Sonoran summer showers catalyzes cross-border research

Those who have gone into space have come back with a changed perspective and reverence for the planet Earth. For those of us in the Southwest, a trip into space isn’t necessary – we need only look out our window to become acutely aware of the fragility of the Earth and the delicate balance that we must maintain to survive.

ASU hydrologist Enrique Vivoni played a leading role in preparing a special issue of the Journal of Arid Environments that documents recent progress on understanding the ecohydrology of the southwest United States and northern Mexico. Ecohydrology is an emerging interdisciplinary science that attempts to understand and predict the interactions between vegetation, landscapes and water. 

Covering almost 40 percent of the Earth’s landmass, and home to nearly one-sixth of the world’s population, arid and semiarid regions warrant a careful examination of their ecohydrological processes and feedbacks. As in other similarly parched regions, southwestern North America is considered to be vulnerable to the effects of climate change, particularly rising temperatures and changes in precipitation. These landscapes are also greatly influenced by summertime precipitation generated by the North American Monsoon. Variations in seasonal precipitation in this region lead to a set of cascading effects on the ecohydrological processes occurring on the land surface.

“While the summer monsoon is widely recognized in studies of North American deserts, there have been few coordinated bi-national efforts to quantify the interacting processes that characterize its ecohydrology,” said Vivoni, one of the guest editors of the special issue and an associate professor with a joint appointment in ASU’s School of Earth and Space Exploration in the College of Liberal Arts and Sciences, and the School of Sustainable Engineering and the Built Environment in the Ira A. Fulton Schools of Engineering. 

Given the interdisciplinary nature of ecohydrology, it is only appropriate that the journal’s special issue be the result of collaborations among several U.S. and Mexico institutions working to understand the region from multiple perspectives, ranging from grassland ecology to micrometeorology. The idea of developing a special issue focused on this the U.S.-Mexico border region arose from a successful session that Vivoni helped organize at the American Geophysical Union Spring Meeting in 2007. 

“It was clear by then that the scientific community had begun to coalesce around studies of the hydrology, meteorology and ecology of the North American Monsoon,” Vivoni said. “The Journal of Arid Environments appealed to us because of its broad international readership, specifically in countries within the developing world that have arid or semiarid climates, as well as its wide intellectual reach, spanning from studies of desert botany to investigations of climate change in deserts.” 

Vivoni and his colleagues solicited studies from U.S. and Mexican research groups that conduct activities in the region. Twelve contributions were eventually published, representing a large number of institutions in the two countries and an interesting set of collaborations between American and Mexican partners. 

With its major interests lying in the overlap between hydrology, meteorology, ecology and geomorphology, Vivoni’s surface hydrology research group at ASU studies the integrated watershed response through numerical simulations, remote sensing and field observations. His group has been examining the ecohydrologic response to the summer monsoon for several years. 

“We have research activities in several areas in New Mexico, Arizona and Sonora, Mexico. Most of our current work is funded by several grants from the U.S. Army Research Office, NASA, the National Oceanic and Atmospheric Administration and the National Science Foundation,” Vivoni said. “In each of these projects, we are focusing our efforts on understanding different aspects of the seasonality of land surface conditions – soil moisture, vegetation, runoff generation and flooding – during the summer monsoon season.” 

This summer, his research group, including three graduate students and one undergraduate, is deploying a new hydrologic sensor network at the Jornada Experimental Range in Las Cruces, N.M. The site is a Chihuahuan desert shrubland and is representative of broad areas that are used in the southwest U.S. as rangelands for cattle grazing. Installed in a small watershed, the sensor network is designed to obtain measurements of the watershed energy and water fluxes, including precipitation, evaporation and channel runoff. Vivoni and the students hope to derive a unique data set that can help test a numerical model of the site and to explore the seasonality in the water, energy and carbon fluxes in this ecosystem. 

Vivoni will visit the site at the end of May to witness an unmanned aerial vehicle (UAV) flight conducted by collaborators at Jornada. Later in the summer, Sri Saripalli, a roboticist and assistant professor in the School of Earth and Space Exploration, will participate in the study by using his own UAV sensors at the watershed site to derive a high-resolution topographic map. The goal is to combine the UAV measurements with the hydrologic sensor network and numerical modeling to investigate and predict the ecohydrologic conditions at the site, as a representative of broad regions in the southwest U.S. 

“What we learned through the special issue of the Journal of Arid Environments is now informing a set of new studies within the North American deserts. Our work at the Jornada Experimental Range is one example of the efforts we will conduct over the next few years. I believe this issue will impact the broader community as it brings together important studies conducted within the common framework of the land surface ecohydrology of the North American Monsoon,” said Vivoni, who is now an associate editor of the journal. “We now need to work on the next generation of studies that seek to understand the human impact, via climate and land-use change, on the ecohydrology of the southwest U.S and northern Mexico in an effort to predict the future in these fragile landscapes.”

To access the special issue, please visit: http://www.sciencedirect.com/science/journal/01401963