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What is Drought?

What is Drought?

The government officially defines drought as "a period of insufficient rainfall for normal plant growth, which begins when soil moisture is so diminished that vegetation roots cannot absorb enough water to replace that lost by transpiration."

This is a good definition for areas that depend on rainfall for their moisture, but, in Colorado, 80 percent of our surface water supplies come from melting snowpack. A better definition of drought for Colorado might read: "A period of insufficient snowpack and reservoir storage to provide adequate water to urban and rural areas."

How Dry Colorado is Right Now

Most people believe that we are in the third consecutive year of a drought cycle in Colorado and that the state is in the fifth year of below-average snow pack. Based on the available information we have now, we are in the worst drought since 1977, with some river basins below 10 percent of their normal water capacity.

The chances of recovery this year are minimal. The state's winter snowpack typically reaches its maximum levels around April 1. This leaves the state's water users hoping for good spring moisture and a strong, late-summer monsoon to help ease what's becoming an almost certain shortage of water this summer for the state.

Snowpack

Snowpack in Colorado refers to the accumulation of snow that gradually adds up over the course of the winter, mostly in the mountains. The water content of snowpack is what water officials monitor closely because it directly relates to the amount of water that will end up in Colorado's rivers, streams, reservoirs and irrigation canals during the late spring and summer.

The water content in mountain snowpack normally reaches its greatest amount in mid-April but sometimes does not peak until late April or early May. Based on average measurements of more than 70 monitoring locations in high and moderately high snow accumulation areas in Colorado's mountains, the average snowpack water content is about 18 inches at its peak. This year, the snowpack water content reached its maximum in late March, averaging about 10 inches. Mountain snow has been melting steadily since then, and, as of April 24, the statewide average snow water equivalent remaining in the mountain snowpack was 5 inches compared to an historical average on this date of about 17 inches. (This information is provided by the USDA Natural Resources Conservation Service, the administrator of the snowpack monitoring program.)

Current Snowpack Levels

According to the Natural Resources Conservation Service, the state is now at its lowest percent of average snowpack since the drought year of 1977, when the state's snowpack was only 46 percent of average. Many remember that year as a record low snowpack year in the state.

As an example, the Arkansas River basin is 48 percent of normal, which is only 57 percent of what the snowpack was last year at this time. The Arkansas basin reservoir storage is at 77 percent of normal, which is 65 percent of what it was last year.

Stream flow forecasts call for below average runoff across the state. Many streams across southern Colorado, for example, will likely show extremely low runoff, ranging from 20 to 40 percent of average.

River Basins

A river basin is simply the land area that could contribute water to a particular river by natural gravity. The South Platte River Basin, for example, consists of all the areas from the crest of the mountains (the Continental Divide in this case) to the river itself, where all water that flows naturally by gravity without evaporating would end up in the South Platte River. Thus, Castle Rock is in the South Platte River Basin as is Cheyenne, Wyoming and Estes Park, as well as the cities of Denver, Greeley, Fort Morgan and others that are immediately along the river.

Stream Flow and What It Measures

Stream flow is the volume of water passing a specified point along a river or stream. Stream flow is typically measured in units of cubic feet per second to define instantaneous flow rates, or in acre-feet to define the total volume of water over longer periods of time.

Scientists have long established useful relationships between measured snow pack levels and ensuing stream flow volumes so that winter and spring snowpack measurements result in reasonably accurate predictions of spring and summer stream flow from Colorado's mountain rivers and streams.

In Colorado's water law system, accurate measurements of stream flow are critical for determining how much water is available to each water owner. Hydrologists and engineers also track stream flow carefully in order to determine how large to build structures such as bridges, culverts, canals, dams and spillways to safely convey water from snowmelt and from heavy rains.

How  This Drought Will Affect the Average Colorado Homeowner

The water shortage affects many industries, including farmers, vegetable growers and greenhouses, as well as implications for individuals in urban and rural areas and how they'll use water. Some water users will be impacted more than others. For example, people who own land with junior water rights will be impacted by the low snowpack and runoff levels expected this summer.

Food producers, including farmers and ranchers, may be the most affected by the drought, but urban water users also will experience consequences. Water conservation is an important tool that can help preserve water during a dry year. Some strategies that all citizens can use to contribute to water conservation are to reduce their personal water use at home and on their landscapes. For more information about water conservation in the home and on landscapes, contact the local Cooperative Extension office, usually listed under the county government section of the local phone book. Information also is available at www.agnews.colostate.edu and will continue to be updated throughout the summer.

Information courtesy of CSU Agricultural News.

Photo: Judy Sedbrook

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Date last revised: 01/05/2010