Satellite imagery and models to help secure water resources in the arid Southwest

February 17, 2016

In the arid Southwest, roughly 90 percent of the region’s rainfall evaporates, leaving relatively little water to fill streams and reservoirs or soak into the ground. Predicting this evaporation, and its responses to changes in land use, is essential to managing precious water resources. 

Arizona State University scientists Ted Bohn and Enrique Vivoni, of the School of Earth and Space Exploration, discuss a new technique in the journal Water Resources Research, which uses a combination of satellite imagery, field observations and models to estimate evapotranspiration - evaporation from soils and from plant transpiration. Evapotranspiration is an important component of the hydrological cycle and a major contributor to downwind rainfall. Average annula evapotranspiration from the North American Monsoon Region Average annual evapotranspiration from the North American Monsoon region, 2000-2012, as simulated by the Variable Infiltration Capacity model, release 4.2. Download Full Image

Bohn and Vivoni used a well-established model to study evapotranspiration in southwestern U.S. and northwestern Mexico, but modified it to account for soil evaporation, irrigated agriculture, and the seasonal variability of the land surface. An important difference from previous studies was the inclusion of irrigated agriculture in the model. 

The study derived seasonal changes in irrigated areas and vegetation greenness from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS), a key instrument aboard the Terra and Aqua satellites, which view the entire Earth’s surface four times per day.

“The results of our study hold great promise for satellite monitoring of irrigation water usage on a global scale,” says Bohn, “particularly in nations that lack good records or policies of data transparency.”

The scientists then compared field observations with simulated patterns of evapotranspiration. In doing so, they discovered that different ecosystems vary dramatically in the timing of evapotranspiration in response to summer monsoon rains.

Desert shrub lands, for example, produce their peak evapotranspiration shortly after monsoon rains begin, while mountain forests are slower to peak and continue evapo-transpiring well into the autumn.

In contrast, evapotranspiration from irrigated agriculture has little relationship with rainfall, and exhibits two peaks per year, during the winter and summer cropping seasons. These observed differences in peaks show that expansion or reduction of agriculture can dramatically change the timing and amount of local evapotranspiration, with potential effects on rainfall.

“It turns out,” says Bohn, “that irrigated agriculture accounts for almost ten percent of the region’s annual evapotranspiration, which is a large amount for previous studies to have ignored.”

A major benefit of the modified model used for this study is a better understanding of our water resources, and how they respond to changes in land use.

“It will allow not only for more accurate climate and weather forecasts, but also for government agencies to plan better for anticipated changes in climate,” says Bohn.

Karin Valentine

Media Relations & Marketing manager, School of Earth and Space Exploration


A solar-powered San Diego spring break

February 17, 2016

This March 11 Arizona State University engineering students will be headed to San Diego for spring break. While that doesn’t sound unusual this time of year, they’re not only going for fun.

These students, earning a Professional Science Master’s (PSM) in Solar Energy Engineering and Commercialization (SEEC) from the Ira A. Fulton Schools of Engineering, are participating in Solar Spring Break, a program from GRID Alternatives where college students install solar panels in underserved communities. Solar Spring Break 2015 Professional Science Master's Solar Energy Engineering and Commercialization students install solar panels as part of the Solar Spring Break program in 2015. Photo courtesy of GRID Alternatives. Download Full Image

Solar Spring Break gives low-income families access to renewable energy and its cost-saving benefits when they otherwise wouldn’t be able to afford or access it. Participating students get a first-hand experience in the fast-growing solar energy industry. The SEEC program is participating for the second year.

“It has become a legacy endeavor in our program,” said SEEC graduate student Tomasz Jasinski. “Everyone who went to the program says it’s so rewarding.”

Beginning on March 7 — spring break runs from March 6-13 — they’ll spend two days in training learning how to install a solar system.

“It’s going to be both exciting and educational,” said Aakash Bhansali, leader of the SEEC Solar Spring Break group. “We’ll be interacting with engineers, learning how things are done and getting the training to become a certified installer, though we won’t receive official certification. We like having hands-on experience and not just learning from books.”

The following two days they’ll install the system on one family’s house in the San Pasqual Indian Reservation outside of San Diego with equipment provided by GRID Alternatives.

SEEC graduate student Nicholas Fortenberry, who attended last year’s program in Atascadero, California, found the whole process of installing a solar system to be informative.

“I didn’t fully understand optimizing a solar module for maximizing power generation until I went on the trip,” Fortenberry said. “We learned about the design process from GRID Alternatives. We did site surveys. We did promotion for the organization. We installed and took part in the racking system, clamping systems, electrical wiring, the modules, inverters — everything.”

At the end of the week they’ll check the system, clean up and unveil it to the family.

The big draw of Solar Spring Break, which has spread by word of mouth to the 2016 students, is the rewarding experience of seeing the family’s electric meter roll back after the solar system is turned on.

“My favorite part was when we finally activated the system after everything was installed and wired,” Fortenberry said. “After turning it on, the electrical meter began to run backward as excess electricity from the solar system poured back into the grid, allowing the family we worked for to not only offset their own power use, but to put excess solar generated power into the grid for other people to use. Seeing the meter go back meant everything was working and our family was saving money and offsetting carbon emissions.”

Along with experiencing the small-scale, single-house solar system installation, PSM SEEC program manager Karen Dada set up a trip to check out a solar farm on their way to San Diego. Last year’s group went to the Topaz Solar Farm, one of the world’s largest solar farms, in the Carissa Plains in Central California and got to talk with their engineers.

The overall experience will be very educational for the PSM SEEC students, who study solar energy engineering, energy policy and project financing — an “MBA meets solar engineering” program as Jasinski describes it — in a program that can be completed in 12 months. And this isn’t the first time the students have traveled together. The PSM SEEC program includes a week-long energy policy seminar in Washington, D.C., to network with solar industry professionals.

It’s still important to unwind and recharge for the rest of the semester, so it won’t be all work and no play for the SEEC students. They’ll take a couple extra days to soak up at the beach, check out the sights in San Diego and let loose before they hit the books again on March 14.

Interested in applying for the Professional Science Master’s Solar Energy Engineering and Commercialization program? Applications are now being accepted for fall 2016 enrollment. Visit or contact Karen Dada ( for more information.

Monique Clement

Communications specialist, Ira A. Fulton Schools of Engineering