A Preliminary Analysis of the Impacts of Climate Change on the Reliability on West Side Water Supplies Richard Palmer and Margaret Hahn Department of Civil and Environmental Engineering University of Washington

Talk Overview Challenges of urban water supply Infrastructure today Future water demand Change in streamflows Ability to provide drinking water Responding to climate change

Points to be made Climate change will impact the watersheds providing urban supplies Growing water demands will also stress urban supplies Competition for water will increase during periods when less is available Long-lead time, adaptive planning is needed to face these challenges

Environmental Stewardship Growing Urban Demands Climate Change

The Basic Problem Water Demands Precipitation Because these are out of sync, storage in the form of snowpack or reservoirs is essential

Winter Spring Summer Fall Storage in Reservoirs Simple Operation Concepts Top of Dam Dead Storage Active Storage Annual Drawdown

Winter Spring Summer Fall Flow in River Flows for Fish Streamflows Target Flows

Urban Water Challenges Goals: Provide –Safe –Reliable –Inexpensive water Utilities must balance goals with –Environmental stewardship –Cost –Performance –Desires of multiple customers

Current Expansion

Urban Water Resources The urban areas are served by an infrastructure that was constructed in the early and mid-20th century The yield of some of these systems is not significantly larger than today’s demands Interties within the region and new sources provide interesting alternatives

Urban Water Demands Influences –Population, Industry, Housing mix, Lot size –Weather conditions temperature precipitation –Plumbing Codes –Public Response

Water Demands Puget Sound area water demand is expected to increase in average years from 435 to nearly 500 mgd (15%) by 2020 The Portland area demand is expected to grow from 120 to 150 mgd (25%) by 2020 This increase in demand will stress systems that are already near system yields

Evaluation of Climate Impacts Meteorological data Hydrology model Calibration Climate Shift Impacts Evaluation Precip and temp DHSVM Historic vs Simulated Downscaled GCM CRYSTAL model

Impacts on Streamflow Climate change by 2040 will significantly impact the timing of the region’s runoff The lack of late spring snowpack will decrease the “stored” water available for the summer This will extend the draw-down period and make the region more susceptible to drought

Impacts on Storage Climate change by 2040 will significantly impact the annual minimum storage Storages similar to those encountered in 1987 and 1992 will become more common place, even with no increases in demands Significant changes in operations and/or available infrastructure will be required.

Summary Climate change will impact the amount and timing of when streamflows will be available The changes in flows will impact storages in urban water supply reservoirs making curtailments more likely Solutions to these problems require careful, long-term adaptive planning to ensure consideration of the most effective alternatives