March 14, 2006
Research conducted by University of New Mexico scientists presents evidence that El Niño-mediated winter storms are more important than previously suspected for controlling moisture availability in the U.S.-Mexico borderlands region.
The research describes evidence of a mid-Holocene wet climate episode not recognized in any other record from southwestern North America. The Holocene is generally recognized as the last 10,000 years of Earth’s history.
“Contrary to the current paradigm for climate in the region, our results establish that Holocene moisture availability is not solely controlled by summer monsoon precipitation,” said former UNM graduate student Peter Castiglia, now a geologist with SWCA Environmental Consultants. “We’re helping to redefine a 50-year-old paradigm of climate conditions in this area over the last 10,000 years.”
“Our main finding is that millennially spaced wet periods have caused currently dry basins in the Chihuahuan Desert to fill with regionally unprecedented amounts of water several times over the last 10,000 years,” he said.
These basins had an area approximately 51 times the surface area of an “almost full” Elephant Butte reservoir in New Mexico and spanned the border between the U.S. and Mexico. During a period that was previously thought to have warmer temperatures than present times, one lake had 1.5 times the surface area of an almost full Elephant Butte reservoir.
The research studied lake-level variations preserved as well-defined beach ridges in the Laguna El Fresnal and Laguna Santa Maria sub-basins in northern Mexico. The millennially spaced episodes of increased precipitation are punctuated by periods wet enough to establish large pluvial lakes (those formed by abundant rainfall) in the now-dry basins in the Chihuahuan Desert. The area encompasses a critical climatic boundary region between the subtropics and the middle latitudes.
“We were surprised the lakes were so young,” said Castiglia. “We didn’t know lakes this large could exist at this time. The strong correlation with other wet and cold events documented in records from outside the monsoon moisture system shows that winter storms played a more important role in controlling regional climate than previously suspected. Understanding the magnitude, frequency, and mode of moisture trends in the borderlands region is a central component for water-management policy and climate change research.”
Using a lake-level record from a closed basin in the modern North American monsoon moisture period, Castiglia and UNM Earth and Planetary Sciences professor Peter Fawcett reconstructed changes in wet and dry periods. A series of lake “high stands” in the U.S. and Mexico borderlands region is synchronous with ice rafting events in the North Atlantic and glacial advances throughout the western U.S., as well as wet and cold intervals recorded in other sediments, tree rings and ice cores.
The few existing records examining climate change from this same region lack sufficient detail and resolution to establish that winter storms are important for driving millennial-scale climate oscillations in this semiarid region of North America, according to the researchers.
The findings dramatically alter the climatic framework used by geologists reconstructing past climate change; archaeologists describing human responses to environmental change; and water managers tasked with balancing environmental, agricultural and urban water needs in drought-stressed southwestern North America.
“Understanding the magnitude, frequency and mode of moisture trends throughout the U.S.-Mexico transboundary region is a central component of the numerous federal programs concerned with climate change research,” said Castiglia.
Federal agencies tasked with developing long-term water-management plans for the borderlands region include the U.S. Bureau of Reclamation, International Boundary and Water Commission and Comisión Nacional del Agua of Mexico. This record will allow policy makers and water managers to identify historic wet intervals and place the present drought conditions in the context of the last 10,000 years, according to the researchers.
“This is the first of what I hope leads to other studies of hydrology of the systems involved,” said Castiglia. “I hope it can be linked to regional archaeological evidence of human migration patterns. The key step is to use these field data to test climate models as a basis for sound policy decisions related to resource-management in the region.”
Source: University of New Mexico.