One hundred years of climate change in Mexico

with greater changes in the north of the country [9]. We also identified a general increase in precipitation throughout the century, although its magnitude decreased between t2-1970 and t3-2000. This change might be related to the fact that a negative Atlantic Multidecadal Oscilla- tion and a Pacific Decadal Oscillation were observed during the last period [9]. Pervasive climatic change leads to changes in species composition, as has been observed for birds in Mexico [28]. Understanding recent climate and ecological changes are useful to focus research efforts and conservation actions; therefore, the climate changes detected in this study may be useful to establish priorities for conservation. For instance, the Transition Zone includes the Sierra Madre Occidental, Sierra Madre Oriental and Eje Neovolca´nico provinces, which harbor diverse types of temperate vegetation, such as oak, pine and cloud forests; all of them, but particularly the latter, are highly vulnerable to climate change [68,69]. The Sierra Madre Oriental harbors the richest coniferous forests in the world [70]. Our results show that this province has been warming since mid-20th century and is projected to be affected by cli- mate change in the future [69,71], thus conservation efforts should be prioritized in this region [70]. Changes in climate are now occurring simultaneously with other environmental disrup- tions. It will not be possible to fully understand biodiversity responses to climate change with- out considering the interactions with other components of environmental change [72]. Species

responses will depend on their exposure and sensitivity to other human-induced pressures, their inherent capacity to adapt to new conditions, the magnitude and speed of environmental changes, and time lags in their responses [1,10,62]. This work aims to serve as a baseline for improving our knowledge regarding historic climate change in Mexico in a spatially-explicit fashion, to identify specific areas where climate change is occurring and to identify its direc- tion and magnitude. In sum, climate change is occurring unevenly in Mexico. Provinces in the Nearctic region showed a higher and more consistent warming over time than provinces from the Transition Zone and Neotropical region. Precipitation has also generally increased more consistently in northern provinces over the whole period, whereas it tended to decrease in most of the Neo- tropical region and Transition Zone between t2-1970 and t3-2000. Nonetheless, it is important to bear in mind that the first period (t1-1940) holds higher uncertainty than the other two given the lower number of weather stations used to produce the climatic surfaces. Finally, this information can be used to improve regional projections of future climate impacts on biodi- versity, which would provide scientists and authorities with more reliable data and informa- tion for making better decisions in the face of climate change. Limitation of the analysis We have generated three sets of climatic surfaces for Mexico with error estimates based on withheld data across the country [42] comparable to errors obtained in two other climate sur-

face datasets developed for the country for different time frames [15,17]. However, it is impor- tant to mention the main shortcomings in this type of data and analysis for a better use of them. First, it has been demonstrated that long-term station records that are used to interpo- late climate surfaces generally suffer from incompleteness and inconsistencies through time caused by equipment failure, replacement or station relocation [40,73], limiting their use for calculating multi-decadal climate trends [72,74]. This is the case for the data that we used for generating these climatic surfaces. Our results of the Pettitt test indicate that a considerable proportion of the stations presented inhomogeneities along the time-series, especially for min- imum temperature (see S1 File). Furthermore, the breakpoint years occurred mostly during the second half of t2-1970 and the first half of t3-2000 (S1, S2, S3 Figs in S1 File). To know how PLOS ONE Historical climate change in Mexico PLOS ONE | https://doi.org/10.1371/journal.pone.0209808 July 16, 2020 14 / 19