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CHAPTER 6. IDENTIFIED HAZARDS OF CONCERN AND RISK ASSESSMENT METHODOLOGY <br />6-2 <br />6.2. CLIMATE CHANGE <br />Climate includes patterns of temperature, precipitation, humidity, wind and seasons. Climate plays a <br />fundamental role in shaping natural ecosystems, and the human economies and cultures that depend on <br />them. “Climate change” refers to changes over a long period of time. Climate change will have a measurable <br />impact on the occurrence and severity of natural hazards around the world. Impacts include the following: <br />• Snow cover losses will continue, and declining snowpack will affect snow-dependent water <br />supplies and stream flow levels around the world. <br />• The risk of drought and the frequency, intensity, and duration of heat waves are expected to <br />increase. <br />• More extreme precipitation is likely, increasing the risk of flooding. <br />• The world’s average temperature is expected to increase. <br />Climate change will affect communities in a variety of ways. Impacts could include an increased risk for <br />extreme events such as drought, storms, flooding, and forest fires; more heat-related stress; and the spread <br />of existing or new vector-born disease into a community. In many cases, communities are already facing <br />these problems to some degree. Climate change changes the frequency, intensity, extent, and/or magnitude <br />of the problems. <br />According to the Dalton et. al. report “Climate Change in the Northwest,” temperature and precipitation <br />extremes in the Northwest will increase. In the period averaged over 2041 to 2070 there will be more days <br />above maximum temperature thresholds and fewer days below minimum temperature thresholds compared <br />with the 1971–2000 average. For example, the number of days greater than 32 °C (90 °F) increases by 8 <br />days (± 7), and the number of days below freezing decreases by 35 days (± 6). The number of days with <br />greater than 1 in (2.5 cm) of precipitation is projected to increase by 13% (± 7%) and the 20-year and 50- <br />year return period extreme precipitation events are projected to increase 10% (-4 to +22%) and 13% (-5 to <br />+28%), respectively, by mid-century. <br />According to the US Environmental Protection Agency (EPA), the Northwestern US has experienced <br />warming temperatures and declines in snowpack and streamflow in recent decades. Average annual <br />temperatures have risen by about 1.3 degrees Fahrenheit over the last century, and are expected to increase <br />by 3 to 10 degrees Fahrenheit by the end of this century. Summer precipitation is projected to decline by as <br />much as 30%, with less frequent but heavier downpours. Declines in snowpack will reduce the amount of <br />spring snowmelt that replenishes streams and rivers, which may impact water supply in a season with very <br />little rainfall. Changes in streamflow will have impacts on agriculture, hydropower, municipal and <br />industrial uses, and protection of ecosystems. Due to earlier peak streamflow, summer hydropower <br />generation is projected to decline, but winter hydropower gener ation may increase. Rising temperatures, <br />combined with changing precipitation patterns, are resulting in reduced soil moisture. This makes forested <br />areas increasingly susceptible to wildfires, insect outbreaks, and disease. An increase in the number and <br />size of wildfires has been observed in recent decades, and is expected to worsen in future years. These <br />changes will have cascading impacts on ecosystems, as well as the timber and bioenergy markets. <br />This hazard mitigation plan addresses climate change as a secondary impact for each identified hazard of <br />concern. Each chapter addressing one of the hazards of concern includes a section with a qualitative <br />discussion on the probable impacts of climate change for that hazard.