One hundred years of climate change in Mexico

water availability [62], as has been observed in Tamaulipeca, Baja California and Sonorense provinces [64,65]. Arid and semiarid provinces are highly dependent on water availability, reg- ulating net ecosystem productivity [62,66] and agriculture [36,64]. Human population and agriculture have increased in these provinces in the last three decades, exceeding water avail- ability in some areas [63,67]. There are large spatial variations in the projected changes of temperature and precipitation in most of the Altiplano Sur and Eje Neovolca´nico provinces, although within the latter we identified an increase in minimum temperature in several high-elevation volcanoes. The rapid retreat of glaciers during the 20th century confirms this observation [68]. The confluence of flora and fauna from the Nearctic and Neotropical regions makes the Transition Zone particu- larly rich and unique [60]. Many species are endemic to this region and occupy naturally nar- row distributional ranges. This condition coupled with the fact that the Transition Zone concentrates the highest human density and largest urban nuclei of the country, its biodiver- sity is highly vulnerable to the synergistic effects of multiple stressors, including climate change [10]. Furthermore, survival of many species depends on their capacity to keep pace with cli- mate; however, their ability to respond to climatic changes via range shifts are limited due to human-induced obstacles, making them highly vulnerable to the current warming event [36,62].

There are several factors other than global warming that also influence climatic variations through time, for instance, the Pacific Decadal Oscillation, the Atlantic Multidecadal Oscilla- tion and the El Niño Southern Oscillation. At a regional scale, the direct attribution of anthro- pogenic climate change to the observed patterns is complicated; nonetheless, our results are in line with those obtained by the IPCC, showing increase in temperature since mid-20th century, Table 3. Average precipitation changes from t1-1940 to t2-1970 and from t2-1970 to t3-2000. Anual Precipitation (mm) Region Statistics t1-1940� to t2-1970 t2-1970 to t3-2000 Mexico Mean 123 (16) -13 (-2) Median 48 (8) 1 (0) 10th percentile 28 (11) 23 (8) 90th percentile 26 (2) 164 (10) Nearctic Mean 3 (1) 18 (4) Median 35 (10) 18 (5) 10th percentile 3 (1) 18 (13) 90th percentile 41 (7) -1 (0) Transition zone Mean 141 (16) -12 (-1) Median 121 (15) -13 (-2) 10th percentile 40 (8) 10 (2) 90th percentile 262 (21) -36 (-3) Neotropical region Mean 289 (21) -62 (-5) Median 122 (10) -8 (-1) 10th percentile 139 (16) -28 (-4) 90th percentile 740 (33) -160 (-8) Summary statistics are reported as millimeters and percentages (in parenthesis) and were computed for Mexico and for three biogeographic regions. To calculate the statistics, we used the 30-arc gridpoints 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.t003 PLOS ONE Historical climate change in Mexico PLOS ONE | https://doi.org/10.1371/journal.pone.0209808 July 16, 2020 13 / 19