"We don't know how climate change will affect water resources," said Jonathan Overpeck, director of the University of Arizona's Institute for the Study of Planet Earth, testified Wednesday before the House Science and Technology Committee.

Overpeck, a Nobel Prize-winning scientist, said scientists don't know how the water supply will change in the future, the Arizona Daily Star reported.

"Temperature certainly has a major effect on water supply," he said. "As temperatures goes up, there is an increase in the amount of moisture that the atmosphere can hold, so there will be more demand. It will get the water from soil, forests, agriculture, from plants, it will get them from reservoirs, from any open source of water.