Report: Colorado flooding was 'unprecedented'

Doyle Rice | USA TODAY

Show Caption Hide Caption Colorado flood repairs hinge on government funds Local governments in Colorado expect to get money from the state and federal government to help rebuild from the floods, but the speed of rebuilding may depend on how quickly that money gets here.

Flooding probably unmatched in at least 35 years

All-time record rainfall was recorded

Many spots picked up more than a foot of rain in a week

Some of the flooding that ravaged Colorado earlier this month was "unprecedented," according to a preliminary assessment issued by government and university scientists Wednesday.

The report was prepared by the Cooperative Institute for Research in Environmental Sciences (CIRES) in Boulder, Colo. The institute includes scientists from the National Oceanic and Atmospheric Administration, the University of Colorado and Colorado State University.

"In the context of the entire Front Range this was a rare precipitation event, especially for September, and in some respects unprecedented," the assessment states.

Across the state, the floods killed at least eight people and damaged or destroyed as many as 2,000 homes. It also washed out hundreds of miles of roads and left many small mountain towns completely cut off. The floods caused damage across nearly 2,000 square miles.

The event "was likely a 100-year flood (or more accurately: a 1% probability per year flood)," the report states, and that all-time record or near-record precipitation was recorded during the week of Sept. 9-15 across the Front Range. The Front Range is a mountain range of the Rockies that runs north-south from southern Wyoming to central Colorado and includes Denver, Boulder, Fort Collins and other cities.

Many spots picked up more than a foot of rain, with one location in Boulder seeing a 16.9-inch deluge. These are totals that "have been observed in only a handful of events on the Front Range in the past century."

"The extraordinary rainfall in this event was due mainly to the unusual and persistent weather pattern that funneled abundant moisture towards the Front Range," according to the report.

Could climate change have played a role? "The most plausible influence of climate change that we can see is making slightly more water vapor available for precipitation," said Jeff Lukas, a CIRES researcher, at a news conference Wednesday. The report notes that research is underway to determine how human-caused climate change may have influenced this event and whether the risk of similar future events will increase.

Whatever the cause, the report concludes by noting that "total societal exposure to flooding on the Front Range has increased in the past several decades due to population growth and development."

Almost 4.5 million people live in or near the Front Range of the Rockies, according to the U.S. Census Bureau. This is an increase of almost 1 million people since 2000.

Contributing: Trevor Hughes, USA TODAY