July Drought Update: Monsoon Season Could Lessen Impacts of Summer Drought; Flash Flooding Becomes a Major Concern

As Colorado’s drought conditions worsen and the state’s water supplies continue to diminish, climate researchers at the Colorado Climate Center at Colorado State University note that some limited relief may be in sight.

With the climatologically expected onset of the annual monsoon rains, portions of Colorado could experience an increase in precipitation over the next few weeks. However, the researchers warn that summer rainfall is often localized and not widespread, lightning from monsoon thunderstorms can start additional fires and flash flooding can easily occur in recently burned areas.

"The anticipated monsoon rains will not end Colorado’s drought, but an active summer thunderstorm season could bring some relief from dryness in the region," said state climatologist and professor of atmospheric sciences Roger Pielke Sr. "However, with summer rains come lightning, and much of the state is susceptible to lightning-triggered wildfires. Additionally, weakened soils stripped of vegetation from recent fires are incapable of preventing flash floods caused by heavy rainfalls, potentially leading to an entirely different set of problems for those areas."

Serious drought continues to cover Colorado as the state measured one of its driest periods from December to May in 107 years of record keeping. Typical of drought years, temperatures across the state have been hotter than average; since early June, parts of Colorado have remained up to six degrees above long-term averages. The continuation of hot, dry weather keeps fire indices in the very high to extreme range throughout Colorado. However, NOAA’s outlook calls for short-term improvement through September for much of the central Rockies due to summer thunderstorms.

June precipitation totals for the state were below average, ranging from little or no precipitation over much of western Colorado and the mountains to near and above average moisture for some areas on the eastern plains. A few limited locations throughout the state received relatively heavy rainfall from thunderstorms: the town of Genoa, east of Limon, measured 4.35 inches in June and approximately 3 inches of rain fell near Greeley during the first week of July. However, the moisture at those areas quickly evaporated. Overall, June marked the ninth consecutive month of below average precipitation for Colorado.

This year’s snowpack, Colorado’s lowest accumulation in decades, melted out across most of the state in May, approximately two months earlier than usual. According to the Colorado Division of Water Resources, the availability of mountain-based water supplies, or runoff, from the Colorado, Yampa/White, and San Juan/Dolores River basins has essentially bottomed out. Supply conditions in the Arkansas River basin are also very low. Accordingly, record low streamflow volumes continue throughout the state.

The low June runoff, in which reservoirs throughout Colorado were not replenished, combined with the recent dry weather placed heavy demands and reservoirs which are being depleted at an unusually rapid rate for this time of year. Statewide storage decreased from 86 percent of average on May 1 to 73 percent of average on June 1 to 59 percent of average on July 1. Storage supplies in many irrigation reservoirs could be completely depleted by the end of the watering season without heavy rains and continual water conservation efforts.

The Colorado Climate Center, housed in Colorado State University’s Department of Atmospheric Science, provides information and expertise on weather and climate patterns for the state of Colorado. Pielke and Doesken issue mid-month Colorado drought advisories throughout the spring and summer in conjunction with the center’s new Web site at http://ccc.atmos.colostate.edu that provides access to current drought, weather and other climate data.