2-1970 (Fig 4). Monotonic upward or downward change in Bio 12, Bio 05 and Bio 06 occurred over 50% of the interpolated climate surfaces (Fig 5). A consistent reduction in maximum temperature (Bio 05) occurred in 13% of the country, whereas 12% of the country experienced an increase

in this parameter. Minimum temperature (Bio 06) decreased monotonically in 26% of the country and consistently increased in 12% of the country. For precipitation (Bio 12), consis- tent increases and reductions were observed in 18% and 5% of the country, respectively, mainly in the Altiplano Norte, Sierra Madre Occidental, Sonorense, Baja California, and Pete´n provinces. Positive changes in Bio 06 were particularly consistent in the mountainous regions Table 2. Average temperature changes from t1-1940 to t2-1970 and from t2-1970 to t3-2000. Annual mean temperature changes (˚C) Region Statistics t1-1940� to t2-1970 t2-1970 to t3-2000 Mexico Mean -0.32 0.22 Median -0.28 0.30 10th percentile -1.10 -0.46 90th percentile 0.45 0.69 Nearctic Mean -0.43 0.30 Median -0.33 0.28 10th percentile -1.34 -0.26 90th percentile 0.49 0.89 Transition Zone Mean -0.39 0.03 Median -0.42 0.06 10th percentile -1.33 -0.45 90th percentile 0.56 0.49 Neotropical Mean -0.64 0.06 Median -0.70 0.08 10th percentile -1.45 -0.43 90th percentile 0.26 0.48 Summary statistics were computed for Mexico and for three biogeographic regions. To calculate the statistics, we used the grid points (at 30-arc second spatial resolution) that fell within a particular province. Stations used were not corrected for inhomogeneities and densities vary between periods, especially between t1-1940 to t2-1970. �This period is longer than t2-1970 and t3-2000. https://doi.org/10.1371/journal.pone.0209808.t002 PLOS ONE Historical climate change in Mexico

PLOS ONE | https://doi.org/10.1371/journal.pone.0209808 July 16, 2020 9 / 19