WASHINGTON - Human activity such as driving and powering air conditioners is responsible for up to 60 percent of changes contributing to dwindling water supplies in the arid and growing West, a new study finds.

Those changes are likely to accelerate, says the study published Thursday in Science magazine, portending "a coming crisis in water supply for the western United States."


The study is likely to add to urgent calls for action already coming from Western states competing for the precious resource to irrigate farms and quench the thirst of growing populations. Devastating wildfires, avalanches and drought have also underscored the need.

Researchers led by climate expert Tim P. Barnett at the Scripps Institution of Oceanography at the University of California, San Diego, studied climate changes in the West between 1950-1999. They noted that winter precipitation falls increasingly as rain rather than snow, snow melts faster, river flows decrease in summer months, and overall warming is exacerbating dry summer conditions.