A Major Grant to Model the Monsoon
Sweeping across the desert Southwest in the late summer months, the Arizona monsoon not only brings rains and relief from the scorching heat, it also makes the Sonoran Desert stand out from other deserts across the world by supporting an unparalleled diversity of fauna and flora.
Every year in late April or May, as the sun travels north in its seasonal progression, large, high-elevation land surfaces in Mexico begin to warm up. As the air over the land warms and rises, it draws moisture from the Sea of Cortez, also known as the Gulf of California, a short 150 miles away.
"Moisture comes in and as the land continues to heat up moving northward, that moist air also moves northward," explains Russell Monson, Ph.D., Louise Foucar Marshall Professor and principal investigator for the grant. UA co-investigators include Chris Castro, Francina Dominguez, Xubin Zeng, Guo Yue Niu, Tom Swetnam, Steve Leavitt, Connie Woodhouse and Julio Betancourt.
As it advances, daily warming at the land surface gives the air upward lift, which creates the late-afternoon thunderstorms in May and June in Northern Mexico. By July the storms begin to reach Tucson. And those powerful storms bring warm winds, torrential downpours and spectacular lightening displays.
To better understand the complex processes by which this unique phenomenon influences ecosystems and natural cycles, the National Science Foundation (NSF) has awarded almost $3 million to fund the team’s research aimed at unraveling the interactions between weather, soil and plants linked to the monsoon phenomenon.
The grant is one of only two research proposals considered "outstanding" across all categories evaluated by the NSF from a pool of 50 competing applications.
"We are constructing a highly coupled computer modeling system between summer weather and ecology that has never been constructed before for this part of the world," said Monson, who recently joined the UA's School of Natural Resources and the Environment and the Laboratory of Tree-Ring Research.
"Traditionally, ecologists have tended to focus on individual ecosystems, small study sites and limited populations of organisms," he added. "What we're doing under this NSF grant is broad, regional-scale ecology. It's a new way of practicing and thinking about ecology."
Through their studies, the team will investigate the timing of monsoons, how they affect invasive species like cheat grass and buffelgrass, and how those species affect weather through altering reflected solar energy from the ground and rates of evaporation.
In a second line of research, they will do tree-ring analyses to discern historical patterns of the monsoon system and use historical data to validate the predictions of their models.
"What we want to do now is bring the ecological perspective into play with our strength in weather modeling,” says Monson. “How does the monsoon and its variability influence tree growth, spread of invasive grasses in the western U.S. and the propagation of fire cycles?"
Xubin Zeng, a co-principal investigator and professor in the UA's Department of Atmospheric Sciences and director of the UA's Climate Dynamics and Hydrometeorology Center, adds: "A unique aspect of this grant is the equal focus on atmospheric science and ecology on the ground. This is the first time we integrate invasive plant species with weather and climate modeling. Nobody has done this before."