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By Root 1893 0

water problems that bedevil Montana along with other dry areas of the American West, think of the Bitterroot Valley as having two largely separate water supplies: irrigation from ditches fed by mountain streams, lakes, or the Bitterroot River itself, to water fields for agriculture; and wells drilled into underground aquifers, which provide most of the water for domestic use. The valley’s larger towns provide municipal water supplies, but houses outside those few towns all get their water from individual private wells. Both the irrigation water supply and the well water supply are facing the same fundamental dilemma: an increasing number of users for decreasing amounts of water. As the Bitterroot’s water commissioner, Vern Woolsey, explained it succinctly to me, “Whenever you have a source of water and more than two people using it, there will be a problem. But why fight about water? Fighting won’t make more water!”

The ultimate reason for decreasing amounts of water is climate change: Montana is becoming warmer and drier. While global warming will produce winners as well as losers in different places around the world, Montana will be among the big losers because its rainfall was already marginally adequate for agriculture. Drought has now forced abandonment of large areas of farmland in eastern Montana, as well as in adjacent areas of Alberta and Saskatchewan. Visible effects of global warming in my summering areas in western Montana are that snow in the mountains is becoming confined to higher altitudes and often now no longer remains throughout the summer on the mountains surrounding the Big Hole Basin, as it did when I first visited in 1953.

The most visible effect of global warming in Montana, and perhaps anywhere in the world, is in Glacier National Park. While glaciers all over the world are in retreat—on Mt. Kilimanjaro, in the Andes and Alps, on the mountains of New Guinea, and around Mt. Everest—the phenomenon has been especially well studied in Montana because its glaciers are so accessible to climatologists and tourists. When the area of Glacier National Park was first visited by naturalists in the late 1800s, it contained over 150 glaciers; now, there are only about 35 left, mostly at just a small fraction of their first-reported size. At present rates of melting, Glacier National Park will have no glaciers at all by the year 2030. Such declines in the mountain snowpack are bad for irrigation systems, whose summer water comes from melting of the snow that remains up in the mountains. It’s also bad for well systems tapping the Bitterroot River’s aquifer, whose volume has decreased because of recent drought.

As in other dry areas of the American West, agriculture would be impossible in the Bittterroot Valley without irrigation, because annual rainfall in the valley bottom is only about 13 inches per year. Without irrigation, the valley’s vegetation would be sagebrush, which is what Lewis and Clark reported on their visit in 1805-1806, and which one still sees today as soon as one crosses the last irrigation ditch on the valley’s eastern side. Construction of irrigation systems fed by snowmelt water from the high mountains forming the valley’s western side began already in the late 1800s and peaked in 1908-1910. Within each irrigation system or district, each landowner or group of landowners has the right to take for his or her land a specified quantity of water from the system.

Unfortunately, in most Bitterroot irrigation districts the water is “overallocated.” That is—incredibly to a naïve outsider like me—the sum of the water rights allocated to all landowners exceeds the flow of water available in most years, at least later in the summer when snowmelt is decreasing. Part of the reason is that allocations are calculated on the assumption of a fixed water supply, but in fact water supplies vary from year to year with climate, and the assumed fixed water supply is the value for a relatively wet year. The solution is to assign priorities among landowners according to the historical date on which the water right