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Freshwater: Will the west run out?

Posted at 9:29 PM, Apr 04, 2016
and last updated 2016-04-05 01:29:37-04

TUCSON (KGUN9-TV) – Researchers at the University of Arizona and around the country are fairly sure about one thing for the future: dry areas will become drier, wet areas will become wetter.

In the San Pedro River valley east of Tucson, that means scientists are predicting a shrinking supply of groundwater in the future. About 40 percent of the western U.S. relies on pumping groundwater for their fresh water supplies.

Thomas Meixner, a professor of hydrology at UA, is one of the lead authors in a study published in Journal of Hydrology looking at the effect of climate change on groundwater resources in the west.

“What we wanted to understand was how climate change might influence how much water is being put into our groundwater systems on an annual basis,” Meixner said.

Meixner says Arizona is one place where it will probably become drier.

He says over the next few decades climate change could cause winter storm tracks to move further north. For example, if you were to draw a straight line from Denver to San Francisco, the areas to the north would receive more winter precipitation, but the areas to the south are predicted to receive less.

Winter rain and snow are particularly important because they are most effective at recharging groundwater resources. Monsoon rain in the summer is less predictable and contributes less to groundwater recharge.

“As a result of less winter precipitation, also results in less recharge. So what we saw in the southern tier of the west was a roughly 10-15 percent lower depending on the basin,” said Meixner. “In the San Pedro Basin we estimate as much as a 30 percent decline in recharge because of these expected shifts in climate patterns.”

By 2050, Meixner is saying there could be 30 percent less water going into the San Pedro River basin, meanwhile we are already taking more water out than goes in.

The Santa Cruz River poses as one example of what can happen if you continue to take more what out than goes back into the ground. The river used to run year round but now runs dry, except during the summer monsoon were storm runoff can fill the river. Trees used to grow around the riverbed, but not anymore. Meixner says that is the same thing that could happen around the San Pedro if nothing changes.

Water conservation is needed to help reduce the amount of water we take from the ground according to Meixner. Most water in the west is used for agriculture. On the residential side, Meixner says homes need to continue increasing efficiency.

He says in Tucson, water usage has gone down 3-4 percent every year for the past decade. While Tucson used to use about 200 gallons of water per person per day, now the city is below 120 gallons. In the residential sector it is around 90 gallons per person, and in new construction homes it is closer to 50 gallons per person per day. Meixner says we can save even more water if we continue to work at it.

"We have been consistently getting more efficient, but what I would say is there is potential to be more efficient and more conservative than we have in the past," he said.