Fact or fiction?
Thursday, March 12, 1998
California is still reeling from El Ni¤o-related storms which caused over $400 million worth of damage to homes, businesses and roads throughout the state. But it could have been a lot worse, say long-term weather forecasters from the National Weather Service in Washington, DC.
If emergency and water officials had not had long-term weather forecasts this summer warning them of the impending El Ni¤o storms, losses could have been much greater. The ability to accurately predict future weather--an evolving and increasingly important science--enabled them to shore up levees, train volunteers, and be ready when the rain began to fall.
"It''s abundantly obvious that this information has had an enormous economic benefit and has saved lives and property," says Bob Livezey, a climatologist with the National Oceanic and Atmospheric Administration''s (NOAA) Climate Prediction Center.
While scientists couldn''t predict a year ago the intensity of this winter''s storms, they said with confidence this summer El Ni¤o was on the way. Livezey says this year''s El Ni¤o predictions were the most accurate in the history of long-term prediction.
Over the past five years, the science of long-term weather prediction has taken a leap forward in accuracy. This is attributable to two new developments. The first, the comparison of three different, independent measuring methods: two statistical models measuring worldwide ocean and land temperature fluctuations, and one global computer model which measures Pacific Ocean temperature. The smallest change in surface temperature--even half a degree--is enough to cause major changes in weather patterns worldwide. When the models all agreed this summer, scientists knew they had a big El Ni¤o event coming.
The second change in long-term forecasting is a greater insight into how to analyze historic weather data, especially past El Ni¤o phenomena. Many long-term prediction models take weather data gathered for the past hundred years and extrapolate what the weather will do in the future. El Ni¤o years are by far easier to predict than years with no extremes.
NOAA uses a Cray-90 supercomputer to crunch worldwide weather data it gathers from satellites, buoys, 10,000 human weather observers, and historical data. Each measured geographic area gets entered as a "cell," a square area like a pixel, creating a giant puzzle of the globe. Then, using equations based on thermodynamic principals, complex models are set into motion to chart the interactions of air and ocean surface temperatures and air moisture between each of the cells.
From this information come maps that chart the probability of above- or below-normal precipitation and temperatures across the globe for the next 13 months. These are updated every two months. NOAA''s 1999 prediction budget is $200 million, some of which will be spent on a faster supercomputer.
The National Climate Prediction Center sends long-term reports to hundreds of public agencies, farmers and media outlets around the country. The list of their clients include the US Department of Agriculture, the Federal Emergency Management Agency (FEMA), the US Department of the Interior, and state transportation departments.
Spokeswoman Stephanie Kenitzer anticipates long-term weather reports being used to help large entities such as transportation, energy utilities, trucking companies, agriculture, and social services coordinate emergency preparedness efforts. "I hope long-term forecasts can eventually help mitigate the social and public health impacts of weather-related disasters by encouraging preparation," says Kenitzer.
How do these agencies use the information? FEMA provides disaster relief to victims after a disaster occurs. This is the first year it used long-term weather reports in its planning when it stepped up its disaster preparedness training activities. However, Ken Nauman, a mitigation specialist for FEMA, says the agency is limited in what it can do ahead of time. "We are event-based," he says. "We can''t pre-plan."
The Monterey County Water Resources Agency (MCWRA) continually gathers data from 55 electronic rain gauges and river monitors which include the Pajaro, Salinas and Carmel Rivers. From this information the National Weather Service determines whether to issue flood and other warnings.
This fall MCWRA took El Ni¤o predictions seriously and gave its flood control and monitoring systems a checkup. Hydrologist John Stremmel says the agency also stepped up its training efforts in July. "We had extensive training of monitoring staff, we put in three more monitoring sites, and we did maintenance on existing systems. We also had practice drills with the Office of Emergency Services."
This winter''s storms are enough to sell Stremmel on the legitimacy of long-term forecasting. He says El Ni¤o is expected to hang on until late in the year, and next year looks like it''s shaping up to be a "La Ni¤a" year, a pattern that usually follows an El Ni¤o year, bearing colder temperatures and normal to less-than-normal rainfall. But in spite of the accuracy of the El Ni¤o forecasts, scientists agree, non-El Ni¤o year weather is much harder to predict way ahead of time. Most farmers look at shorter-term predictions to plan their crops, and the Monterey office of the National Weather Service only deals in 2-5 day outlooks. The Monterey office has recently secured the use of an airplane and a mobile Doppler weather radar unit to monitor El Ni¤o storms in this area.
A famous 1980 tree ring study by Harold C. Fritts and Geoffrey A. Gordon of the University of Arizona, Tuscon showed California has had droughts lasting for hundreds of years in the distant past. In the 1700s, several Native American tribes left California during a 70-year drought. Given our state''s propensity for extreme weather fluctuations, it seems likely long-term weather predictions will come into greater use as the technology improves.
Still, short-term forecasts have turned out to be wrong, and long-term predictions are an even riskier proposition. "At least we''re brutally honest when we aren''t confident of our predictions" says climatologist Bob Livezey. "We''ll always say when we''re unsure." NOAA spokeswoman, Stephanie Kenitzer says long-term prediction as a science is ".not in its infancy, but it''s still a toddler." The forecast for 1999 is now available on the World Wide Web.
Livezey says there are four factors the agency can use to boost the accuracy of its predictions. The first is El Ni¤o years, because they provide more definite patterns. The second is insight into long-term trends--decade-to-decade changes, the kind used to chart global warming. Using a decade''s worth of data, scientists can extrapolate the next 10 years. Third is the atmosphere in the North Atlantic. The temperature fluctuations there can help predict global weather patterns. And finally, physical factors, such as soil moisture content or snow covering a large area of land can be used as indicators.
In the next few years, meteorologists will be able to tell us what the weather might be, not tomorrow, but 10 years from now. Who cares whether it will be rainy in the year 2008? Given the strength of storms this winter, the answer could be, all of us.