Southern California: Geography, Climate, and Ecological Communities

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Southern California Geography, Climate, and
Ecological Communities
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Southern California

• over 50 of CA population
• 1/6 of states land area
• Greatest concentration of unique species in CA
• greatest endangered species in continental U.S.

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Geography of Southern California

• Transverse ranges
• Santa Monica, San Gabriel, San Bernardino
  Mountains
• Peninsular ranges
• Santa Ana, San Jacinto, Laguna Mtns.
• Valleys
• San Fernando, San Gabriel, Santa Ana
• Rivers
• Los Angeles, San Gabriel, Santa Ana

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Southern California Climate

• Caused by
• Cold California current
• 34 deg. N latitude
• Combination of...
• Mediterranean Climate
• Long hot summers
• moderate winter precipitation
• Maritime Influence
• Gives a marine layer and a temperature inversion
  layer

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The Climate of Southern California

• Annual precipitation
• Variable from year to year, L.A. ave. 15
• Increases with elevation
• Decreases from north to south
• Decreases with distance from ocean
• Most falls in winter months
• Temperature
• Moderate year-round
• average high 75 F
• average low 57 F

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Weather in L.A.

• marine layer in summer months (May-Aug)
• marine layer
• Rainy season NovemberApril
• Pacific storms push cold fronts across California
  
• 92 of our rainfall
• rainy season storms alternate with dry periods
• 10-30 individual storms per season
• Snow at high elevations
• Current weather image

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Weather in L.A. the Wet Season in Winter

• Rainy season November--April
• Eastern Pacific high pressure ridge displaced to
  south
• When cold air is aloft, marine layer breaks down
• Lets Pacific storms push cold fronts across
  California
• 92 of our rainfall
• rainy season storms alternate with dry periods
• 10-30 individual storms per season
• Snow at high elevations
• Current weather image

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Winter Storms in Southern California

• 1900-1943
• many storms hit S.California
• about same frequency as rest of state
• led to flood control measures (river
  channelization)
• 1943-1992
• extreme rainfalls only 5 times (14 statewide)
• BUT heavy rainfalls in 90s (92, 93, 95, 97,
  98)
• wettest decade since 1930s, 1940s

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• Most rain in 1 day
• 26.12 inches on slopes of Mount Wilson
• January 23, 1943
• Other big storms
• 2.60 in 1hr
• 1/4/95 in Long Beach
• 0.65 in 1 min.
• 4/3/26, north of Mount Wilson

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Temperature change with distance from coast
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Santa Ana Winds
Bel Mar Fire, Santa Monica Mountains, 6/98.
Photo USFS
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Southern California Seasons
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Classification of Biological Communities

• California Communities
• Extreme range of climate and vegetation
• System devised by Munz and Keck in 1959 and is
  still in use
• Based on dominant plant species in each area
• Examples Joshua Tree Woodland and the Coastal
  Redwood Forest

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Southern California Communities

• Coastal Sage Scrub
• Chaparral
• Riparian Woodland
• Oak Woodland
• Montane forest
• Alpine tundra

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Biotic Zonation in Southern California
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Riparian Woodland
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