Everything I Used to Know About California’s Climate (And Wish I Could Remember)

Climate is an important and timely topic, but it has probably been a while since you took a climate class. This article is a brief refresher course on California’s climate that will help shake out the cobwebs in your brain and prepare you to pass the California Supplemental Exam for landscape architects.

Here are some climate basics to get stimulate the climate department of the brain.

Before we start discussing climate and microclimate and how they affect the site inventory process, let’s first define what climate is.

What is Climate?

According to Wikipedia, climate “encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods”.

Climate is Different than Weather

Weather is the present condition of all the climate elements and their variations over a short period of time. Climate is defined as a location’s average weather over a period of 30 years.

What Factors Determine A Region’s Climate?

“The climate of a location is affected by its latitude, terrain, and altitude, as well as nearby water bodies and their currents. Climates can be classified according to the average and the typical ranges of different variables, most commonly temperature and precipitation.” (Source: Wikipedia)

California’s diverse climates are generated by the climate system. The climate system model has five components:

  • Atmosphere
  • Hydrosphere
  • Cryosphere
  • Land Surface
  • Biosphere


The Earth’s atmosphere is a layer of gases that surround the planet. The atmosphere protects and sustains plant and animal life by providing oxygen and absorbing ultraviolet solar radiation which warms the planet’s surface through heat retention. In addition, the atmosphere moderates the planet’s temperature and buffers extreme diurnal temperature variations. Air contains approximately 78% nitrogen, 21% oxygen, 1% argon, 0.04% carbon dioxide, and small amounts of other gases. Water vapor is also found in air in varying percentages. The relative amount of water in the air is referred as humidity.


The hydrosphere is the combined mass of water found on, under, and over the surface of a Earth. You likely remember from studying the water cycle that most of the planet’s water is tied up in the oceans. A particular site’s climate is affected by its proximity to water bodies (i.e. the ocean, rivers, etc.).

Graphic of the Water Cycle

The Water Cycle. Graphic courtesy of the USGS.


“The cryosphere is the term which collectively describes the portions of the Earth’s surface where water is in solid form, including sea ice, lake ice, river ice, snow cover, glaciers, ice caps and ice sheets, and frozen ground (which includes permafrost). Thus there is a wide overlap with the hydrosphere. The cryosphere is an integral part of the global climate system with important linkages and feedbacks generated through its influence on surface energy and moisture fluxes, clouds, precipitation, hydrology, atmospheric and oceanic circulation. Through these feedback processes, the cryosphere plays a significant role in global climate and in climate model response to global change.” (Source: Wikipedia)

The cryosphere has less influence on some parts of California than others due to elevation and latitude. While much of California’s land mass remains unfrozen for much of the year, there are still a few glaciers in the state.

Land Surface

Land surface has an impact on a region’s climate. A report from a climate think-tank found “soil moisture is shown to be responsible for modulating the surface-atmosphere interaction at a continental scale, on time scales ranging from the diurnal to the seasonal.” Another way that the land surface affects a regions climate is through albedo which is the reflection of energy from the Earth’s surface. Deserts typically reflect more energy back into the atmosphere than more temperate and lushly vegetated areas.


The biosphere has been defined as “…the global sum of all ecosystems.” Plants and other living organisms in various biomes can affect the area’s climate. For example, plants take up and release water and and cast shadows which reduces the amount of energy reflected back into the atmosphere. While biomes are largely determined by climate, biomes interaction with climate helps buffer the biome from climate changes by preserving its local climate system.

What Climate Types Are Found in California?

California’s climate varies from arid to subarctic depending on latitude, elevation, and proximity to the coast.

The Coast
Coastal and southern parts of the state have a Mediterranean climate, with somewhat rainy winters and dry summers.

Further inland, the climate becomes more continental, with some areas turning semi-arid, with colder winters and markedly hotter summers.

The Valleys
Low-lying inland valleys, especially the Central Valley, have a hot Mediterranean climate, with subtropical temperatures but a well-defined summer dry season and cool, foggy, rainy season.

The location of mountains determines the location of deserts because of the rain shadow effect. You can find desert climate regions in California that lie east of the high Sierra Nevada mountains and Southern California’s Transverse Ranges and Peninsular Ranges.

California has several different desert climates.

High Desert
The higher elevation deserts of eastern California, including the Mojave Desert, Owens Valley, and the Modoc Plateau, are part of the Great Basin region which extends through higher elevation desert areas of the Four Corner states.

Southeastern regions of California have a hot arid desert climate which is similar to the Sahara Desert in norther Africa. The northern portion of the Mojave Desert on the east side of the state has Death Valley which is one of the hottest places in the United States. Winters are cold with occasional snow. Summer monsoons ocassionally bring torrential downpours and flash floods

Low Desert
Eastern southern California’s low deserts, including the Coachella and Imperial valleys and the lower Colorado River, are part of the Sonoran Desert. The Sonoran Desert extends eastward into Arizona and south into Sonora, Mexico. Sonoran Desert areas are known for their hot summers and nearly frostless mild winters. Monsoon season arrives in late June and extends through early September and which draws moisture from the tropical Pacific, Gulf of California, or Gulf of Mexico into the deserts. Summer moisture supports a greater diversity of lifeforms than higher deserts

The Mountains
Mountains are common in the eastern part of the state. High mountain ranges, including the Sierra Nevada, the Cascade Range, and the Klamath Mountains, have a mountain climate with snow in winter and mild to moderate heat in summer.

Coastal Influence

The influence of the ocean generally moderates temperature extremes, creating warmer winters and substantially cooler summers, especially along the coastal areas.

The cool California Current offshore, enhanced by upwelling of cold sub-surface waters, often creates summer fog near the coast, creating a moderate oceanic climate on the northern coast and a moderate Mediterranean climate from about Cape Mendocino southward.

Coastal areas are about 7° F warmer during the winter than inland valley areas. However, inland valleys are approximately 25° F (14 °C) warmer during the summer.

While the above generalization are usually true, the Palm Springs and Coachella Valley are the exception. During the cool winter months, these valleys regularly have the warmest temperatures in the western United States.

Summer temperatures rise one or more degrees F for each mile inland from the ocean. This explains why the city of Burbank, which is only 10 or so mile from the coast, is much warmer than Santa Monica beach.

Unique Climate, Unique Place

California’s climates are diverse and influenced by a number of factors. As a result, California supports an abundance of biodiversity and natural beauty.

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John is a landscape architect who is currently preparing to take the California Supplemental Exam to become licensed in California. He is currently a licensed professional landscape architect in Georgia and Florida. John graduated from California State University, Pomona with a BSLA degree in landscape architecture in 1997 and has extensive practice experience in residential and commercial landscape design.

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