Fig. 1.

The climatic and ecoregional dryland gradient along the Pacific coast of Mexico. (A) The dry ecoregions of the Pacific coast: mediterranean California (a), Baja Californian Desert (b), Sonoran Desert (c), Cape Region Thorn-scrubs and Dry Forests (d), Sinaloan Thorn-scrubs and Dry Forests (e), and Tropical Dry Forests (f); the high-elevation oak and conifer forests of the Sierra Madre and the Transversal Volcanic Range are shown for reference (g). The dots in the figure mark the location of the weather stations used in the analysis. (B) Correlation between mean annual SOI values and mean total annual precipitation: Blue dots indicate negative correlation, and red dots indicate positive values. Large dots indicate statistically significant correlations (P < 0.05) according to the F test. (C) Concentration of winter-spring rainfall in Mexico calculated from 1-km resolution interpolated climate surfaces. Blue colors indicate areas with a high proportion of annual precipitation falling between December and April (winter-spring precipitation), and red colors indicate areas where winter-spring rainfall is very low or nonexistent, and hence where summer and fall rains dominate.