Projected Climate Changes
The water along Seattle’s Puget Sound shoreline has risen by more than 6 inches during the past century. Climate change is expected to accelerate rising sea levels during the next century. Mean projections indicate that Seattle will experience 7 inches of sea-level rise by 2050, and 24 inches by 2100. (The highest projection indicates 19 to 56 inches by 2050 and 2100, respectively.) While chronic inundation is a concern, sea-level rise impacts will first be noticed episodically with more frequent tidal flooding events. Water levels associated with storm surges and “king tides” (annually occurring extreme events) today will eventually become monthly, even daily events. Seattle Public Utilities (SPU) has developed tools to help visualize and evaluate impacts of sea-level rise scenarios.
Rainfall is expected to become more intense in many parts of the world, including the Pacific Northwest. However, the magnitude of change in Seattle has been difficult to model because of the complex terrain that surrounds us among other factors. In addition, historical observations only slightly indicate increased rainfall intensities. That said, Seattle has experienced a fair share of extreme weather events in recent years, and SPU is exploring how to better prepare for the potential of more extreme events (pdf).
Not typically associated with heat, Seattle has averaged only a handful of 90°F days per year during the past few decades. By the end of this century, such events are expected to become more common, with more than two weeks of 90°F days likely each summer. Also certain to increase are nighttime temperatures and humidity. Increased temperatures will likely increase water demand, which SPU feels it can address through its comprehensive water conservation program.
Pacific Northwest winters are projected to become warmer and wetter, and summers warmer and drier. That means more rain than snow falling on the Cascade Mountains and eventually more prolonged periods of drought. It also likely means changing forests, stressed salmon habitat, and even wildfires. SPU has assessed potential impacts (pdf) to our water supply and identified some adaptation options and is committed to updating these assessments and options periodically and researching related issues as needed.