An analysis of past and present megadrought impacts on a modern water resource system

Extended drought is a concern for water resource sustainability in the Colorado River Basin of the western USA. Recent instrumental data are a limited rendering of drought risk, while paleoclimate data provide evidence of megadrought that could reoccur; but their impact analyses have not been reported to date. A 645-year tree-ring reconstruction of central Arizona, USA, streamflows reveals several threatening periods including a severe 16th-century multi-decade event. This study translated that record to net basin water supply with comparison to instrumental records to drive an operations model of a key resource system serving metropolitan Phoenix, Arizona. Cumulative system impacts and demand sensitivities find no system depletion to inoperable conditions for any drought of the past several centuries. The megadrought presently afflicting the region has become more severe than any in the paleoclimate record and should be considered the new drought of record for adaptation planning.