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Climate Change & Water Resources

Introduction

As Montanans, we are acutely aware of water as an essential resource. The availability of adequate water supplies influences all sectors of the Montana economy. At the same time, Montana’s lakes, reservoirs, and streams provide a priceless recreational and aesthetic resource. Montanans are rightfully concerned that climatic changes will affect our historic accesses to this precious resource.

The Montana Constitution is clear that all of the state’s water resources belong to the state in behalf of its citizens. Water rights holders in Montana do not “own” water; rather, they have a right to “use” water within the guidelines and laws of the state. Water use in Montana is generally classified as consumptive – beneficial diversions or withdrawals for irrigation, livestock, industrial, or municipal purposes. A second instream classification is for beneficial non-consumptive uses of water left within streams. Examples include stream flows reserved for fish and wildlife habitat, navigational and recreational purposes, and hydroelectric power generation.

Most of Montana’s roughly 950,000 citizens live in the intermountain valleys of western Montana, along the Yellowstone River Valley in south-central and eastern Montana, and along the Missouri River in north-central and eastern Montana. Although some of northwest Montana’s mountains receive nearly 100 inches of precipitation per year, most populated regions ordinarily receive 10 to 16 inches per year. Geographically, most of the state is considered semi-arid. Periodic drought cycles compound Montana’s natural precipitation profile.

Still, Montana is a headwater state, a freshwater resource for the state, downstream states, Canadian provinces, and other water jurisdictions. And while Montana is a heavy user of water, particularly for agriculture, much more water passes through our borders than is used within the state. Consequently, climate changes that affect Montana’s water resources reach far beyond our borders.

The water resources of the state arrive principally through precipitation, much of which is stored into the summer months as mountain snowpack. Some is brought into the state as streamflow from portions of the upper Yellowstone River Basin in Wyoming and the Milk River watershed out of Canada. About 35 percent of the spring runoff in the year 2000 originated in the out-of-state portions of these basins. The upper basin of the Columbia River also delivers water into Montana, principally via the Kootenai River into Lake Koocanusa, impounded by Libby Dam. The North Fork of the Flathead River and a few streams along the Missouri also originate in Canada.

Water leaves the state largely via streamflows of the Yellowstone and Missouri River Basins (Gulf of Mexico) and the Upper Columbia River Basin and the Clark Fork River Basin (Pacific Ocean). A small quantity is delivered to Hudson Bay from Glacier Park’s northeast quadrant. Montana has about 50,000 miles of year-round streams. Underground aquifers also move water into and out of Montana’s borders. And, of course, a large quantity of water is transported through evaporative processes from surface water and land as well as plant transpiration processes.