The Floods Are Just the Beginning

The widespread floods that ravaged Northern California this winter have taken a terrible toll in damaged property, economic losses and disrupted lives. Unhappily, they may also provide a first glimpse of what lies in store for the state as the Earth’s climate heats up. Global warming is projected to produce an average temperature rise of only a few degrees over the next century, but that’s enough to cause dramatic effects. While it’s impossible to forecast exact changes in any local region, the challenges confronting Californians could prove difficult or impossible to manage.

Researchers project that water-related effects will be among the most severe. This winter’s floods mirror what could become the norm in a greenhouse climate. The major difference from this year’s events is that there would be less snow, with higher winter temperatures causing a reduction of total state snowpack by as much as 50%. More winter precipitation would instead fall as rain, and thus greater runoff and flooding would occur earlier in the season, as it has this year.

Less snowpack accumulation in the wet season means less water availability in the dry season, when it’s needed most. Spring and summer runoff would decline by 25% to 45% in different regions. Less dry season water, changing rainfall patterns and higher temperatures could also make droughts more intense and frequent. Historical conflicts over water can be expected to intensify.

The Sacramento/San Joaquin Delta, besieged by this year’s flooding, would face even greater threats. The delta is the linchpin of California’s water system, supplying two-thirds of the total state water supply and almost half the drinking water. Delta water quality could decline sharply, from increased salt-water intrusion caused by rising sea levels and increased pollutant concentrations due to lower flows of dry season runoff.

The heavily irrigated Central Valley--the heart of state agriculture--would be especially hard hit, since the delta also supplies 40% of the water for crops. Moreover, many crops are strongly affected by the timing of rains, variations in seasonal temperature and small differences between day and night temperatures--all of which will change unpredictably. Pests may increase in response to more favorable conditions. Increased yields for some crops in response to higher atmospheric carbon dioxide levels and a longer growing season cannot be expected to offset the negative impacts.

All this would be bad news for California’s economy. Agriculture, a major sector, accounted in 1994 for 8% of the gross state product and, directly or indirectly, one of every 12 jobs.

A warmer climate would affect California in other ways as well. Wildfires and forest fires are projected to be more severe and more frequent due to hotter summer temperature and drier conditions.

Forests would change and plant species in many ecosystems would be at risk. University of California researchers estimate that 20% to 50% of existing natural areas would no longer provide suitable habitat for species that currently thrive there.

Supplies of clean energy would tighten. Summer runoff ordinarily provides 20% of California’s electricity. With less runoff, less electricity would be available during the summer, the season for peak electricity demand.

Rising sea levels, caused by thermal expansion of seawater and melting polar ice, would lead to greater storm surge and flood damage along California’s densely populated coastal areas. Rising sea levels would also accelerate erosion of beaches and shoreline, destroying much of the scarce remaining wetlands that serve as critical habitat for many bird and marine species.

We cannot afford to be complacent about climate change. Humanity has unintentionally set in motion a planetary-scale experiment, but now we understand that the risks are far too great. It will take a coordinated international effort to curtail the impact we have on the Earth’s climate, and we must start now.