Climate of the Desert Areas of Southern California

HIGH ELEVATION AREAS

Elevation: generally 4000 to 6000 feet

Precipitation: 4 to 14 inches per year

Average Temperature Range (in degrees F)

Summer: High 85 to 100 / Low 50 to 65

Fall: High 60 to 85 / Low 30 to 55

Winter: High 40 to 60 / Low 20 to 40

Spring: High 50 to 85 / Low 30 to 55

Maximum Sumer Temps: 95 to 105

Minimum Winter Temps: 5 to 20

Area: This zone includes all the desert mountains within the Mojave Desert’s basin & range topography. The dry leeward slopes of the larger mountain ranges like the San Bernardino, San Gabriel, Tehachapi, Eastern Sierra, & San Jacinto Mountains are have this climate. Cities in this zone include Lone Pine, Summit Valley, Bishop, & parts of Phelan. In general, areas higher than 6000’ have a cooler moister mountain climate. Some areas like Pioneertown & Oak Hills are in transition zones to either warmer or colder areas.

Climate Characteristics: From late autumn into the middle part of spring cool to cold weather dominates. In winter pacific storms visit providing rain & snow. These pacific storms also bring cold & strong winds. Hard freezes are common during the winter especially on clear windless nights. Spring is a short transitional season between winter & summer. Spring weather is notoriously unpredictable & variable. Frost can occur late in the year & heat waves can occur early in the spring. For the most part spring weather is sunny breezy to windy with mild to warm days & cool to cold nights. Summertime weather is usually sunny, breezy, & warm to hot. Summer into early autumn monsoons can visit sometimes bringing locally heavy rain & thunderstorms. However these are very sporadic & unreliable. Autumn is a short transition period between summer & winter. The weather can be highly variable especially after October. This zone experiences high fire danger almost year round. Heat & cold are extremely variable depending on local exposure & elevation. Strong winds can blow any time of the year & ultra violet light is intense due to the thin atmosphere at high altitude.

Cold Air Basin Microclimates

Cold air moves like water over the landscape. Areas where cold air sinks & collects are called “cold air basins”. At slightly elevated topography cold air drains down & pools into lower elevation areas. The areas where the air drains are in “banana belts” where temperatures are warmer compared to the surrounding lower terrain (which is accepting the pooling cold air). Dry lake beds, areas between hills, & large valleys also collect & trap cold air. These cold air basins can be very small or large in size; they can be an entire valley to a single ditch. These cold air traps can be anywhere, so pay attention to where & when frost or frost damage occurs. Remember cold air flows like water to low places, & can be dammed by impermeable barriers, like walls or embankments. The phenomenon that creates cold air basins usually occurs on clear, cold, still, winter nights. The presence of wind mixes the atmosphere & prevents the air from pooling & “staying put”. This phenomenon does not occur during the daylight. Cold microclimates of desert valley floor include areas like the Owens & Mojave River valleys, Antelope, Lucerne Valleys are also included.

MIDDLE ELEVATION ZONE

Elevation: 2000 to 4000 feet

Precipitation: 3 to 9 inches per year

Average Temperature Range (in degrees F)

Summer: High 90 to 105 / Low 55 to 75

Autumn: High 70 to 95 / Low 40 to 60

Winter: High 50 to 75 / Low 20 to 40

Spring: High 60 to 95 / Low 35 to 60

Maximum Sumer Temps: 105 to 110

Minimum Winter Temps: 15 to 25

Area: This zone encompasses most of the Mojave Desert. It includes the desert hills & lower elevation mountain ranges, & the desert floor (except cold air basins which are in the cold zone). This is a harsh zone that is known for extremes in temperatures, strong winds, & unpredictable weather. Most of the deserts human population lives in this zone. The Victor & Apple Valleys, Lucerne & Johnson Valleys, Landers, Joshua Tree, Yucca Valley, Barstow, Ridgecrest, Dagett, Shoshone, Trona, Ludlow, Mojave, Randsburg, Boron, Antelope Valley, Hesperia, Adelanto in California, Las Vegas, Pahrump, & State Line, in Nevada, Kingman, Yucca, in Arizona, & Saint George, in Utah are all in this climate zone. Some areas are in transition zones to the lower, warmer desert zones. The Morongo Valley & 29 Palms areas are good examples of cities in this transition zone to the warmer Sonoran Desert areas.

Climate Characteristics: The western & south-western regions are wetter during the winter & dryer during the summer, the eastern & northern regions are the reverse. Spring is a short lived transition period between winter & summer. In spring the winds often blow strong & the weather is highly variable & it can be cold one day hot the next. The weather is generally breezy, dry, warm & sunny. Summer brings, breezy, sunny, hot clear days. Summer days can be very hot with temperatures above 110 degrees F with intense sunlight dry air & constant winds make for a very dry environment. Overnight lows are generally mild & there is often an afternoon breeze. Chance monsoons (Chubascos) arrive bringing with them sporadic & unpredictable thunderstorms. These storms can deluge one area, while leaving an adjacent one dry. Eastern & northern regions receive more of the monsoon while the western regions have the least. Autumn is sunny, dry, & is the least windy season. Autumn is probably the most pleasant time in this part of the desert. Early fall is much like summer & hot days can extend well into October. Winter is the rainy season as pacific storms bring strong westerly winds & sometimes rain (even snow). The winter rains are more reliable than those that come in the summer. This Mediterranean climate influence characterizes most of the Mojave Desert (the Sonoran is wetter in summer dryer in winter). Flash flooding is a threat whenever it rains hard. Plants show the most stress during fall & spring transition periods. Wind, sand, & dust storms are common during winter or summer storms. Wildfire danger is high in shrubby areas or on the deserts edge, but because of alien weed species the usually safe desert floor has become more prone to wildfire.

LOW ELEVATION ZONE

Elevation: below sea level up to 2000 feet

Precipitation: 1 to 5 inches a year

Average Temperature Range (in degrees F)

Summer: High 95 to 110 / Low 65 to 85

Autumn: High 75 to 105 / Low 45 to 70

Winter: High 60 to 85 / Low 35 to 50

Spring: High 75 to 100 / Low 45 to 65

Maximum Sumer Temps: 115+

Minimum Winter Temps: 25 to 38

Area: This zone encompasses all areas of the desert below 2000 feet. Some of these areas are below sea level in elevation. The following areas can be included in this zone: the lower Mojave River Valley, lower Colorado River Valley, Death Valley, the Coachella & Imperial Valleys, Palm Desert, Palm Springs, Indio, Mexicali, Imperial & low elevation areas of Joshua Tree National Park, Stovepipe Wells, Needles, Blythe, Desert Center, Baker, the Sonoran Desert areas of Anza Borrego, Coachella & Imperial Valleys in California, Laughlin in Nevada, Bull Head City, Yuma, & Lake Havasu cities, in AZ.

Climate Characteristics: Heat is common spring through autumn. This zone has two scant rainy seasons, one in the late winter & another in late summer. The late summer monsoons are unreliable & can bring sporadic & unpredictable flooding rains & humid weather. Summers are very hot & the lower you go in elevation the hotter it gets, thus areas below sea level bake in summer temperatures as high as 130 degrees! Night time lows also stay warm in low elevation areas. Warm summer nights often cool down only into the 80’s & 90”s. Autumn weather is often hot to warm & breezy. High temperatures topping 100 degrees are not uncommon. Night time lows during the autumn are often mild (even cool) & comfortable. Winters are generally mild, & only in mid to late winter do the strongest pacific storms visit to bringing slow soakings of light to moderate rain. Westerly winds from the Pacific make winter the cool comfortable season. It can get cold at night & frost is not uncommon in some areas. Other areas especially those on slightly elevated terrain are less likely to record hard frosts. Generally frost occurs on a few nights of the year at low elevation areas. The frequency & severity of frost in this zone is based mostly on proximity to cold air basins. Wintertime brings the most spring like weather to this part of the desert. Spring is a short transition period, & often by May it is hot every day (high temps of 95+). Spring in this part of the desert however brings with it strong winds that can usher in cool weather. Rainfall during the spring is extremely unreliable & variable & often very light. Flash flooding is a concern during summer thunderstorms & in large pacific winter storms. Damaging winds & dust / sand storms can occur anytime of the year.

CLIMATE ZONES (FORMAL)

USDA Climate Zone System

This climate zone system was designed by the USDA & is based on the minimum winter temperature. The zones go from 1 (coldest) to 10 (warmest). These zones are well established using data collected over a long period of time. They can be used to describe the basic climate over a large geographic area. The USDA climate zones are based solely on the average minimum or maximum temperature recorded. The USDA climate zones do not take into account rainfall, wind, humidity, & microclimates. The climate of the Mojave Desert can best be described using USDA zones 7 through 9. The colder areas of the Mojave Desert are in USDA zone 7 (minimum temperatures of 10 to 0 degrees F). Most of the Mojave Desert is in USDA zone 8 (10 to 20 degrees f). Only a few mild low elevation areas of the Mojave Desert are in USDA zone 9 (20 to 30 degrees F). However much of the Sonoran Desert in our area is in USDA zone 9 even 10.

Sunset Climate Zones

Sunset Magazine has developed a climate zone system over the last three decades. This climate system provides a more realistic picture about a local climate than the standard USDA climate zones. Sunset zones factor in all climatic conditions. The Sunset climate zones factor in local weather patterns, microclimates, humidity, wind, heat, & cold. The zones are organized from coldest to warmest zone 1 being the coldest & zone 24 being the warmest. The Mojave Desert is best describes by Sunset climate zone 11. Some areas of the Mojave are in the neighboring zones of 10 & 13. In general the Sonoran Desert lies in the warmer zone of 13 (sunset zone 12 exists only in Arizona & New Mexico).

Understanding How Plants Deal With Drought

Plants have evolved many strategies to grow in harsh arid climates. There are two main strategies employed by plants to cope with drought.

Drought Avoidance

Some plants simply avoid drought by growing only when there is moisture & then die or go dormant during drought. Many annuals live a short life (less than one growing season/year) existing as seed in the soil until rains come. Sometimes seeds can lie for many decades before sprouting. Some plants go dormant and stop growing during drought. These plants lose their foliage in dry weather; some even sacrifice branch limbs to conserve water. Specialized root structures store water & nutrients during dry periods (bulbs).

Drought Resistance

In this strategy plants live with drought. They resist drought by employing fascinating anatomical & physiological methods of moisture conservation. Special cells store water in the tissues of the leaf or stem (an example is succulents). Plants have developed protective coverings of hairs, & scales in order to insulate them against drying wind & sunlight. Some plants go deciduous in drought, continuing to grow & photosynthesize through their stems. “Carrot like” tap roots can reach into groundwater, while shallow “Net Like” roots absorb any significant rainfall. Some plants have decreased their surface area & lost their leaves permanently to reduce water loss (Example cacti).

Proper Irrigation Techniques

In arid climates irrigation is extremely important. Several techniques have been developed to irrigate landscapes more efficiently. Water only in the morning or in the evening, this decreases evaporation. The soil can only absorb so much water so make sure that water from sprinklers does not flow off the surface. The deeper the water penetrates the earth the longer you can go between irrigations.

Water Efficient Landscaping

Flooding or slow deep irrigations work the best, bubblers & micro sprays work best. Use mulches to keep the soil cool & moist. Do rely on a timer to water your plants, rely on the weather & how the plants look.

Pay close attention to the texture & drainage patterns of your soil: Dense clay soil drains poorly & can hold onto water. In these soils water less often but for a longer period of time. Sandy well drained soils require more frequent irrigations but for a shorter period of time.

Plant Selection

In order to be a successful landscaper & gardener, one must choose plants that comes from a similar climate as ours. Plants that succeed in our area are tolerant of heat, wind, & cold.

PLANTS & THE LANDSCAPE

ELEVATION & ITS AFFECT ON VEGETATION

The atmosphere is like a blanket; at low elevations the insulating blanket of air is thick, while at high elevations this blanket is much thinner. This means that the higher up we move in elevation the colder it gets. In addition high elevation areas tend to be wetter & more exposed to winds than low elevation areas. In Southern California the cooler moister climate of the mountains houses green forests. The presence of trees & moisture means that there has more organic material in it (generally). Above 10,000 feet it is generally too cold for trees to survive.

LATITUDE

The earth is a sphere at its middle (the equator) receives more sunlight & radiation that at its top & bottom (the poles). The climates of the northern hemisphere are mirrored nearly identically in the southern hemisphere. As you move towards the poles the climate becomes colder & the variation between seasons becomes greater. The closer you move to the equator the warmer & more humid it gets. Seasonal variation becomes minimal.

SOIL AFFECTS ON PLANTS

Soils have a great affect on what type of plants grow on them. Some soils are hostile to plant growth or are poor in nutrients. Some plants exploit these niches. They evolve certain mechanisms to cope with the difficulties. The successful plants are rewarded with having little competition for resources’. What is soil? Soil is both the mineral, organic, gas, liquid, & organisms present in a layer on the surface of the earth. Many organisms in the soil make complex relationships with plants. The texture, drainage, PH, & fertility of the soil are the most important factors.

EXPOSURE

How the lay of the land reacts to the atmosphere is exposure. Ridges, hills, & other elevated topography are exposed to the wind & are often cooler in the daytime. The lee sides of these hill & deep valleys / canyons are often warmer & less windy. Some slope angles increase or decrease heat & drought.

PROXIMITY TO WATER

Water has much to do with moderating the climate. Large bodies of water keep areas adjacent to them close to the temperature of the water. The water bodies also provide moisture, wind, & moderate temperatures.