The Delaware River provides half of New York City's drinking water, is a habitat for wild trout, American shad and the federally endangered dwarf wedge mussel. A drought during the 1960s stands as a warning of the potential vulnerability of New York City to severe water shortages. The water releases from three New York City dams on the Delaware River's headwaters impact not only the reliability of the city's water supply, but also the potential impact of floods, and the quality of the aquatic habitat in the upper river. The Delaware water release policies are constrained by the dictates of two US Supreme Court Decrees (1931 and 1954) and the need for unanimity among four states: New York, New Jersey, Pennsylvania, and Delaware, and New York City. Coordination of their activities and the operation under the existing decrees is provided by the Delaware River Basin Commission (DRBC). Questions such as the probability of the system approaching drought conditions based on the current Flexible Flow Management Plan and the severity of the 1960s drought are addressed using long record paleo-reconstructions of flows. For this study, we developed reconstructed total annual flows for 3 reservoir inflows using regional tree rings going back upto 1754 (a total of 246 years). The reconstructed flows are used with a simple reservoir model to quantify droughts. We observe that the 1960s drought is by far the worst drought based on 246 years of simulations (since 1754). However, there are intermediate drought warning periods and proper adaptation would be sufficient during these periods. Modified release rules that aid thermal relief to wild trout in the upper Delaware can be explored without much stress to the system during most periods.
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