City of Irvine
2020 Local Hazard Mitigation Plan
with these pests. While the likelihood of a large outbreak is small within the City, the staff understands that the only effective mitigation is the removal of severely infected trees and managing and monitoring those that are still considered viable and managing the spread of the infestation.
Climate Change Considerations
Agricultural Pests Climate change is expected to modify the historical ranges of agricultural pests and place greater stresses on crops leading to higher susceptibility to future impact. Epidemic/ Pandemic/ Vector-Borne Disease Climate change generally will lead to the overall warming of the Southern California climate, which may cause insects, pests, and other vectors that carry disease to remain active for an extended part of the year. This possibility increases the threat of exposure to any infectious diseases that these pests carry. Additionally, vectors currently not active in Irvine and Southern California-at-large may migrate into the area as a result of warmer temperatures. Mosquitoes carrying West Nile Virus and Zika Virus would have an extended range. 57 Tree Mortality Tree Mortality is expected to increase under climate change conditions. Climate change will increase the likelihood of more severe and frequent episodes of drought, which could likely reduce the amount of water being used for irrigation for Irvine’s urban forest. When trees are under -irrigated, they become weaker and more vulnerable to infestation by pests. In this scenario, trees in Irvine would be more susceptible to infestation by ISHB, which could increase the overall mortality rate of trees in the City. 58
Drought
Description
A drought is a period in which water supplies become scarce. This can occur for a variety of reasons; in California, droughts occur when precipitation is limited for an extended period. Rain arrives in California via atmospheric rivers, channels of moist air located high in the atmosphere. When the atmospheric rivers bring less than usual moisture to California, it can reduce the overall amount of precipitation that falls on the state. Rain also comes to California as a result of the El Niño Southern Oscillation (ENSO) cycle, a regional meteorological phenomenon in the southern Pacific Ocean consisting of variations in the temperature of the ocean water and air. These variations give rise to two distinct phases known as El Niño , the warm and wet phase, or La Niña , the dry and cold phase. When the La Niña phase is active, it can cause California to receive lower than normal levels of precipitation. A drought may also occur when infrastructure connecting communities to long-distance water sources begin to fail. This can occur due to deferred maintenance or may be the result of a natural disaster. For example, many Southern California cities would experience drought conditions should the State Water Project or Colorado Aqueduct become severed during a powerful earthquake event.
Location and Extent
Given Irvine’s location, any drought that is significant enough to reduce water supply to southern California may have an impact on the City. However, City’s water supplies are provided by IRWD, which
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