Climatic Factors in California
Factor
Latitude
Effect on Temperature
Effect on Precipitation
Elevation
Mountain Ranges/Rain
Shadow Effect
Nearness to the Ocean
On the back of this paper, draw a label a picture of the Rain Shadow Effect. Make
sure to include details so that you can remember and explain how it works.
Climatic Factors in California
California has greater climatic diversity than any other state, and its vegetational diversity is
reflective of this varied climate. For example, California has climatic regions in the northwest
that receive over 100 inches of precipitation per year and support temperate rain forests. IN
contrast, some arid regions in the southeastern portion of the state get less than 2 inches per
year and are among the hottest, driest deserts in the world (Death Valley). California has
areas along the coast that seldom, if ever, are exposed to freezing temperatures and areas on
the peaks of high mountains that can experience front any day of the year. Locations only a
few miles apart may have enormously different environments. For example, areas along the
immediate coast like Bodega Bay and Fort Brag have mild summer temperatures. High
temperatures average between the 60s and 70s. Just a few miles inland in Windsor or Ukiah,
summer temperatures average in the 90s and are often over 100 F.
California’s regional climates are mostly a result of its extremely diverse topography, its wide
range of elevations, its wide range in latitude (32.5 to 42 north) and its proximity to the
ocean.
Latitude
As a general rule, temperatures decrease and precipitation increases from southern to
northern California. Vegetation responds to these climatic trends. In the areas around San
Diego grasses and coastal scrub predominate along the coast. As you travel northward along
the coast, the vegetation gradually changes form coastal scrub through coastal live oak
woodland and various other communities to coastal redwoods and northern coniferous
forests around Eureka and Crescent City.
Elevation
Precipitation generally increases with elevation. Moist marine air masses are carried by
westerly winds over the western slopes of the California Mountains. As this air rises over the
mountains, it cools, reducing the air’s ability to hold water vapor, which condenses, and falls
as precipitation mostly on the western slopes. The highest precipitation usually corresponds
with upper montane coniferous forests (4000-7000 ft). Above this elevation, precipitation
decreases because most of the water has already fallen at lower elevations.
Mountains tend to create “rain shadows”. An air mass that has passed over a mountain heats
up as it descends in elevation down into valleys. As the air warms, its moisture holding
capacity increases, and it can absorb more moisture from the land and from plants living
there (evaporation). Consequently, there is much less precipitation and the climate is drier on
lee slopes of a mountain chain than on the windward slopes. Because storms in California
move from west to east from the Pacific Ocean, rain shadows occur to the east of the
mountains. The deserts of the state are all on the lee side of one or more mountain ranges.
The Central Valley of California is in the rain shadow of the Coast Ranges. Taller mountains
tend to cast a more dramatic rain shadow. For example, the Cascade and Sierra Nevada
ranges block moisture from about one third of the United States! Death Valley is in the rain
shadow of two tall mountain ranges: the Sierra Nevada and the Panamint Range.
Ocean Influence
Along the immediate coast of California, the climate is cool and mild and does not display
much daily or seasonal temperature fluctuation. The ocean serves as a giant heat reservoir.
The ocean moderates the temperature of air masses passing over it by absorbing heat in the
summer and releasing heat in the winter. Consequently, the air temperature of areas along
the coast is generally cooler than inland areas in the summer and warmer during the winter.
Climates that are influenced by the ocean are called “maritime” climates.
Inland from the ocean’s influence are “continental” climates. Hot dry summers and cold
winters characterize the continental climates of the Central Valley and nearby foothills.
Montane climates are found at high elevations in the Sierra Nevada and other interior
mountain ranges. These climates are more similar to the continental climates in the central
portions of the United States where the winters are harsh and most of the winter
precipitation falls as snow. Both continental and montane climates have distinct seasons and
show much greater daily and seasonal temperature fluctuations than do maritime climates.