Drought atlas: cocoliztli years were wet in central Mexico; the 16th-century megadrought was northern

scripts/coco_drought.py, Mexican Drought Atlas, central highlands (18.5-20.5 N, 100.5-97 W, 28 cells). Pre-set tests: drought in the year before - not found (mean z +0.34; the opposite of drought); rain returning (rise from the year before) - weak (p 0.14). Exploratory: epidemic years wetter than normal (all 14: mean z +0.61, p 0.008; the 4 major: +1.12, p 0.008). 1540 to 1580 in the central highlands is the 3rd wettest 41-year stretch of 573 since 1400, while Durango in the north is the 14th driest. All four major epidemics came in a wet year 2 to 5 years after a drought year (p 0.014, exploratory, 4 cases).