Long term effects of climate on human adaptation in the middle Gila River Valley, Arizona, America.

The Hohokam, an irrigation-based society in the American South West, used the river valleys of the Salt and Gila Rivers between 500 and 1500 AD to grow their crops. Such irrigated crops are linking human agency, water sources and the general natural environment. In order to grow crops, water available through rain and river flows needs to be diverted to land where the plants are grown. With a focus on the Gila River, this paper uses the potential harvest of maize (a main Hohokam crop) as a proxy for evaluating the influence of natural water availability and climatic changes on irrigation options for maize. Available climate variables derived from tree-ring proxies are downscaled. These downscaled data are used as input for a crop growth model for the entire sequence of Hohokam occupation along the Gila River. The results of the crop model are used to discuss the potential influence of climatic variability on Hohokam irrigation and society. The results will show that climatic change alone cannot be used as an explanation for developments in Hohokam irrigation. Societal development resulting in growing population and extensive irrigation systems increasing pressure on water sources over time would have been a key factor to include to understand Hohokam society between 500 and 1500 AD.