A new perspective on drought history in the Four Corners: cool- and monsoon-season precipitation reconstructions for the Hopi and Navajo tribal lands

For well over a decade, the Hopi Tribe and Navajo Nation located in northeastern Arizona have suffered the effects of persistent drought conditions. Severe dry spells have critically impacted natural ecosystems, water resources, and regional livelihoods including dryland farming and ranching. Drought planning and resource management efforts in the region are based largely on the instrumental record of climate, which contains a limited number of severe, sustained droughts. In this study, a network of new, moisture-sensitive tree-ring chronologies provides the basis for evaluating the longer-term temporal variability of precipitation in the Four Corners region. By analyzing the earlywood and latewood components within each annual tree ring, we are able to generate separate, centuries-long reconstructions of both cool- (October-April) and monsoon-season (July-August) precipitation. These proxy records improve our understanding of regional drought characteristics over the past 400 years and reveal new insights into seasonal precipitation variability. In particular, the reconstructions suggest that many of the historically significant droughts of the past (e.g. 17th century Puebloan Drought) were not merely winter phenomena, but persisted through the summer season as well. Through the use of two different analysis techniques, we identify both short-term and decadal-scale drought events more severe than any in the instrumental record. Moreover, by comparing these proxy records with evidence of drought from historical documents, we are able to independently validate the reconstructions and gain insights into the socioeconomic and environmental significance of past climate anomalies on the tribal lands of northeastern Arizona.