Geoscience Reference
In-Depth Information
the links between the larger-scale atmospheric circulation over the Sierra
Nevada and the hydrology in those mountains. For instance, the amount of
silica dissolved in the water provides information about chemical weather-
ing (dissolution) of rocks and minerals in the watershed, and nitrate and
nitrite concentrations rel ect pollution levels in the atmosphere. Among
other results, these studies reveal that the spring snowmelt has indeed been
starting earlier.
Earlier snowmelt has propagated impacts downstream as well, such as on
water quality and ecosystems in the San Francisco Bay. Monthly monitoring
ef orts in the bay by the U.S. Geological Survey over decades have shown that
earlier snowmelt is causing the salinity of bay waters to rise during the late
spring and summer.
Wildi res on the Rise
As the mountain slopes across the great mountain ranges of the West dry,
their forests—the pine, Sequoia, and juniper—will be increasingly suscep-
tible to insect infestations, disease, and, inevitably, i re. Diminished winter
snowpack, earlier spring snowmelt, and longer, hotter summers will weaken
the entire forest ecosystem, leaving the trees fragile and l ammable, increas-
ing the number of forest i res across the West.
Residents of the West are all too familiar with this lethal ef ect of warm-
ing and drying. For instance, Southern California residents experienced
a catastrophic i re season in 2007 in which close to a million people were
evacuated and two thousand homes were destroyed, resulting in $1 billion
in damages. For the climatologists at Scripps, this i re season was a painful
reminder of the precarious conditions of life in the West. h e region had suf-
fered from a lack of adequate precipitation for seven years, including a deep
drought in early 2007. Weakened by the dry conditions, millions of acres of
spruce, piñon, and ponderosa pine succumbed to bark beetle disease, leaving
vast stands of dead trees across the region that acted as kindling during the
summer heat waves (see i gure 33).
h e following year, over two thousand wildi res raged throughout the
state of California, scorching 900,000 acres. Subsequently, during the fall
of 2008, communities in Los Angeles and Santa Barbara were scorched as
hurricane-strength winds roared through the region.
h e 2007 and 2008 i res were devastating, but were they a sign of a system
out of balance? At er all, i re has been a natural phenomenon in California
