An assessment of drought on maize cropping success in ancient Maya lowlands during the last half of the first millennium ce

Drought arising from a shift in intertropical convergence zone in the Yucatán peninsula during the last half of the first millennium is often cited as a determining cause in the collapse of ancient Maya polities. Some Mayanists have postulated that a small change in precipitation might have been sufficient to result in catastrophic cropping failure, with attendant large decline in population. The supporting data for this conjecture are essentially very weak. In particular, paleoclimatologists could provide only qualitative drier or wetter periods. The data resolution has not been at the level of daily or monthly precipitation in ancient times. It is well known in the cropping of maize that the pattern, frequency, and quantity of precipitation, among other things, during the growing period are of paramount importance. Present quantitative assessment suggests that a decrease of the order of 40%, uniformly over a 125-day growing season, from normal precipitation may not have an adverse impact on maize cropping success. This finding presents doubts in the hypothetical climate-based cause of catastrophic decline in population during the period of ‘Maya collapse’.