Holm: Drought and disaster in Colorado
September 20, 2013
The destruction from heavy rains on the Front Range last week is truly mind-boggling: houses swept away by raging rivers, bridges gone, numerous rock slides, whole towns isolated, and countless farm fields under water. Thousands of people have had to leave their homes, and hundreds remain unaccounted for.
Looking at the rainfall totals, it's not hard to see why — some areas received nearly as much precipitation in one week as they normally receive in an entire year. And September is normally a dry month!
The silver lining in this disaster is that it has ended the drought over a good chunk of northeastern Colorado. State climatologist Nolan Doesken told the Denver Post that "Drought as we know it will be ended at a number of locations." Areas recommended for removal from drought classification include Larimer, Boulder, Gilpin, Jefferson, Lake, western Weld, Northern Park, western Arapahoe, western Adams, Douglas, western Elbert, northern El Paso, central Teller and central Fremont counties.
The flood affected the balance between water supply and demand in two ways: not only did it bring more supply, but it also decreased demand. Farmers don't need to, or can't anyway, irrigate flooded fields. Front Range water managers are banking the extra water in reservoirs, which are filling up at a time when they are normally being drawn down.
Since the Western Slope shares Colorado River water with the Front Range, reduced demands there mean less water diverted across the Continental Divide. As the storms got underway September 12, the Bureau of Reclamation stopped diversions of Western Slope water through the Colorado-Big Thompson Project, which takes water through the Adams Tunnel from Grand Lake to the Eastern Slope.
Although we've been spared the floods, the Western Slope has also been pretty wet lately — wet enough that the experts have recommended that the US Drought Monitor reclassify most of the region from "moderate drought" to "abnormally dry" conditions. Between August 18 and September 16, most of western Colorado has received at least 150 percent of average levels of precipitation for this period.
Going into the fall with nice, moist soils means that more of next year's snowmelt is likely to run off and help refill reservoirs, instead of being absorbed into the ground. Those reservoirs still need filling. As of September 16, Lake Powell was only 45 percent full, and Blue Mesa Reservoir, Colorado's largest, was just 41 percent full.
Hannah Holm is the coordinator of the Water Center at Colorado Mesa University.
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