2014/07/16 Council Agenda Packet

The region's rivers include the Snoqualmie, Skykomish, Snohomish, Cedar, Green, Stillaguamish, Sauk, Puyallup, White and Nisqually, among others. Many of these rivers are prone to flooding, and it is not uncommon to see flood events at least once a year due to heavy rain. According to the Federal Emergency Management Agency (FEMA), major flooding occurred on 18 rivers in Western Washington in 2009, with record or near record crests on six rivers. Interstate 5 was under water for the fourth time since 1990. Each county in the central Puget Sound region has information available regarding the floodplain areas within their boundaries, including policy information and guidance for property owners. For example, in October 2009 Snohomish County published a "Guide to Protecting Life and Property in the Floodplain." The five major river systems in Snohomish County — Sauk, Stillaguamish, Skykomish, Pilchuck and Snohomish — have experienced record floods over the past 20 years, and the area impacted by flooding in the county is over 200 square miles. In Pierce County, property owners within or near a 100-year floodplain were sent a Flood Bulletin in 2009. Fifteen presidential disasters have been declared in Pierce County since 1962 due to major flooding. King County's 2006 Flood Hazard Management Plan addresses the needs of the 500 levees throughout the county, many of which were designed 40 years ago. There are six major river watersheds in King County — the South Fork Skykomish, Snoqualmie, Sammamish, Cedar, Green and White — and since 1990 the county has been declared a flood disaster area seven times. Kitsap County experiences fewer floods than the other counties in the region, due to a lack of large river systems. Additional information on specific flood events that have occurred in the region, including data on the economic impact and disruption to the transportation system, is discussed in Section 4. Temperatures According to data from the National Weather Service, 2009 brought a record heat wave in the region in the month of July, as well as a cold snap in December with record cold temperatures. The average daily high in July is 75.1 degrees Fahrenheit, and in 2009 the average July temperatures reached 81.0 degrees, with an all-time record high reached on July 29, 2009 of 103 degrees. It was also the fourth -driest July on record. December 2009 also brought daily record lows, with temperatures reaching 16 degrees. On average, the temperature in December 2009 was approximately three degrees below normal. SECTION 3: SEA LEVEL RISE SCENARIOS Sea level rise is perhaps the most recognized and discussed potential impact from climate change. As part of this paper, PSRC used the projected sea level rise scenarios prepared by the UWCIG and Ecology and geographically mapped them to illustrate the potential impacts in the central Puget Sound region. The full methodology for this exercise is included in Appendix B of this paper, and was reviewed by Ecology and the Washington State Department of Transportation for consistency and reasonableness. A summary of the methodology is provided below, followed by the results of the mapping exercise in Exhibits 1-10. Sea Level Rise Estimates In January 2008, UWCIG and Ecology published local sea level rise estimates in the report, "Sea Level Rise in the Coastal Waters of Washington State." This report created sea level rise estimates for the Puget Sound, the Northwest Olympic Peninsula and the Central & Southern Coast. The estimates are based on 1) global estimates of sea level rise, 2) local vertical land movement and 3) local atmospheric circulation effects. 1) The global estimates were published in the IPCC's Fourth Assessment report, and are based on different emissions scenarios for 2050 and 2100. These estimates take into account the thermal expansion of the ocean and the melting of global ice (cryosphere). The extent of thermal expansion and cryospheric melting in the future depend on the level of continued contribution of greenhouse gases to the atmosphere. 2) The local vertical land movement estimates are derived from data gathered at gauges positioned around the state for over 100 years', and vary depending on the location in relation to the tectonic plates. The western areas of the state (the northwest Olympic Peninsula and the central and southern coasts) Verdonck, D, 2006: Contemporary vertical crustal deformation in Cascadia. Technophysics 417: 221-230. L-15 Appendix L: Climate Change Background