The idea that the San Pedro could be representative of other rivers across the nation is one of the reasons why it has become one of the most heavily-researched river systems in the nation, maybe even the world, said Thomas Maddock, head of the University of Arizona Department of Hydrology and Water Resources.

"I think the climate's probably going to hit it the hardest, although ultimately the groundwater pumping will be the real issue," he said.

But Maddock and Thomas Meixner, associate professor in U.A.'s hydrology department, said getting people to recognize that groundwater pumping is a problem might prove difficult.

"One of the struggles convincing people that the pumping will, sort of, take out the river, if you will, is that it won't happen today," Meixner said. "It's going to be a very subtle, gradual shift."

Robert Webb, a soil scientist, hydrologist and ecologist with the U.S. Geological Survey, has tracked groundwater records along the river.

"We have to ask ourselves: what is the best use of the land?" he said. "There are two ways people are extracting water from the San Pedro — diversion of surface water and pumping ground water from the thousands of wells right along the river. It's going to come down to value of what's more important along river. Is it people or agriculture, agriculture or ecological system or can we all get along? That's the question we're facing."

Maddock said it's inevitable that decreased stream flow will eventually lower the water table.

When those tables drop to a certain point the San Pedro will cease to exist.
"To maintain the treasure that is the San Pedro River Valley we must maintain the groundwater tables," said Russ Scott, a research hydrologist with the U.S. Department of Agriculture who has monitored the river at sites near Tombstone. "But there's a problem in a sense that more water is being taken out than there's going in. In time, the effects are going manifest."

Although the system is changing, researchers say the San Pedro River Valley's fate isn't set in stone.

"It depends on what people do for one thing," said Juliet Stromberg, an Arizona State University life sciences professor. "It depends on population growth and how people change their actions in terms of recharge and pumping. Effects from climate change remain uncertainties but just how severe the change will be depends on how humans manage that."