A century long ensemble streamflow dataset in the Pacific Northwest to support water security assessments.

In the Pacific Northwest, ensemble projected streamflow datasets are valuable for assessing vulnerabilities and the resilience of reservoir systems across the region. These datasets are typically generated using a climate-hydrologic modeling chain that begins with coarse-resolution outputs from selected Earth System Model (ESMs) and socioeconomic scenarios, which are spatially downscaled, followed by hydrologic simulations driven by the downscaled meteorological forcing. In this work, a calibrated catchment-based hydrology and river model is forced by ESM outputs for several socioeconomic scenarios from the archives of the Coupled Model Intercomparison Project phases 5 and 6, which are downscaled using a computationally efficient weather model. The dataset comprises twenty-nine daily hydrologic traces from 1950 to 2099 for 18,000 river reaches. The dataset also includes a retrospective hydrologic simulation forced by an observation-based meteorological dataset used for hydrologic model calibration. Naturalized flows for 221sites are used to assess historical simulation fidelity. This dataset supports a variety of applications including reservoir modeling, ecological impact assessments, and hydrologic analyses under historical to projected climate conditions.