City of Irvine
2020 Local Hazard Mitigation Plan
Climate Change Considerations
Fault Rupture Generally, there is no known direct connection between fault rupturing and climate change. Some evidence suggests that greater oceanic pressure on tectonic plates as a result of melting land ice could influence the behavior of seismic events, but there is little to indicate that this would play a major factor in any seismic event, including fault rupturing. Liquefaction Climate change is anticipated to change the usual precipitation patterns in Southern California. Periods of both rain and drought are anticipated to become more intense and frequent. This means that more precipitation will likely occur during rainy periods, and drought is expected to last even longer. As a result, the groundwater aquifer beneath Irvine and Orange County as a whole could rise during intense periods of precipitation, but, alternatively, longer-lasting drought may lead to more groundwater withdrawal and could lower groundwater elevations. Therefore, climate change could, depending on the circumstances, either increase or decrease the future risk of liquefaction in Irvine. Seismic shaking There is no direct link between climate change and seismic activity that could impact Irvine, so climate change is not expected to cause any changes to the frequency or intensity of seismic shaking. Some research indicates that climate change could result in “isostatic rebounds,” or a sudden upward movement of the crust as a result of reduced downward weight caused by glaciers. As glaciers are known to melt when overall global temperatures increase, climate change could indirectly lead to an increase in seismicity in Southern California. 95
Severe Weather (Extreme Heat, Severe Wind, Rain)
Description
Extreme Heat Extreme heat is a period when temperatures are abnormally high relative to a designated location’s normal temperature range. There are generally three types of extreme heat events: 96 • Extreme Heat Days: a day during which the maximum temperature surpasses 98 percent of all historic high temperatures for the area, using the time between April and October from 1961 to 1990 as the baseline. • Warm Nights: a day between April to October when the minimum temperature exceeds 98 percent of all historic minimum daytime temperatures observed between 1961 to 1990. • Extreme Heat Waves: a successive series of extreme heat days and warm nights where extreme temperatures do not abate. While no universally accepted minimum length of time for a heatwave event exists, Cal-Adapt considers four, successive extreme heat days and warm nights to be the minimum threshold for an extreme heatwave. Extreme heat events will feel different from region to region since different areas have different historic high temperatures. For example, an extreme heat day on the coast will feel different than an extreme heat day in the High Desert. The reason for this is how humidity plays a factor in the perceived heat that
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