A report detailing the impact of climate change on the United States calls for decreased rainfall in southwestern states, with more 100-degree Fahrenheit days.

Evan Mills and Michael Wehner at the U.S. Department of Energy's Lawrence Berkeley National Laboratory contributed to the report released by the multi-agency U.S. Global Change Research Program.

For southwest states, which include California, the report forecasts a hotter, drier climate with significant effects on the environment, agriculture and health.

"This is the most thorough and up-to-date review ever assembled of climate-change impacts observed to date, as well as those anticipated in the future across the United States," Mills said.

The report addresses nine U.S. zones -- Southwest, Northwest, Great Plains, Midwest, Southeast, Northeast, Alaska, U.S. islands and coasts.

"Even in areas where precipitation is projected to increase, higher temperatures will cause greater evaporation leading to a future where drought conditions are the normal state," Wehner said.

"Floods and droughts are likely to become much more common and intense as regional and seasonal precipitation patterns change and rainfall is more concentrated into heavy events with longer dry periods in between," the scientists said, adding there will likely be less snow, with more winter precipitation falling as rain.

Increasing air temperatures in parts of California's southern areas and in western Arizona could exceed 120 degrees Fahrenheit.

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