In the slides on hydrologist Marc Parlange's desk, the crusted surface of the Owens Lake bed looks thin, hard and white. There is no obvious water, vegetation or animal life.
The pictures illustrate the subject of Parlange's professional zeal,
deciphering the relationship between environmental forces and water."Evaporation is really the major cause of water loss in California because most of the state is arid," Parlange says. "This whole Central Valley would be an entirely different place if it weren't for irrigation."
Water leaves the ground, rivers and lakes fairly rapidly, he explains. Evaporation continually withdraws water from open lakes and rivers just as it does from living organisms, and the rate depends on the size of the surface area exposed to wind conditions, temperature changes and the surrounding humidity level.
In the Owens Lake slides, graduate students can be seen positioning a cylindrical instrument called a neutron probe into the thin dry soil. The probe will send tiny neutron particles into the ground that will, in turn, send back a signal to the probe. The stronger the signal, the lower the water content of the soil.
Measurements collected in this alkali wasteland have revealed secrets to Parlange about the moisture content, wind conditions and temperature in the region where soil meets air. The role these environmental characters play in the never-ending cycling of water, especially the return of water to the atmosphere, is the focus of the UC Davis associate professor's work.
In a slightly Gaelic lilt fused with enthusiasm, Parlange says, "There's a hydrologic balance between the land and the air above that can directly affect water conservation efforts. Understanding how much and how fast water is going from one location to another in the state is really key."
Parlange's interest in water was fostered in the arid climate of Australia where he studied applied mathematics as an undergraduate. His French father and Irish mother chose to live on one of the driest continents of the world for several years before returning to the United States.
He completed a master's degree in agricultural engineering and a doctoral degree in civil and environmental engineering at Cornell University. Then he came to UC Davis, acting on the advice of his adviser, UC Davis alumnus Wilfred Brutsaert. Some may remember Brutsaert for his accomplishments at UC Davis as a track runner but more will remember him as last year's engineering alumnus of the year, awarded for his academic contributions to hydrologic science.
"Brutsaert was always pumped about UC Davis and really bolstered my idea to stay in academia," Parlange says. He accepted a teaching position in the land, air and water resources department here and moved from humid Ithica, N.Y., to the arid climate and rich soils of Davis. Parlange combined his expertise in mathematics and engineering with his interest in agriculture and the environment to model how the atmosphere directly above the Earth's surface interacts to bring about evaporation. In the six years he has been a faculty member, Parlange has proved to be a prolific publisher of research findings. He also teaches courses in fluid mechanics and analytic hydrology, as well as a cross-discipline course that combines micrometeorology with evaporation in hydrology. His research is focused regionally with financial support from NASA, the U.S. Department of Agriculture Hydrology Lab and Los Alamos National Labs in New Mexico. He and his colleagues share an ultimate goal, which is to devise better water management tools that one day will involve tracking evaporation rates globally with instruments mounted on satellites.
Owens Valley is one of his field study sites and Campbell tract in west campus just north of the environmental and agricultural services facilities, another. Parlange and his students explore the role of wind, temperature and humidity and their relationship to water that prompts its return to the air as vapor. Their expertise is data collection in dry regions of high turbulence. Turbulence is common close to the ground where wind speeds and air pressures fluctuate randomly. This jostles the instrument's sensing mechanism, making readings erratic.
Modeling these chaotic conditions is nearly impossible but ultimately necessary, Parlange says. This is because the two most important areas to measure water content are the the lowest part of the atmosphere (called the atmospheric boundary layer) and under the soil closest to the surface (called the vadose zone). These the two regions, one atmospheric and one terrestrial, are interconnected; one will influence the water content of the other. The lack of uniformity throughout these regions aside, working beneath the soil means "working in the dark which presents challenges that will be around for decades to come," Parlange adds.
"An accurate picture of evaporation depends on really precise readings of water content close to the Earth's surface," says Parlange who is using remote sensing equipment on loan from NASA to capture and quantify the constant mixing and blending of water vapor as it rises off the planet. From a position above the ground, the instrument can collect the necessary data. Parlange and his graduate students also have created calibration strategies to improve the accuracy of their readings.
The researchers use the concept of a "budget" to map water as it cycles from precipitation to evaporation and back again. "If you view your salary as precipitation, the taxes taken out of that check are evaporation," Parlange explains.
A portion of the remainder is divided up as savings--the terrestrial equivalent of water collected in reservoirs--or as ground water, and a portion spent on essential items like drinking water and agricultural irrigation. The remainder is the discretionary portion of the water budget used for anything from swimming pools to decorative fountains. Measurements of how much water has returned to the atmosphere at any given time enable Parlange to deduce the remaining volume held in the ground or reservoirs. He says this awareness could furnish more powerful tools that generate drought and flood predictions. These tools could help minimize the use of water for irrigation by helping farmers with the over-irrigation trend, "a really big problem here that is damaging soil and water quality," Parlange says.
"Evaporation, the largest portion after precipitation of the water budget, is the least well understood," he says.
Combining theory development commingled with extensive field experiments, he has created a model that represents the evaporation portion of the water budget in what he believes to be the most accurate picture ever presented. What seems in many ways like endless computation scribbling and discussions of the timeless unsolved puzzles of physics may one day help fulfill California's ever increasing water demands.
