Environmental Health Center
The good news was that the damage could have been worse. Because forecasters predicted this El Niño months ahead of time, state and federal officials had time to prepare. Sandbags were rarely in short supply.
California also suffered during the five-year grip of a drought in 1987-92. It stretched the state's water reserves past their limits and cost farmers hundreds of millions. Too little water was as bad as too much.
Those two events offered California a reminder -- perhaps a wake-up call -- of its continuing vulnerability to climate variability and weather extremes. As the prospect of global greenhouse warming grows more certain, both the deluge and the drought stand as examples of what California might face during the 21st century.
Weather is already varied and changeable in California. The lethal heat of Death Valley is as Californian as the snow atop the Sierras. Natural cycles like "El Niño Southern Oscillation" (a warming of the surface layer of the tropical Pacific that recurs on roughly a 2- to 7-year cycle and causes wild swings in weather across much of the globe) already do push weather to extremes. Now it appears that global warming caused by human activities could push California weather to still further extremes.
This paper outlines some of the potential impacts of climate variability and change on California. It doesn't try to predict "what will happen." But it does try to point to the special ways California is vulnerable to weather extremes - as well as the special opportunities changing weather may present.
The problem is that human activities have been increasing the atmospheric concentrations of "natural" greenhouse gases and adding some new man-made ones, such as the chlorofluorocarbons. Simple physics suggests that this will warm the earth. But the climate system is huge and complex, and that makes it hard to predict exactly how much warming will happen, when it will happen, and how it will affect weather patterns.
The best current predictive tools, however imprecise, are computer "models" that simulate the global climate system. Scientists do not yet claim much reliability for computer projections of climate change at scales as small as a single U.S. state. But scientists and models do tend to agree on general projections for a given continent and a given latitude. What do the models say?
California will be warmer and wetter, if greenhouse gases change global climate as expected. By the year 2100, temperatures in California could rise by about 5ºF and precipitation could increase by 20-30% if warming goes unchecked, according to EPA and the IPCC.
Those numbers are merely best estimates, from the Hadley Centre climate model in the UK. The estimated temperature increase could be anywhere from 2 to 9ºF in the winter and a bit less in the spring and fall. Precipitation could increase anywhere from 10% to 50% in the spring and fall, with larger increases during the winter, California's wet season. Results would vary starkly from place to place; the National Weather Service defines seven climate regions in California, ranging from the hot, arid desert of the to the cool, rainy forests of the Northwest.
If global warming continues, by 2100 sea level could rise 13 to 19 inches beyond what it would otherwise. As the oceans slowly warm, they will expand, and melting polar icecaps will add more water.
Little is known about how the warming of global climate would affect the other cycles driving California weather. The best known is the El Niño. During El Niño years, California gets heavier rainfall than average, especially in the winter. Sometimes the ENSO pendulum swings into an opposite phase called La Niña, when the tropical Pacific surface cools. During La Niña years, Southern California tends to get drier-than-average weather, while Northwest California tends to get wetter-than-average weather.
"Average" weather is not something California gets very often. Drought and floods are common in many parts of the state, even during years not marked by either a warm phase or a cold phase of ENSO. So it seems that there are other forces besides ENSO bringing extreme weather to California, some of them not understood. Scientists are only beginning to understand multi-year climate cycles such as the Pacific Decadal Oscillation, which also affects California.
Most of the water is shipped to the places that need it through a network of aqueducts, canals, and reservoirs - one of the largest in the world. The two major sources of water for the arid regions are the Colorado River and the Sierra Nevada mountain range. Snow that falls on the Sierras and the Rocky Mountain headwaters of the Colorado melts in the spring and is captured in reservoirs.
Despite the dams and reservoirs for catching water, flooding has been a serious and recurring problem in parts of California, such as the Kern River watershed in the Central Valley. When snowpack is heavy, or spring's melt sudden or early, or rainfall heavy, the dams must spill water. Climate change is likely to affect not only the overall amount of water California receives, but also the timing, form (rain or snow), and location of it - which directly affect people. If more precipitation falls as rain instead of snow (as is expected), the result would be more runoff during the wet winter season (when floods occur) and lower streamflow during the summer, when it is most needed.
The sea level rise expected to accompany global warming can cause salt water to intrude into coastal aquifers, making it useless for drinking or irrigation.
To accomplish this miracle of productivity, Californians have changed much of the state's landscape, reclaiming what was once considered "desert" and making it into productive farmland with irrigation. More than 80 percent of the state's cropland is irrigated. California's farms are heavily dependent on managed water. Changes in the frequency or severity of drought and flooding, a possible but uncertain consequence of climate change, could have a huge economic impact on California agriculture.
The effects of climate change on California farms could go well beyond water. Warmer weather can in some cases spur crop growth, though in other cases it can be detrimental. Shifts in seasonal timing or local temperature ranges could make growth of some current crops unfeasible, while bringing opportunities for new crops as well. The increased carbon dioxide in the atmosphere may actually improve plant growth in many cases. But changes in temperature and humidity may also affect agricultural pests - possibly suppressing some, but also likely to increase others, since many insects and fungi like warmer, wetter weather.
Climate change is generally expected to shift northward (or upland) the suitable range for particular ecosystems throughout the Northern Hemisphere. How that shift plays out in any particular sub-region of California could vary. Problems could arise if natural barriers or human development block the northward migration of species, or if climate changes more rapidly than species can migrate. Such migration has already been observed with one California butterfly species, the Edith's Checkerspot. Fruit and nut plants, an improtant part of the economy can take decades to establish.
Decreased summer streamflow would increase the salinity of San Francisco Bay and the San Joaquin Delta, kicking off a complex sequence of changes in ecosystems serving as a major breeding and feeding ground for invertebrates, fish, birds, and other species.
Changes in ocean currents, which climate change could also bring, would bring changes to marine communities. The California Current has warmed in recent decades, although scientists do not know whether the warming is caused by natural variability or manmade greenhouse warming. This has led to a reduction in zooplankton, a basic building block in the marine food chain. Certain coldwater species, such as the sooty shearwater and greenspotted rockfish, have declined, while other, warmwater species, such as Garibaldi, have increased in numbers or moved north.
These are only a few examples of the kind of ecological change that global climate warming could bring to California.
Wildfire is closely linked to weather and climate. During wet years, flourishing plant growth builds up fuel. Then when a hot and dry period comes along, the dead or dry fuel becomes more combustible, and fires start easily. When hot, dry weather is combined with high winds - as it is with the Santa Ana winds of Southern California - the fire potential is even more explosive.
The rain-fire cycle predates human settlement , but manmade greenhouse warming could change vegetation and weather patterns in ways that could make fire patterns worse. Regardless of whether it is wetter or drier, the continued variation in year-to-year precipitation will likely lead to increases in fires as fuel loads increase in wet years and burn in dry years.
Landslides are another of those perennial "disasters" that seem to make the news almost every year in California. Extremely wet weather is one of the root causes of landslides, and California's weather is likely to be wetter (and possibly more extreme) in a greenhouse world. California has certain land forms that are especially susceptible to landslides - most visibly the coastal bluffs and mountains. In some cases, human-caused fires, erosion, and vegetation changes make landslides more likely. Often people locate residences and other buildings in scenic areas where land is unstable. Sea-level rise could open coastal bluffs to erosion which will only make landslides worse.
| June 23, 2000 | | Disclaimer/Policy |
