AlQa'dah 9, 1434, Sep 15, 2013, SPA -- Successful search and rescue operations Saturday in the western US state of Colorado helped lower the number of missing people following devastating floods in a multi-county area north and north-east of Denver, DPA reported. The number of people who were unaccounted for stood at 172 Saturday, down from 218, CNN reported. It is expected to continue to shrink. One of the worst-affected areas was Boulder, a city with about 100,000 people at the base of the foothills of the Rocky Mountains and about 40 kilometres north-west of Denver. The floods have claimed the lives of four people, officials confirmed. "Given the destruction, there is a high probability" of more fatalities, Pelle said. Authories posted evacuation orders and asked people to avoid driving and being out in areas where water is rising. "Stronger thunderstorms could produce up to an inch (2.5 centimetres) or more of rain in less than 45 minutes in a few locations," the weather service said. Governour John Hickenlooper warned that an extensive recovery period is ahead for the affected area.