If scientists are right, changes in the Northwest climate will make water more scarce than it is now. So you would think that leaders convinced by the climate models would do something to increase the supply, but they’re not.

During most years the Northwest gets plenty of rain and, in the Cascades, snow. The runoff from snowmelt then is stored in underground aquifers in the Cascades, and during the dry season it seeps out, keeping the creeks and rivers fuller than they otherwise would be.

The theory is that climate change will diminish the amount of snowfall in the winter, and this will translate into less water available in the dry season of summer and early fall.

Writing in the Portland Oregonian, a Corvallis-based researcher with the Forest Service, Gordon Grant, says one of the implications is that this region “likely will experience diminished late-season flows and possible increased demand, placing further stress on existing water supplies for municipalities, agriculture, industry and aquatic systems.”

Oregon officials usually respond to such warnings by calling for more conservation and efficiency in water use. Which makes sense, but:

Oregon’s population now is about 3.8 million, roughly two-thirds of it in the Willamette Valley and the metro area. State economists predict continued population increases despite the current economic slowdown, to more than 4.1 million in 2015. That’s an 8 percent increase over the next seven years. So even if the population in general could reduce individual water needs by 8 percent by that time, we still would consume the same amount of water as now.

The population is expected to keep growing well beyond 2015, so there’s every reason to believe that the need for water will not go down but up instead.

If the streams provide less water in the dry season, and more needs to be left in them for wildlife and water quality, while the population needs the same amount or more, where are we going to get the extra water?

The answer you never read anything about is more wintertime storage. That means additional impoundments among the headwaters of the streams that feed the Willamette from the Cascades.

The most likely sites for storage dams have all been used or, if they were once considered and authorized by Congress, de-authorized since then because they were judged uneconomical.

But for the population of the Willamette Valley, the future is endless. And what was considered unnecessary or uneconomical in the 1970s and ’80s may have to be revisited in the coming teens, ‘20s and ’30s and beyond.

Unless human behavior undergoes a drastic change, the need for more water storage dams may even trump considerations of wildlife if and when the valley is fuller of people with their pools, washers, showers and bathtubs — much fuller than it is now. (hh)