Modeling the Future

Range scientist Jon Hanson notes the effects of four global change scenarios on calf weaning weights. He then compares them with the Range Dependency Index (on the monitor) showing the percentage of a region's income that is linked to range beef production.

Many people use a computer in day-to-day activities, be it to get cash from an automated teller machine or to compose a letter. But scientists and engineers first used--and continue to use--the power of computers to analyze complex problems like potential climate change.

Computer models help researchers get a handle on how environmental changes might affect plants, animals, water supplies, and even human comfort. In the agricultural arena, these models often go by a strange-appearing combinations of letters. Some of these are EPIC, RZWQM, CREAMS, SRM, WEPP, SHAW, NLEAP, and SPUR2.

"Historically, ARS has solved agricultural problems on field, regional, and sometimes even a national scale--but not on a global level, " says ARS soil scientist Ronald F. Follett. "But because we have decades of research on soil, water, crops, natural resources, and other issues that are important to global change, scientists who run global models are looking to ARS for information."

Based in Fort Collins, Colorado, Follett heads up research that focuses on the cycling of carbon and key greenhouse gases between the atmosphere and land.

From the beginning of ARS' involvement in the U.S. Global Change Research Program, scientists recognized the need to develop models of plant and soil processes and to scale them up to make regional predictions. The agency's scientists were well qualified to do this, having developed models that worked at the field level for many years.

Root Zone Water Quality Model (RZWQM).

"ARS researchers nationwide continue to develop the needed models," says Basil Acock, an ARS plant physiologist at Beltsville. "Many are modular so that each component can be plugged in or taken out without affecting the overall function of the larger model. This standardization allows researchers to borrow various components developed by others, and it avoids duplication of effort," he says.

The models will improve estimates of plant growth and yield, greenhouse gas emissions and sinks, and water and energy flows on cropped lands, forests, and rangelands. Others will simulate changes expected because of pests, diseases, and salinity.

The scientists run "what would happen if..." scenarios over 10- to 100-year periods. That should provide clues on how to mitigate global climate change.

"Whatever model we use to predict change, it must be responsive to all environmental factors--temperature, nutrients, water, and more importantly, land management," says Jon D. Hanson, an ARS rangeland scientist at Fort Collins, Colorado. He developed SPUR2 (Simulation of Production and Utilization of Rangelands), one of the agency's most complete models for predicting how climate change would affect U.S. cattle-grazing areas. His research suggests that the country's best grazing lands could gradually shift more to the east and north.

ARS is uniquely equipped to conduct studies in global change because it has acquired long-term hydrology and climate databases, some covering more than 40 years. The hydrology data come from measurements made on large watersheds located near Tucson, Arizona; Tifton, Georgia; Boise, Idaho; Oxford, Mississippi; Coshocton, Ohio; El Reno, Oklahoma; University Park, Pennsylvania; and Temple, Texas. Much of the data is archived at the ARS Water Data Center, part of the Hydrology Laboratory at Beltsville. ARS laboratories in Fort Collins, Coshocton, El Reno, and Temple provide the climate data.

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Climate's Impact on Snowpacks

Global warming predictions indicate that the amount and timing of snowmelt and runoff may change in western basins like ARS' Reynolds Creek Experimental Watershed near Boise, Idaho.

Some of the best water on Earth comes from the melting snowpacks of high-mountain watersheds in the western United States. These rugged basins provide 50 to 80 percent of the West's water for cities, farms, ranches, hydroelectric power plants, and other downstream destinations.

"But even a modest warming or cooling of our climate," says Keith R. Cooley, "could change the timing and amount of snowmelt." He's an ARS hydrologist at Boise, Idaho.

That's why Cooley and colleagues are expanding and fine-tuning computer-based mathematical models that predict how changes in the Earth's climate may quicken--or delay--snowmelt from tomorrow's snowpacks. Equally as important, they are working to improve their estimates of changes in the amount of runoff that snowpacks of the future will provide.

Three such models predicted remarkably similar trends when used to project changes in timing and yield from western snowpacks. The study was the first of its kind to encompass such a diverse assortment of western watersheds, says Albert Rango, an ARS hydrologist at Beltsville.

For the experiment, Rango and Cooley selected seven watersheds scattered throughout four western states and Canada. These basins ranged from sagebrush-clad slopes that receive an annual average of about 20 inches of rain or snow to thick forests of spruce and fir that receive about 50 inches. The researchers programmed the models to predict what might happen to snowfields if the Earth's atmosphere were 5^oF to 9^oF warmer.

Estimating the volume of water contained in snowpack is vital to forecasting how much water will be available for agriculture and other uses.

Global warming, the researchers report, would cause snowmelt and runoff to start--and to peak--earlier in the year. "The greatest volume of runoff could occur not in May or June, our typical snowmelt months," says Cooley, "but instead in March or April. That means western farmers of the next century may have to make new choices when deciding what kinds of crops to plant."

What's more, the snowpack might yield less water. "A warmer climate," explains Cooley, "not only causes the runoff to occur sooner, but may also cause less snow to accumulate at certain elevations.

At the time it was selected for the seven-basin study, the Snowmelt Runoff Model, or SRM, that Rango developed relied primarily on temperature estimates. Today's SRM takes into account two other key factors--radiation and cloud cover. Rango says a cooperative research and development agreement between ARS, the industry-sponsored Electric Power Research Institute, and the U.S. Geological Survey funded part of the work that led to the newer, more savvy model.

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SALSA--the SemiArid Land Surface Atmosphere Program

Arid regions, which get less than 10 inches of precipitation annually, and semiarid regions, which get from 10 to 20 inches, constitute about one-third of the Earth's land area. Any changes the planet experiences in the future could have a profound effect on these regions because there is a close relationship between these ecosystems' health and the weather and water cycle. To help measure and predict such long-term changes, scientists from nine federal agencies, eight universities, six foreign agencies, and one private organization are working together on the SALSA program.

Their outdoor laboratory is the 2,500-square-mile Upper San Pedro River Basin that spans the border between northern Sonora in Mexico and southeastern Arizona. Scientists hope SALSA will establish this basin as the North American site where remotely sensed data from satellites and aircraft, coupled with computer models that predict changes, will be calibrated and validated.

"The basin is ideal for our research; it contains climatic diversity and five distinct vegetation types over distances as short as 12 miles. The Nature Conservancy has declared the San Pedro riparian corridor one of the 'Twelve Great Places of the Western Hemisphere'," says David C. Goodrich. An ARS hydraulic engineer at Tucson, he heads the overall SALSA program, with ARS as the lead agency.

Intensive hydrologic data have been collected over the past 30 years from part of this basin, ARS' Walnut Gulch Experimental Watershed. This information will be added to that collected as part of SALSA, which began in 1995.

This year, the program will concentrate on understanding the San Pedro riparian system on the U.S. side of the border. Scientists will establish baseline data by measuring surface water, groundwater, and transpiration. They'll compare their measurements to readings collected from satellites and aircraft during five overflights through October 1997.

Over the entire basin, SALSA team members from ARS, the U.S. Environmental Protection Agency, Tennessee Valley Authority, University of Arizona, and Mexico and France will concentrate on energy balance measurements from several areas, vegetative characterization from satellites, and large-scale land cover change using ground and historical satellite data.

Scientists expect to monitor how humans change the area. "We can already see some evidence from satellite images. The U.S.-Mexico border is clearly visible because of different livestock grazing practices in the two countries. The presence and possible expansion of an enormous copper mining operation at the headwaters of the San Pedro may also have significant impact on the basin's water quality and quantity," adds Goodrich.

Future plans call for collecting and archiving information like precipitation and solar radiation from the different areas over a 5- to 10-year period. Then a basin-scale hydrological model will integrate these and other variables.

Scientists hope the effort will improve how computer models predict the impact of environmental changes on the hydrology and ecology of this and other large basins.

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