Six degrees of... devastation?

Forget the Y2K bug. Here's a real 21st-century crisis facing the Northwest: the coming drought years.

For once the headline on the press release actually understated the story beneath. "Projected snowpack decline could mean drastic changes for region," read the announcement about a paper presented June 4th by two University of Washington scientists to a meeting of the American Geophysical Society (read the paper). But the research by Dennis Lettenmaier and Alan Hamlet of the U's Civil and Environmental Engineering Department wasn't just bad news for ski-area owners. It also bodes big changes for the rest of the 12 million people who dwell in the Pacific Northwest.

Based on sophisticated computer climate models from England and Germany, the UW study predicts what's likely to happen to snowpacks and stream flows in three states and one Canadian province over the next 100 years, and its results are expressed in charts and graphs hard for an average reader to decipher. But it's clear at least that Northwest residents and transients, too, like salmon returning home to spawn, will no longer be able to take for granted that water will be there when and where they need it.

Another model, devised at a lab closer to home, goes farther and spells out just what we're likely to be in for climate-wise. According to Ruby Leung and her colleagues at the Department of Energy's Pacific Northwest National Laboratory in Richland, by the year 2080 the state of Washington will be experiencing:

* Average summer temperatures two degrees higher than at present,

* Average winter temperatures three to five degrees warmer,

* A rise in the average snow line from around 3,000 to over 4,000 feet, with a consequent

* 50 percent decrease in total average winter snow cover statewide, with a

* 50 to 90 percent decrease in the mountain snowpack below 4,000 feet.

At first glance, that doesn't seem like such hot stuff: bad news for winter sports fans, sure, but how much impact could a couple of degrees of warming have down here on the flatlands? An awful lot, unfortunately. You don't notice five degrees one way or the other when the temperature's in the 50s or 60s or even 70s. But the difference between 85 and 90 or 29 and 34 is not just noticeable, it changes the ground rules for life in these parts, threatening signature ecosystems (the Olympic rain forest) and key industries (the Skagit delta's bulb farms, Eastern Washington's orchards) while encouraging species we're currently happy to do without (mosquitoes, disease-bearing ticks).

People are flexible by nature. Other animals and plants are downright cranky about what conditions they prefer. A shift of a couple of degrees can make it too hot for a tree or plant to germinate properly, or for the bug which pollinates it to reproduce. That doesn't mean that all the hemlock trees or honey bees suddenly drop dead; it does mean that they shift their favored base of operations. Deciduous trees penetrate further up the mountain slopes, while conifers move in on rocks where previously only lichens grew. Ponds dry up. Sage moves in on meadowlands.

Thanks to generations of botanists like the UW's Estella Leopold collecting and cataloging the pollen of long-departed vegetation from lakes and bogs, we know a lot about what kind of vegetation flourished where and when in the ancient Northwest. The sparse grass and scrubby shrubs of glacial-age Puget Sound indicate that when human beings first moved into the neighborhood some 12,000 years ago, conditions were not only a lot colder but considerably drier as well. As things warmed up over the next 5,000 years or so, rainfall increased, too. Both reached peaks about 4000 BC, when winters were colder and summers warmer than today, then fell gradually as temperature extremes narrowed toward present temperate conditions.

The trouble with predicting the effect of the warming Leung's model suggests is that it has no precedent—at least since the Eocene era some 50,000,000 years ago, when, geologically, the Northwest was only just rising from the sea. But you don't need precedents to see where the predicted climate change will first impact the human ecology of the Northwest.

Since hunter-gatherers squatted beside the rapids waiting for the salmon, people in this part of the world have lived their lives in accord with the delicate balance between each winter's snowfall and the next summer's run-off. Every Northwest river has its own typical annual high- and low-water curve, but all exhibit the same general pattern: low stream flow in February, when cold locks up most precipitation in snow and ice, rising to a sharp peak in early June, when up to six times as much water fills their beds. Since early in this century we've invested incalculable billions of dollars in the form of dams to exploit this pattern—to generate hydroelectric power, support irrigated agriculture, quench the thirst of factories and cities.

Unfortunately, according to Leung's results, the pattern is almost certain to change. Even assuming that "global" part of "global warming" doesn't impact total precipitation over the region—the models aren't yet advanced enough to say much about that—warmer winters mean lower snowpacks and more rapid winter runoff, leaving less total contribution for stream flows in summer. The whole curve flattens out, and peak runoff comes earlier in the year. Our present system, elaborate as it is, still depends on mountaintops more than reservoirs for storage. "If you lose the snow storage, you need storage from somewhere else," Lettenmaier told his Boston audience. "But from an environmental standpoint, no one is ready to run out and build more dams."

When it comes to water, the first thing a city dweller thinks about is what comes out of the tap. Most western Washington water supplies depend on snowpack for storage as much or more than the drier parts of the Northwest, but despite the stunning population growth rates of urban areas around Puget Sound, urban water companies are planning well ahead to deal with shortages.

Plans are well advanced for making it possible to draw down Seattle's reservoirs on the Cedar and Tolt Rivers to levels currently impracticable, in effect increasing total annual storage without raising the dams. An "intertie" between Seattle's system and Tacoma's (fed by the Green River) to stabilize supply and demand over a larger area is about to go operational. An aquifer in West Seattle can already be drawn upon in emergencies; water department engineers are looking into the possibility of pumping water into it in the wet season, in effect creating a subterranean reservoir without the negative environmental impact of subaerial ones.

Things aren't so simple for the Corps of Engineers and their vast system of multipurpose dams on the Columbia and Snake. A shift in peak stream flow to April or May from June is likely to play havoc with the Corps' half-formed plans to better accommodate salmon runs, as well as with the runs themselves—there being no effective way to notify the fish that spring will be arriving a month earlier in the future.

Least affected by the change may be the dams' power-generation function. Indeed, as City Light deputy superintendent of power management Paula Green points out, the shift in stream flow patterns could actually be of benefit. "Since our peak time for power consumption is the winter, it could mean we actually have more power when we need it, and more power to sell to other regions of the country if we don't need it." (Unfortunately, that could change in a hurry if summers heat up by the full five degrees suggested by the model and people find that they can no longer live without air conditioning.)

Agriculture is probably the area most directly affected by the coming warm-up: not so much by heat directly (it's already damned hot in August in eastern Washington) but by drought. Farmers need water between April and November, and every additional gallon flushed downstream from November to April because the reservoirs behind the McNary, Potholes, Grand Coulee, and Ice Harbor dams are too full to hold it is a gallon unavailable six months later when it's needed.

No matter how low the Columbia runs, it's still got a lot of water. Much of the state's irrigation water doesn't come from the Columbia, however, but from smaller streams fed directly by snowpack: the Wenatchee, the Yakima, the Okanogan. Some eastern Washington watersheds, like that of the American River, a tributary of the Yakima, are already used beyond their capacity. Lower flows could severely impact the state's orchards and vineyards.

What Leung's model can't predict is whether total rainfall will go up, down, or redistribute itself under the new regime. In some areas of North America, the rise in temperature may well affect rainfall, but out here on the edge of the continent, precipitation is determined by what's happening in and over the 5,000 miles of open ocean to the west of us: the periodic swing from (dry) el Ni�o (wet) la Ni�onditions.

Curiously enough, a City Light study going back over 50 years of snowpack records shows no significant regionwide difference between the two poles of the pattern. If anything, says the UW's Lettenmaier, current models actually show an increase of precipitation over the next 50 years. "When the ocean surface warms up, more water evaporates, which makes the whole world heat engine run faster. The atmosphere can't store significantly more water vapor that it does already, so if there's more evaporation, there's going to be more rainfall."

Somewhere, but not necessarily here. One of the most frustrating things about the current projections for future Northwest climate is that we can't be sure just how they'll play out in practice. There's no exact historic precedent. The UW's Leopold suggests that the best prediction may lie in information from 10,000 years in the past. "Nine or 10 thousand years ago, the earth's orbit was configured so the Northwest was experiencing its maximum summer exposure to the sun. Climate was more 'continental': hotter in summer, colder in winter. Northwest forests were a lot different back then. Instead of cedar and hemlock you had mainly Douglas fir and fairly open woodland without a lot of undergrowth, broken by prairie. The San Juan Islands seem to have still exhibited this pattern when the first white settlers arrived. Fire was important in maintaining that pattern."

The orbital cycle which brought us that pattern has just reached its opposite extreme, with summer and winter insolation as close to being in balance as our latitude allows. Now we start the 9,000-year crawl back to square one—this time with human-generated greenhouse gases to complicate an equation that was already complicated enough.

A good guess at what the climate might be more than 50 or 100 years ahead may well be unattainable, no matter how big and fast computers get (see "A model climate," below). The same problem that prevents us from predicting whether a particular asteroid will strike the earth 500 years from now prevents weather forecasts that far ahead: A miniscule error in the input of today's equations can grow in the course of a few billion iterations to the point that the resulting prediction is hopelessly misleading, if not pure nonsense. Given what we know now and can safely guess about the future, however, it's a safe bet that it's going to get warmer. Whether it'll be fair and warmer, we'll have to wait and see. But children born today will know the answer before they're old.

A model climate

Everybody knows what distinguishes "weather" from "climate." Weather is unpredictable: It's what ruined the picnic last weekend. Climate is the general scheme of things, subject to variation and occasional extremes, but always drifting back toward a norm—which around here means mild, overcast, wind from the west, chance of showers.

It was more than a century and a half ago that scientists began to realize that, on a long enough time scale, climate is as variable as weather: that Earth's climate has been constantly changing ever since the planet cooled enough to allow liquid water to collect on it. (The evaporation and recondensation of water, absorbing heat at one point on its surface and re-releasing at another, drives the whole weather process.)

Most of the evidence for global warming has emerged from careful analyses of world weather records stretching back a few centuries: squeezing out the "noise" of random variation in the stats to let the long-term trends emerge, and then extending the trend discovered into the future. But recently more sophisticated techniques for modeling climate 50 or 100 years hence have begun to emerge.

Climate modeling is a game played on supercomputers. There's no arcane mathematics required, just unimaginably vast number-crunching capacity. Climate modelers first break up the map of the region under study into rectangular blocks. Each block is assigned a set of numbers representing climate data—some fixed, like elevation, others variable, like temperature and air pressure. Then the computer calculates the impact of each number in each block on all the numbers in all the adjacent blocks. When the results are calculated, the computer updates all the variables in each block accord-ingly and repeats the process, this time based on conditions an hour (or six minutes) into the predicted "future." And repeats it again. And again. And again.

Every climate model involves trade-offs. If, to increase precision, you want to recalculate the state of the system 10 times an hour instead of once and still get a result within your lifetime, something has to give: usually the geographical "resolution" of your model. Early models resolved the earth's surface into blocks eight by 10 degrees on a side. In our latitudes, an eight-by-10 block is about 600 miles east to west by 400 miles north to south. At that resolution, the wildly varied relief of the northwest US comes out one big dull bump: not much use for predicting snowpacks and stream flows. And it still takes weeks or months to crank out those crude results.

The most sophisticated models are now down to four- or five-degree resolution: still not ideal, but four times better than 10 years ago and good enough to get an idea how changing temperatures of air and sea will impact the precipitation patterns that drive the annual round of life in the Northwest.

The modelers don't just plug in today's values, set the software running, and hope that the results will reflect reality. They generally start the model running with known data from 10, 20, or 50 years in the past. If the numbers it spits out as it chugs past the present match up pretty well with present conditions, they have better reason to trust what it will say about the future.

 
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