Gauging the rivers takes smart folks and brawny bytes
Flood forecasts rely on powerful computer models to crunch data for rain and snow.
By Carrie Peyton Dahlberg - Bee Staff Writer
Published 12:00 am PST Wednesday, December 27, 2006
Twice a day all winter, and more often when it's raining hard, the pulse of California's rivers is plotted on the Internet, posted there in colored charts that foretell flood or safety for anxious river watchers.
The data are used by everyone from emergency officials who help make evacuation decisions to homeowners wondering when to move their lawn furniture to higher ground.
Those who rely on the river forecasts, though, might not realize the computing brawn and human ingenuity that go into predicting river rises that are still hours or days away.
At the heart of the process is a cadre of forecasters and a pair of computer models, one developed more than three decades ago by a now retired Sacramento hydrologist who still remembers it as a career highlight.
"We weren't supposed to be involved in this task. It was supposed to be on a national basis," said Robert Burnash, who recalls sneaking the model into an international competition in Switzerland to help win the recognition he felt it deserved.
Today, the Sacramento Soil Moisture Accounting Model that Burnash and two colleagues created remains a keystone of river forecasting nationwide, said Eric Strem of the National Weather Service's California Nevada River Forecast Center.
It is one of four main ingredients that weather forecasters and hydrologists use each day to produce predictions for more than 80 locations along rivers large and small. Their work begins with two sets of information. There are rain and snowfall predictions for watersheds in three states, produced by the center's weather forecasters. And there are readings from about 600 river and rain gauges.