The assessment said Californians can expect more heat and more extreme weather, which would lead to more wildfires, floods, drought and public health issues. California’s Fourth Climate Change Assessment was produced as part of a volunteer initiative by climate experts. The assessment updates the third one issued in 2012.
The researchers used tools, including the Coastal Storm Modeling System, which makes detailed predictions of coastal flooding, erosion and cliff failures; Cal-Adapt, a portal for climate projections produced for the assessment; and Cal-Heat, a new tool for the assessment that informs local public health officials’ initiatives to protect the public during heat events.
Though the models predict a hotter, drier California, that doesn’t mean you have to look into the future to see the effects of climate change, according to contributing author Jay Lund. “We’re already starting to see some of the effects of the warmer climate from the hydrology,” he said. “We’ve been seeing roughly 1 percent of average runoff coming more in the winter than in the spring.”
That squares with future calculations of the state losing a good majority of the snowpack as precipitation falls in the form of rain instead, leading to more flooding and drier summers. “You can have a very warm flood,” Lund said. “The atmosphere is going to come in with more moisture and hit that big wall of the Sierras [Sierra Nevada] and drop a lot of moisture.”
Projections from the assessment suggest that the state water supply from snowpack will decline by two-thirds by 2050, and if action isn’t taken in the form of reduced emissions, water from the snowpack could be reduced to a third of historical levels by 2100.
There will be much greater variability in precipitation. In the warmer climate, the atmosphere will hold more moisture and some of the storms will be wetter. “Because the Earth is warmer and there’s a more energetic atmosphere, there will be more variability in the annual quantities of water, meaning bigger droughts and bigger floods, even if the average is the same,” Lund said.
The California Department of Forestry and Fire Protection already considers fire season to be year-round as conditions have worsened, and that is only expected to intensify. One study used for the assessment suggests that if greenhouse gas emissions aren’t curbed that “the frequency of extreme wildfires burning over approximately 25,000 acres would increase by nearly 50 percent,” according to the assessment.
The assessment recommends reducing tree density and restoring beneficial fire to improve long-term resilience.
Sea-level rise is another issue raised in the assessment, which projects that “under mid-to-high sea-level scenarios, 31 to 67 percent of Southern California beaches may completely erode by 2100 without large-scale interventions.” The Hazardous Exposure Reporting and Analysis tool is a coastal evolution model aided by the assessment that provides information about the number of residents affected by sea-level rise.
Climate change will also affect public health. Heat waves are the natural disaster responsible for more deaths in California over the last 30 years. The heat wave of 2006 killed more than 600 people and sent 16,000 to the emergency room. The assessment suggests mortality risk for those over 65 would increase tenfold by 2090.
Lund said new technologies can become part of an overall solution. “You’ll probably see changes in the way we do air conditioning, the way we manage energy systems, some of the water systems, the public utilities, the way we alert public health officials to individuals who might be susceptible to heat waves. Technology will help with some of these problems.”
