Rep. Henry Waxman, D-Los Angeles, the ranking member of the House Committee on Energy and Commerce, asked the Sierra Nevada Research Institute at UC Merced a series of questions about the effects of climate change on California as background for policy development. The following are some of the responses from Sierra Nevada Research Institute director Roger Bales and senior researcher Norm Miller.
What are the most serious threats facing Northern California because of climate change?
Northern California, in particular northeastern California, is projected to have increased warming with early snowmelt and runoff. It is very likely that there will be more intense winter storm events impacting both inland and coastal regions, and it is very likely that there will be flooding during these events. Perturbations to our water supply will stress both infrastructure and decision-making capabilities.
What are the most serious threats facing Southern California because of climate change?
While Southern California is also expected to receive intense precipitation events during the winter, it is very likely to have an overall reduction in precipitation. The most serious threat due to climate change is a decrease in fresh water and an increase in intense wildfires.
Sea level rise will impact port infrastructure, as adjustments to docks, jetties, and other fixed platforms will need to be altered. The Central Valley Project and the State Water Project pumping plants are at risk of failure if flooded.
How will climate change affect precipitation and water availability in California?
Precipitation modeling has large uncertainties; however, a fairly robust signal across models indicates that Northern California will receive an increase in intense precipitation events during the winter and Southern California very likely will have a decrease. The annual cumulative amount of precipitation is likely to be about the same, but very likely a redistribution with intense precipitation periods alternated with very dry years.
Overall, California is likely to experience 50 percent to 150 percent more critically dry years. Water availability is certain to be more variable, as observations indicate California precipitation is becoming more and more variable. It is likely that a multiyear drought will occur, as has occurred numerous times in the past; however, future droughts may be longer lasting.
The shift from snow to rain in the Sierra Nevada, decreased snow cover area, coupled with longer growing seasons, are certain to result in more winter stream flow and less summer stream flow, impacting water deliveries during the growing season. This loss of snowpack storage will reduce water security for California.
How will rising sea levels affect coastal communities?
Coastal communities will be impacted with higher storm surge events resulting in flooding. Major cities, including San Francisco, San Diego and Los Angeles are at risk of flooding. The San Francisco Bay and Delta are at high risk for flooding during combine intense precipitation, sea level rise and storm surge.
To what extent will climate change increase the frequency and severity of heat waves in California?
Analysis of climate observations and models indicate that present-day heat waves, multiple days with temperatures in the top 5 percent of historic warmest days, will increase by two to four times the current level. By midcentury, California temperature increases are very likely to range between 2 degrees and 5 degrees, with end-of-century increases of 3 degrees to 10 degrees.
Heat waves may occur anywhere in the state, but it is important to note that high population density regions, people who lack sufficient cooling, elderly people and children are most at risk. Parts of the Central Valley, where temperatures may soar beyond 110 degrees, as experienced in Sacramento for two weeks in 2005, may become annual occurrences. This is likely to have a major impact on agricultural workers and others in the Central Valley.
To what extent will climate change increase the frequency and severity of wildfires in California?
Naturally occurring wildfires are very likely to be larger in extent due to increased drying of fuel load during the summer season.
What impact will climate change have on agriculture in California?
Crops that are not water-efficient (e.g. rice, cotton) are very likely to be replaced with more water-efficient crops. Crops that are sensitive to extreme heat periods will have low productivity years, impacting the state's overall economics. Many Central Valley specialty crops, which are the foundation of the agricultural economy, are especially vulnerable to higher nighttime temperatures.
How will climate change affect the Sacramento-San Joaquin Delta?
The Delta receives flows from Northern and Southern California Sierra watersheds, and during intense precipitation reservoirs have released water to protect the integrity of infrastructure. With an expected increase in intense precipitation, especially in the northern region, release of water will occur more frequently, impacting hydropower, agriculture and ecosystems. It is very likely that the timing of runoff will be earlier and Southern California water allocations, especially for agriculture, will be impacted. Sea-level rise is a real threat to both Delta ecosystems and the transfer of freshwater from the Sacramento River through the Delta to pumps for the California Aqueduct.
Is it reasonable to expect that climate change could harm California's economic competitiveness?
Tourism may be affected due to impacts in the Sierra ski industry. Agriculture may require a shift away from water-inefficient crops, causing price changes. How we manage our water in a warmer climate will depend on having appropriate institutions, infrastructure and information; water is central to maintaining economic output and competitiveness.