Climates

Just as California’s land mass was Pacific-born much the same is true for its climates, which are as diverse as its topographic features. Rainfall, temperature, and sunlight vary so significantly throughout the state that meteorologists speak of its micro-climates. Even within distinct geographical areas climates, especially temperatures, can fluctuate dramatically on a seasonal basis. Since the beginning of European settlement in California, climate has become increasingly important in shaping the state’s economy.

As elsewhere, California’s climates are influenced by many variables including wind patterns, ocean currents, and high-elevation mountains. The dominant weather pattern is for the westerly winds (precipitation-bearing onshore winds from the Pacific) to blow during the winter months, depositing rain - and in some places snow - from the northern to the southern end of the state. These somewhat warm winds have a swirling effect that draws colder ocean water to the surface, creating coastal fogs from the resulting air-moisture mix and condensation. Inland from the fog-shrouded coast, high-elevation mountains intercept the moisture carried by the prevailing westerlies while blocking their flow eastward. Hence the much drier and often arid weather east of the Coastal, Sierra Nevada, San Gabriel, and San Bernardino mountains.

The flow pattern of the westerlies is largely inoperative in the spring, summer, and early fall months when hot, dry winds blow from interior deserts toward the ocean. In southern California, for example, the Santa Ana winds often produce drought conditions, which, in turn, have resulted in hazardous fires. The Witch (Creek) fire in October 2007, for example, destroyed more than a thousand homes north and east of San Diego. Drought and Santa Ana wind gusts of up to 100 miles per hour forced the closure of many schools; the entire

Town of Julian was evacuated. Such wildfires have become more frequent and severe in recent decades.

Drought and wildfires occur throughout California despite the plentiful rainfall in the northern as compared to the southern part of the state. Temperatures rarely rise above 70 degrees Fahrenheit (F) in the northwestern corner of the state, where average annual rainfall exceeds 100 inches. The Mojave Desert in the southeastern part of the state represents the other end of the climate continuum. There temperatures can swing from below freezing in winter to summer highs above 120 degrees F. The average annual precipitation is 1.5 inches. In Furnace Creek, Death Valley, located in the Mojave, the American heat record was set on July 10, 1913, when the thermometer reached a hellish 136.4 degrees F! In what is billed as “the world’s toughest foot race,” athletes compete annually in the Badwater ultra-marathon, a grueling 135-mile run from Badwater, Death Valley to Mt. Whitney - from the lowest to the highest elevations in the 48 contiguous states. The race is held in mid-summer when Badwater temperatures reach a blistering 130 degrees F.

The most problematic and consequential aspect of California’s rainfall pattern is that three-fourths of the state’s water supply originates in the mountain snow packs in the northern third of the state while more than three-fourths of the demand comes from agriculture and the teeming population in the southern two-thirds. As a result, the state has constructed one of the world’s most extensive systems of aqueducts and dams to redistribute water to the otherwise parched farmlands in the Central and Imperial valleys as well as to Southland residents.

From this survey it is clear that there is no single California climate. Still, to the extent that there is a public image of such a climate, that image is based on the so-called Mediterranean weather conditions that prevail along the coastline from Santa Barbara to San Diego. The weather in this region is the most moderate in the state; summers are warm and dry and winters rarely get down to freezing while rainfall seldom exceeds 12 inches. This rare climate is found only in three parts of the world other than California and the Mediterranean Basin: central Chile, the Cape of South Africa, and southern and western Australia.

Such an ideal climate is marred principally by firestorms (already discussed) and smog. Smog (a term concocted from the words “smoke” and “fog”) is an unhealthy gray haze created when nitrous oxide, an air pollutant, reacts with sunlight to produce ozone. In the Los Angeles Basin the ozone is trapped by a combination of mountains, westerly winds, and temperature inversions. Instead of the ozone escaping into the atmosphere, which would happen under normal conditions, it is blocked by warmer air above it and sealed in the Basin by nearby mountains. Consequently, the ozone stagnates near ground level causing respiratory and other ailments among humans, and in the lower-elevation forests it slows tree growth, particularly that of the ponderosa pine. Smog has been a serious problem in southern California at least since the mid-twentieth century.

While air quality has suffered because of smog, the otherwise ideal Mediterranean climate in the Southland has spurred the regional economy. The movie and aircraft industries located in the region largely because of the weather. As a beach culture emerged in the twentieth century, bathing suits and other ocean-oriented apparel gave rise to a very profitable sportswear enterprise.