DWR’s 2070 extreme climate change scenarios enable exploration of the vulnerability of and opportunities for water supply at the potential bounds of future climate change conditions. These scenarios were originally developed as part of the public benefit uncertainty analysis for the California Water Commission’s Water Storage Investment Program (WSIP) (dataset available here: https://data.cnra.ca.gov/dataset/climate-change-projections-wsip-2030-2070). In 2018, DWR’s Sustainable Groundwater Management Program (SGMP) furnished these extreme scenarios for use by Groundwater Sustainability Agencies (GSAs) (dataset available here: https://data.cnra.ca.gov/dataset/sgma-climate-change-resources). Specifically, downscaled global climate model (GCM) projections were provided for two future climate periods, including a 2030 central tendency, a 2070 central tendency, and two 2070 extreme scenarios to establish a range of projected conditions. **Since then, DWR collaborated with Lawrence Berkeley National Laboratory to improve the fidelity of these long-range planning datasets, resulting in this update of the 2070 extreme scenarios.** The 2070 extreme scenario update utilizes an improved climate period analysis method to better capture the GCM-projected change in temperature and precipitation. The updated dataset improves downscaled climate change extreme conditions considered for water supply that features both statewide coverage of hydrologic variables and managed flows within California’s inter-regional water conveyance system. **A technical note on the background and results of this process is provided here**: https://data.cnra.ca.gov/dataset/extreme-climate-change-scenarios-for-water-supply-planning/resource/f2e1c61a-4946-4863-825f-e6d516b433ed.