Introduction to Water in California
By David Carle
UNIVERSITY OF CALIFORNIA PRESS Copyright © 2016 The Regents of the University of California
All rights reserved.
Tapping into a Planetary Cycle
See how every raindrop and snowflake, every skyborne molecule of H2O that falls ... is also a child of Ocean and Sun. ... See how those streams and rivers, as Aldo Leopold pointed out, are "round," running past our feet and out to sea, then rising up in great tapestries of gravity-defying vapor to blow and flow back over us in oceans of cloud, fall once more upon the slopes as rain and snow, then congeal and start seaward, forming the perpetual prayer wheels we call watersheds.
— David Duncan, My Story as Told by Water
Especially as I drink the last of my water, I believe that we are subjects of the planet's hydrologic process, too proud to write ourselves into textbooks along with clouds, rivers, and morning dew.
— Craig Childs, The Secret Knowledge of Water
A GREAT WATER WHEEL
A partnership between land and a planetary water cycle produces the California climate and shapes the natural landscape of the state. California's weather is generated primarily by westerly winds off the Pacific Ocean. In the winter, low pressure in the northern Pacific sends cold, wet storms to the state. California receives 75 percent of its annual precipitation between November and March, the majority from December through February. The dry weather of summer is associated with a high-pressure "dome" over the Pacific. Such "Mediterranean" climates, with wet winters and summer droughts, occur on the west coasts of continents in the middle latitudes due to global patterns of atmospheric pressure circulating over the oceans.
California's rainfall is heaviest in the north and decreases toward the south (map 1). Eureka, surrounded by redwood rain forests, usually receives more than 50 inches of rain each winter. That North Coast town has as much claim to a "California climate" as Los Angeles does, with only 15 inches on average. It does rain in Southern California, contrary to the myth popularized by real estate promoters and Hollywood, and Los Angeles does experience seasons. Winter rains activate the southern California growing season, as dormant plants awake and seeds of annual plants germinate. Summer brings a seasonal drought, and the autumn transition includes hot, dry Santa Ana winds and wildfires. Mountain communities such as Lake Tahoe and Mammoth Lakes experience yet another version of California weather, with six months of winter snow and the brief summer growing season characteristic of alpine landscapes (fig. 1).
California's diverse landscape is responsible for this wide range of precipitation patterns. The state's coastline stretches 800 miles from Oregon to Mexico. A map of California, superimposed over the east coast of the United States, would extend from southern Maine all the way to South Carolina, crossing more than nine degrees of latitude. But California has more diverse weather and climate than the East, because its 100 million acres contain the tallest mountain ranges in the 48 contiguous states and desert basins that lie hundreds of feet below sea level (map 2).
Rainfall and snowfall result when humid air masses blow in from the ocean and interact with the state's mountain ranges. Moist air, moved inland by the prevailing westerlies, pushes up against California's mountain backbones, which wring vapor out of air as it rises, cools, and condenses (fig. 2). Precipitation generally increases two to four inches for each 300-foot rise. Seasonal snowfall totals about two feet at the 3,000-foot elevation in the Sierra Nevada foothills, but increases to 34 feet on Donner Summit, the famous 7,000-foot pass where the Donner party spent a tragic winter. The Sierra Nevada occupies one-fifth of the land area of California and has a major influence on the climate, weather, and water supply of much of the state. Its crest extends 430 miles; 8,000-foot summits in the north rise to over 14,000 feet in the south, intercepting the westerly jet stream at higher and higher elevations. Most of the precipitation in the Sierra Nevada falls as winter snow (fig. 3). In Plumas County, north of Lake Tahoe, an average of 90 inches of precipitation falls at 5,000 feet. The same elevation in the southern Sierra receives as little as 30 inches.
As air descends the east side of California's mountain ranges, the process is reversed. Air becomes warmer and holds more of its water vapor. Relatively dry "rain shadows" are the result. The Sierra Nevada rain shadow creates the Great Basin desert. The Coast Ranges produce a rain-shadow effect for the Central Valley too, although a major gap at San Francisco Bay lets more moisture directly strike the northern Sierra Nevada. The Mojave and Colorado Deserts lie in the rain shadow of the southern Sierra Nevada but are primarily influenced by the Transverse and Peninsular Ranges. The Mojave Desert town of Barstow averages only four inches of rain per year; Imperial, farther south in the Colorado Desert, is even drier (fig. 4).
A broad cross section through the state, beginning near San Luis Obispo and extending roughly northeastward, intersecting the mountain ranges at right angles, would pass through the Central Valley near Visalia, cross Sequoia National Park, and take in the Owens Valley town of Independence. San Luis Obispo, at the base of low mountains in the Coast Ranges, averages 22 inches of rain; Coalinga, in the Coast Ranges' rain shadow and down on the floor of the Central Valley, receives only seven inches. Farther east, just below the Sierra Nevada foothills, Visalia picks up 11 inches. Giant Forest, in Sequoia National Park, is at 7,000 feet; snow and rain there total 46 inches of precipitation (fig. 5). Independence is in a desert created by the Sierra's rain shadow and averages only five inches of rain. East of the White Mountains, in Death Valley, 178 feet below sea level, annual precipitation is a mere two inches at Greenland Ranch (fig. 6).
California receives almost 200 million acre-feet (MAF) of precipitation in an average year. One acre-foot (AF) equals 325,851 gallons, which would cover a football field one foot deep. Planners commonly figure that an AF serves the annual domestic needs of one to two families, or five to eight people, depending on how wisely it is used and conserved. Water that falls on the state may evaporate back into the atmosphere, be used by plants that then return vapor to the air, or soak deep into groundwater basins. What remains is about 71 MAF of "runoff" water, which moves across the landscape and is the water most accessible to people. Streams draining the sodden North Coast contain about 40 percent of this runoff. The Sacramento River basin generates another 31 percent, mostly originating with the Sierra Nevada snowpack. Snowmelt from the southern Sierra drains into the San Joaquin and Tulare Valleys, producing much of the balance (map 3). The Colorado River receives almost no runoff originating inside California, but because the river serves as the state's southeastern border, California receives 4.4 MAF from it. This apportionment, along with Klamath River water out of Oregon, allows water planners to figure on a statewide supply of 78 MAF of annual runoff.
The Sierra Nevada snowpack has historically peaked by April 1 and then begun melting. By midsummer it is gone, except for a few small glaciers and snowfields on north-facing exposures that are shaded from direct sunlight. The delayed release of snowpack water overlaps only partly with the optimum growing season for plants in California. Moisture is most available in the winter, when temperatures are low, and is scarce during the long, warm days that optimize growth. Urban and agricultural water demands are out of sync with the natural runoff pattern, peaking during summer and at their low point during winter. California's natural vegetation evolved adaptations to the local patterns. Many annual plants flower quickly in spring and produce seeds that sleep through the long drought of summer and early autumn. Winter rains break that dormancy. Some perennial shrubs and trees rely on deep root systems to tap water even during the long seasonal droughts. Others go dormant, simply shutting down their metabolisms. Riparian vegetation found along riverbanks and in wetlands benefits from year-round water availability. The New England pattern of four seasons — lush, green springs; hot, wet summers that encourage plant growth; autumn color before leaves are dropped; and freezing winter weather — is found in California only in mountain and foothill river canyons. There plants can keep their roots wet and local hydrologic conditions mimic the New England pattern (fig. 7).
Water moving within California is part of a greater planetary water cycle that includes many circular movements, wheels within wheels (fig. 8). Water is continuously shifting among three "reservoirs": the ocean, the atmosphere, and the land. These are connected by precipitation, evaporation, and plant absorption and transpiration (evaporation through leaf pores). Water is perpetually changing form and traveling the globe. It has been said that we drink the same water the dinosaurs drank. That is not accurate for specific water molecules. During photosynthesis, for example, these molecules split into oxygen and hydrogen atoms. Yet it is true that no water is lost in the overall planetary balance; water returns. The respiration of plants and animals recycles it, reversing the photosynthesis equation by consuming oxygen while breaking complex molecules into water and carbon dioxide. Fire, an important decomposition agent in the natural California landscape, produces the same chemical results. And when organisms die and decompose, water is reconstituted.
This planetary recycling is powered by the sun, which evaporates water from the ocean and the land. In photosynthesis, the sun's energy is also what splits the bonds holding water molecules together. Of the water vapor returned to the atmosphere, 16 percent comes from transpiration by land plants (fig. 9); most of the rest comes from the ocean. At any given moment, only a thousandth of one percent (0.00001) of the planet's total water is in the air. Yet that small percentage produces thick coastal fogs, dramatic thunderheads, and drenching downpours. In a journal entry written during a January storm, John Muir marveled "that so much rain can be stored in the sky" ( 1979, 335). The recycling that replenishes atmospheric vapor is so constant and voluminous that this water is completely replaced every eight days and the equivalent of all the oceans' water passes through the atmosphere every 3,100 years.
Two-thirds of the Earth's surface is covered by liquid water. Philip Ball wrote, in Life's Matrix: A Biography of Water (2001, 22), "We call our home Earth – but Water would be more apt." Over 97 percent is salt water, though, and over two-thirds of the fresh- water is locked up in ice caps and glaciers. Less than one percent of the total is available freshwater, with most of that below ground, in aquifers that are never fully accessible. On this watery planet, just 0.016 percent (0.00016) of the precious fluid is "active" freshwater, moving through lakes, rivers, the atmosphere, and living creatures (fig. 10).
The cogs in the water-recycling wheel revolve at different speeds, like different-sized gears meshing inside an enormously complex clock. Vapor evaporated from the surface of the sea may circulate for only a few hours or for days. Deep ocean water may take thousands of years to complete a circuit of evaporation, condensation, and return. Some of the water in the polar ice caps may remain solid for millions of years. The ice in some small Sierra Nevada glaciers has been there for nearly a thousand years. Under certain conditions, groundwater can be trapped in deep, confined aquifers, held back from the water cycle for thousands of years. At its own speed, however, groundwater does participate in the cycle. It feeds springs, rivers, or lakes, and it is replenished when surface water percolates into the ground.
Water may travel for weeks through California's river arteries before finally returning to the sea or terminating its journey in inland waters such as Mono Lake. Almost anywhere along these routes it may be shunted aside, pulled in by the roots of a plant, or drunk by an animal.
Water is essential for life on Earth and is the critical habitat factor that shapes California's ecosystems. As the leaf and root designs of plants adapt to climate, elevation, soil, and topography, both the gathering and the conservation of water are of supreme importance. Bands of different flowers lining a vernal pool sort themselves out by their particular relationships with water. The spiny leaves of a Joshua tree (Yucca brevifolia), like the extremely efficient kidneys of a kangaroo rat, are water-conservation adaptations to life in the desert (fig. 11). Indeed, everywhere in the state — in the wetland marshes rimming San Francisco Bay, the grassy prairies of the Central Valley, the north coast rain forests, the chaparral shrublands of southern California, the foothill oak woodlands, and the pine forests of the Sierra Nevada — all forms of life accommodate to the local availability of water. Photosynthesis requires water, often in enormous amounts. Plants combine water with carbon dioxide to manufacture food for themselves and the herbivores that feed on them; in the process, they replenish the atmosphere with oxygen gas.
Various mechanisms and behaviors foster "best management practices" for water conservation by living things. At the boundaries between multicellular bodies and the rest of the world, barriers of skin, bark, scales, or mucous membranes regulate water passage in and out. Every living cell has a membrane that encloses and regulates its internal concoction of water and essential chemicals. Multicellular organisms bathe their cells in watery environments. Water management is critical to homeostasis, the maintenance of the internal conditions necessary for life.
We are bodies of water. Humans can live without food for weeks, but die within days when deprived of water. Our bodies are 65 percent water (our brains more than 95 percent); a 150-pound human body contains over 12 gallons of water. We need to replenish about two and a half quarts a day, one-third from drinking and the rest in foods, as we lose water in breath, sweat, and urine. Water is the primary medium for biochemical reactions and a participant in many of the essential processes of life. It helps break down our food, then carries the digestion products to our cells. It regulates temperature and transports dissolved oxygen and carbon dioxide through our circulatory systems. Proteins that rely partly on their shapes to fulfill their jobs as enzymes are folded into those shapes by bonds with water in the fluid of our cells. As cellular metabolism generates wastes, water dissolves them and moves them across filtration membranes in our kidneys, returning them (and the water itself) to the environment.
Water is so essential to us that it is amazing we ever take it for granted. If it is our most precious resource, that is not simply because the supply sometimes grows scarce. H2O is the vital essence of life on Earth, an almost magical molecule. A full appreciation of our relationship with California water begins at the molecular level.
THE VITAL MOLECULE
Water is so familiar that we seldom give any thought to what sets this particular molecule apart from other substances commonly found in our lives. Unusual characteristics are behind water's critical importance. "Water is life's true and unique medium," Philip Ball has written. "That the only solvent with the refinement needed for nature's most intimate machinations happens to be the one that covers two-thirds of our planet is surely something to take away and marvel at" (2001, 268).
Most solids, liquids, or gases that we encounter naturally are found in just one phase. Minerals, such as silica or calcium carbonate, that form rocks and soils remain solid (unless heated to extremes by volcanic action or movement of the plates that form the Earth's crust). Other elements and compounds, too, stay in a single phase under normal circumstances. "Silicon vapor" is not part of our daily experience or vocabulary. Neither is "liquid wood" or, for that matter, "solid air." Decomposition or digestion breaks molecules apart to build something new, but this is not simply a matter of phase changes. The water molecule, however, is widely abundant on this planet in all three phases: as solid ice, liquid water, and gaseous water vapor (fig. 12). When most other molecules are transformed, those changes regularly involve water because it is so nearly ubiquitous, dissolves most anything, and is good at carrying other materials along with it.
The explanation for water's unusual phase character also helps explain why water contains "an invisible flame ... that creates not heat but life," as described by David Duncan in My Story as Told by Water (2001, 190). Water is a "community molecule." That is, water molecules constantly form, break, and re-form bonds with one another. Those bonds produce a cohesive tendency that is behind most of water's special attributes. Working together, H2O molecules pick up the colors of the sky, create the pleasing sounds of water and gravity working together, and shape our most beautiful landscapes. (Continues...)
Excerpted from Introduction to Water in California by David Carle. Copyright © 2016 The Regents of the University of California. Excerpted by permission of UNIVERSITY OF CALIFORNIA PRESS.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.