Adapting our infrastructure and institutions to climate change is a crucial dilemma for modern society. Archaeologists should be well positioned to address this issue with examples from the past. Yet, too often when we find that cultural changes are synchronous with climate variation, such as abandonment of a region during a drought, we advance causal arguments to what may merely be correlations. I argue that identifying proxies for resource management in the archaeological record, particularly for resources managed by collective action and vulnerable to climate change, can help to address this problem. To test this approach I studied water management practices of Ancestral Pueblo communities living on the highland mesa-tops of the Jemez Mountains of New Mexico. Between AD 1100-1700 cultural histories across this region diverged. Ancestral Towa communities of the Jemez Plateau sustained high populations until Spanish removal in the 17th century. The adjacent Pajarito Plateau was nearly completely depopulated by ancestral Tewa and Keres communities by the early 16th century. Archaeologists hypothesize that droughts were a factor in pushing people off the Pajarito Plateau, yet the endurance of communities on the Jemez Plateau is unconsidered. Mesa-top communities in both regions constructed artificial water reservoir features, which historical Pueblo communities managed as common pool resources. I hypothesize that these archaeological features reflect collective action decision-making for managing water, a resource vulnerable to scarcity on these mesa-tops during droughts, and that decisions made about water management influenced the long-term sustainability of Ancestral Pueblo communities. Through diachronic socio-hydrological modeling, I identify how climate variation influenced feedbacks between resource users, water infrastructure, and hydrological systems. I conducted modeling of paleohydrological system responses to droughts, direct geoarchaeological investigations of fifteen reservoirs at nine Ancestral Pueblo villages, and geospatial analyses of water access. My hydrological modeling found that the Pajarito Plateau is more vulnerable to hydrological droughts than the Jemez Plateau. My geoarchaeological investigations found that communities on the Jemez Plateau built reservoirs before droughts when populations were low, and that reservoirs were used and maintained through their entire occupation histories. By contrast, communities of the Pajarito Plateau built reservoirs in the early 1300s when hamlets were coalescing into villages at the peak of regional populations. All of the reservoirs on the Pajarito Plateau, as well as many of the villages with reservoirs, were then abandoned by the mid-1400s. Through least cost analyses from hundreds of water sources to thousands of archaeological sites I found that water costs became much higher during droughts on the Pajarito Plateau, which was further exacerbated by the pooling of resources (and risks) in aggregated communities. Therefore, it cannot be ruled out that an over-reliance on collective action approaches to water management made communities on the Pajarito Plateau more vulnerable to hydrological droughts than communities on the Jemez Plateau. My work shows how archaeological research into resource management, employing earth science methods and common pool resource theory, contributes to dialogs surrounding adaptations to climate change.
Common Goods in Uncommon Times: Water, Droughts, and the Sustainability of Ancestral Pueblo Communities in the Jemez Mountains, New Mexico, AD 1100-1700