That, at any rate, was the idea entertained at the turn of the century by, among others, James E. Church, an active outdoorsman who was a professor of Latin and Greek at the University of Nevada, in Reno. Church was animated in part by the situation of Lake Tahoe, which epitomized the competition for water in the West. In this case the competition involved farmers downstream, who needed the lake's water to irrigate their crops; a hydroelectric-power company, which operated several power plants on the Truckee River, whose source is Lake Tahoe; property owners on the lake, who wanted its level to remain constant; and the Paiute Indians, who by federal treaty were guaranteed a certain amount of Tahoe water to feed their Pyramid Lake. Being able to predict snowmelt would simplify the management of the lake.
Because evaluating water content was his aim, and because the water content of snow varies widely from storm to storm and even within the context of a single "weather event," Church contended that a simple depth measurement would probably not suffice. The old rule of thumb for snow-to-water conversion is that ten inches of "average" newly fallen snow make for about one inch of water, but some snow is much wetter and some is much drier. In Colorado, famous among skiers for its powder, twenty inches of snow or more may be needed to produce one inch of water. The samples that Church required in order to create a historical index had to reflect the water content, the "snow-water equivalent." Church therefore employed a stainless-steel cylinder, which he forced through the snow to extract samples from the surface of the snow to the ground. Once obtained, the samples would be weighed, weight being a reliable index of water content. Church's extraction instrument, which was more than six feet long, and onto which extensions could be screwed, came to be known as the Mount Rose sampler, after the mountain where he conducted his first surveys. Subsequent models have been waxed, polished, baked with silicon, and provided with teeth, and the stainless steel has given way to aluminum, but their design remains based on the original.
By 1911 Church and a U.S. Weather Bureau official named J. Cecil Alter were independently making systematic snow surveys, Church around Tahoe and Alter in the watershed around Great Salt Lake. They each developed the idea of the "snow course"—a series of sampling sites strung across a short distance, in order to reduce distortions caused by wind and drift. The very same sites, identified by tall markers, would be surveyed year after year, to ensure that the data were truly comparable. The surveyors' efforts were focused on the higher elevations, where there were no meteorological stations of any kind, and where, from the moment of first snowfall to the onset of spring thaw, the snowpack is less apt to melt: it is a more or less steadily accumulating resource. The altitude, though, brought problems of accessibility. Church and Alter and those who came after them had to trudge up to the snow courses on snowshoes and skis. There were blizzards to contend with. There were avalanches, and in the spring there were bears. I asked one veteran snow surveyor, Douglas Powell—a man who, as a graduate student, knew James Church, and who estimates that he has spent 1,600 days of his life in the high country on skis—if "grueling" was a word that accurately described the servicing of a snow course. He said no, the word he would use was "demanding," and he went on to tell about how once, in 1969, when he was conducting a survey in the Sierra Nevada, it snowed 150 inches in two days. Powell said, "All right, maybe grueling."
Laws unto themselves
As the idea of snow surveys caught on, promoted first by private interests and universities, then by state governments, and ultimately by the federal government, with James Church playing the proselytizing role of Saint Paul, snow courses began to spread throughout the western mountains. With them came a modest support structure. Photographs from the 1930s and 1940s show the log cabins built to sustain snow surveyors on weeklong treks through alpine country; many of the cabins were topped by a wooden tower twenty or thirty feet high—the "Santa Claus chimney." In late winter the snow would often be so high that only a door at the top of the chimney offered access to the snug safety of the cabin deep below. Besides physical comfort there was the comfort offered by a professional guild: the Western Snow Conference was established in 1933. (An Eastern Snow Conference was established several years later; its focus is somewhat less on snow as a resource, somewhat more on snow as a nuisance.)
Snow courses proliferated in the West—there were about a thousand of them by 1940—because the data they provided and the models they made possible proved useful. The models were not subtle. They were at first based solely on the amount of snow on the ground, with the data being used in an equation that was found, through trial and error, to produce a semi-satisfactory result. It was not long, however, before hydrologists realized that every basin, every watershed, worked in a different way. George D. Clyde, a Utah governor and one of the great names in American hydrology, put it this way: "Each watershed seems to be a law unto itself." Patterns of precipitation in the mountains of the Northwest turned out to be vastly different from those in the mountains of the Southwest. The assumption that the depth of the alpine snowpack greatly exceeded that of the snowpack at lower elevations proved to be correct in most places, but often not in Arizona or California. In Nevada the relationship was sometimes turned on its head: it all depended on whether storms tended to come in low or high, and on what stood in their way.
New variables had to be added. One of the first was soil moisture at the time of the first snow. If the weather had been unusually dry, much of the spring snowmelt would drain into the ground, and would not immediately show up in streamflow; unexpected shortages would occur. If it had been unusually wet, not only would most of the water in the snow cover run off but the increased contribution from water in the soil might build streamflows of a size no one had anticipated. Other factors, too, needed to be considered—elevation, wind speed, air temperature, radiation, slope of terrain, extent of snow cover, extent of tree cover, spring precipitation. As these were gradually incorporated into models, the models began to look more and more like something that aspired to show conceptually how the natural world really worked.
That process would take decades—indeed, is still going on, the state of the art currently being represented by the National Weather Service's powerful and intricate River Forecast System model. Even in their primitive state, though, snow-water forecasts were valuable. They could certainly warn of impending extremes—vast oversupply and vast undersupply. The record over the years buoyed confidence in reliability, and water commissioners took heed. Bankers reviewed the forecasts before deciding how much credit to extend to farmers. Farmers adjusted their acreage accordingly. In Utah the 1934 spring forecast by George D. Clyde indicated that streamflows in the state would run at 25 to 50 percent of normal; farmers scaled back their planting and ranchers moved their cattle to less arid grazing lands out of state, averting disaster in what would be remembered in other states as the year that brought on the Dust Bowl.
It was largely owing to the experience of 1934 that the federal government began to support and coordinate snow-survey work in the western states, and to conduct snow surveys of its own—a role the Soil Conservation Service took on in 1939 and retains to this day. The Depression era also witnessed a vast amount of spending on dams, reservoirs, irrigation canals—public works that harnessed the annual snowmelt but made forecasts of its volume all the more important. People in the eastern United States and even many in the West don't necessarily appreciate the intricate web of snowmelt-filled waterworks that makes the western United States possible. The Colorado River alone today feeds 1,470 reservoirs.
Will infrastructure-building and management of the interior ever again seem as heroic and progressive as they did during the 1930s? Life magazine, the television of its time, sent photographers to record snow surveyors on the job, following R. A. ("Arch") Work, one of the founding fathers of the SCS system, and a ranger named Jack Frost (!) as they trekked from course to course high in the Cascades. Looking back wistfully on this period, the author of one engineering textbook calls it "the First Golden Age of Hydrology."
Better data, better models
I sat down for an hour at the Snow Conference meeting with Eugene L. Peck, who is the president of a hydrological engineering firm called Hydex, and who for more than three decades was on the hydrological staff of the National Weather Service; his career there culminated with the directorship of the Hydrologic Research Laboratory. When I asked him how deep his roots went in American hydrology, he replied, "I had breakfast with J. E. Church at the meeting of the Western Snow Conference in 1950." The National Weather Service and the Soil Conservation Service, which collect snow data in different ways and cooperate on streamflow forecasts, had numerous disputes in decades past over issues of procedure and turf. Peck, who spent almost all of his career doing the basic work of hydrology in the western states—collecting data, improving models, mapping, forecasting—seems to remember them all. He may even have started a few.
I had asked Peck if he could give me a capsule history of snow forecasting in America, and he arrived with several pieces of yellow legal paper, a chronology sketched out from memory. The entries began with "1907-1910—J. Cecil Alter using stove pipe for cutter, Mill Creek nr SLC, UT" and went through "1950s—Competition between SCS & NWS, many problems but made for better forecasts," up through "1969-78—Development of airborne gamma radiation to measure water equivalent of snow cover," and kept on going.
Later Peck showed me a few items of historical interest: a half dozen delicate photographic negatives on glass, depicting snow-survey stations at Wagon Wheel Gap, in Colorado, during the 1920s; a sere and brittle copy of Volume 1, Number 1 (1920) of the Bulletin of the American Meteorological Society; a copy, preserved in a plastic sleeve, of a blue-bound pamphlet titled Snow Surveying: USDA Miscellaneous Publication No. 380 (1940), which was the first official manual for snow surveyors; and, typed on translucent onionskin paper, corrected by hand, the text of a lecture by J. Cecil Alter, "Read before the Utah Academy of Sciences, Salt Lake City, Utah, Saturday, April 3, 1926." I picked up the last of these items with a certain reverence. I felt as if I were touching one of the Dead Sea Scrolls of hydrology.
Peck, though, is no antiquarian. He is involved in, among other things, NASA's boreas project, which is an ambitious attempt to create a meteorological and hydrological portrait of large parts of Canada —-a portion of the continent whose freshwater resources in the form of snowmelt go largely uncaptured. In our conversations about snow and the water it contains Peck kept coming back to one basic point: that snowmelt forecasting still depends on having some sort of data and some sort of model to plug the data into. The story of forecasting, then, is the story of a search for better data and better models.
There has from the beginning been a school, for example, that held that data gathered from precipitation gauges—open buckets, basically—could be used to predict streamflow as reliably as data from snow surveys done with snow tubes. Snow-tube surveys did have obvious disadvantages. As noted, they were arduous. They were labor-intensive and therefore costly. And frequently snow courses were sited in areas that, for one reason or another, proved unrepresentative of the actual snowpack. Precipitation gauges were easier to get to—they tended to be at lower elevations—and could even be automated. They could provide information about rain as well as snow. But precipitation gauges had drawbacks too. Even when they were equipped with shields, for example, high winds would impel much snow laterally across the orifice, in a process called eddying. The result was "undercatch": the gauges would underreport the volume of snow.
Precipitation gauges, too, can be sited in unrepresentative areas, a problem occasionally abetted by human agency. Peck told the story of the weather station in Shoshone, Colorado, whose precipitation-gauge data had been so erratic and variable that Peck, who at the time was the head of the National Weather Service's water-supply forecast unit, in Salt Lake City, decided to visit the place and talk to the man who had run it for years and years. "I found the can," Peck said. "It was hooked onto a metal stairway where the snow could slide into it off the roof. But precip couldn't get in there, it was up so close to the building. So I said to the old guy, 'Well, how long's it been there?' And he said, 'Actually, quite a while. You know, originally it was out by the highway, in the thirties.' And I said, 'What happened?' And he said, 'Everything went fine—it really was a good place—except when the snowblowers on the highway began blowing snow over it and it started filling up. So we decided to move it. We moved it behind the station, but the tree grew up and was covering it. So we moved it up by the school ground. But that didn't work too well, because we started getting precipitation when there was no precipitation. Kids were using it for a urinal.'"
Beginning in the 1960s, Peck went on, forecasters began experimenting with a device called a snow pillow. A snow pillow looks like a very large ravioli made of neoprene rubber or pliable metal. It is a square, perhaps six to ten feet on a side, and is filled with antifreeze. As snow falls and the snowpack gets heavier, the pillow is compressed; the degree of compression, reflecting the weight of the water above, is communicated by radio to a monitoring station. One great advantage of snow pillows is that they can be placed securely in remote locations, where they will transmit data throughout the winter. But they are prey to a variety of ailments. One is called "bridging": periods of thaw or rain followed by a freeze can result in the creation of a reinforced support layer or even a static frozen dome over the pillow, which effectively tricks it into thinking that no further accumulation has occurred when it has.