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January 17, 2002
CLIMATE CHANGE MAY BRING MORE WINTER FLOODS, AND A DRIER GROWING SEASON IN CALIFORNIA
A new study finds that climate warming over the next century will bring potential flooding in winter, as a result of increased streamflow throughout California. The study also finds less water would be available during the summer months.
Norman Miller and Kathy Bashford of Lawrence Berkeley National Laboratory (LBNL), and Eric Strem of the National Weather Service's (NWS) California-Nevada River Forecast Center looked at two climate change scenarios projected out to the year 2100. Based on these scenarios, they determined how the smallest to largest expected changes in regional temperature and precipitation would affect streamflow throughout California.
The two scenarios, both warmer and wetter than present day, were based on findings from the 2001 Intergovernmental Panel on Climate Change (IPCC) report. The report predicted temperature increases by as much as 9° Fahrenheit (F) with potential localized fluctuations in precipitation throughout the 21st century. The researchers evaluated climate change projections for three time periods; 2010-2039; 2050-2079; and 2080-2100. The projections included increases in temperature between 2.7°F (or 1.5° Celsius (C)) to 9.0°F (5.0°C) and changes in precipitation from 0.0 to 30.0 percent.
Miller and his colleagues used the precipitation and temperature data from the climate change scenarios as input into the NWS "River Forecast System," which is comprised of computer models that can simulate river flow, soil moisture and snowpack.
California's wet season stretches from December to March. In general, regardless of changes in precipitation during this period, the results showed snowmelt driven watersheds will experience increased streamflow up to 2 months earlier in the year, depending on the elevation of the watershed.
One of the main reasons for this is that global warming will reduce the number of freezing days in the season, increase early melt, and decrease the seasonal snow storage. "The results suggest that 50 percent of the season runoff will have occurred early in the year for many snow melt driven watersheds in the west," says Miller "and the resulting early snow melt implies higher streamflow increases and an increased likelihood of more flood events in future years."
Projections of water flow are based on the amount of snow the mountainous areas get in wintertime, evident by the snowline, and the timing of the snowmelt. Precipitation in the western U.S. is primarily a winter phenomena, and in California, April 1st has been established as the date for determining the amount of water resources available for the growing season.
To understand how future climate change will impact water resources, it is important to understand historical climate. The researchers looked at data from 1963 to 1992 for annual high river flow and ranked them. They then applied the same technique to future climate river flows and found the likelihood of high annual flows increased. They concluded that some increased flooding could be expected regardless of the future climate outcomes, location or elevation of watersheds.
Currently there is a coordinated study underway between LBNL and the NWS to incorporate new remotely sensed satellite data with real-time flood forecasting to reduce the risks associated with floods. Miller and his colleagues used a similar approach to successfully predict the 1995 floods of the Russian River in northern San Francisco Bay area 48 hours in advance. "By having better data, we'll be able to reduce flooding disasters in the future," Miller said.
This work was partially supported by NASA, the California Water Resources Research and Applications Center and by a grant through the California Energy Commission.
For more information:
http://www.gsfc.nasa.gov/topstory/20020117califclimate.html
Editor's Note: This session, J8.9, will be given on Thursday, January 17, 2002, at 11:45 a.m. at the 82nd Annual Meeting of the American Meteorological Society in the Orange County Convention Center, Orlando, Fla.
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Contact:
Rob Gutro
Goddard Space Flight Center, Greenbelt, Md.
AMS Press Room: 407/685-5404
E-mail: rgutro@pop900.gsfc.nasa.gov
Cynthia M. O'Carroll
cocarrol@pop100.gsfc.nasa.gov
Goddard Space Flight Center
(Phone:301/614-5563)
Lynn Yarris
Lawrence Berkeley National Laboratory
Phone: 510-486-5375)
E-mail: lcyarris@lbl.gov
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Charting Increased Flow in Six California River Basins - 520 KB TIFF
Recent reports based on climate change scenarios have suggested that California will be subjected to increased wintertime and decreased summertime streamflow.
This figure highlights the probabilities of increased peak daily flow (above average water flow) that are projected to occur in river basins and watersheds as the climate continues to warm on an annual basis.
There were six California basins that were used for the study. The areas stretch from the northern-most area to the east-central region of the state. They areas include: Smith-at Jed Smith, Sacramento at Delta, Feather at Oroville Dam, North Fork American at North Fork Dam, Merced at Pohono Bridge, and Kings at Pine Flat. Each of these basins is represented in this figure by two charts. There are charts for two different climate model inputs (temperature and precipitation), the Hadley Climate Model 2 (HCM) and the National Center for Atmospheric Research Parallel Climate Model (PCM).
The blue circles represent increases that are projected to occur between 2010 and 2039. The triangle represents increases in flow projected between 2040 and 2079. The red circles are projected increases between 2080 and 2100. The upward direction of all of these suggest increased flow and increased flooding potential early in the water year.
California Watersheds Studied for Potential Future Climate Impacts - 264 KB TIFF
Norman Miller and Kathy Bashford of Lawrence Berkeley National Laboratory (LBNL), and Eric Strem of the National Weather Service's (NWS) California-Nevada River Forecast Center
This graphic represents the six California study basins Miller and his colleagues studied to gather historic data, choosing these for their location, elevation and different climatological conditions. The areas stretch from the northern-most area to the east-central region of the state and were chosen for applications to project water demand and ecosystem response.
The areas include: Smith-at Jed Smith, Sacramento at Delta, Feather at Oroville Dam, North Fork American at North Fork Dam, Merced at Pohono Bridge, and Kings at Pine Flat.
Miller said, "The best way to understanding how future climate change will impact water resources is to gather the most data." So the researchers looked at data from these basins from 1963 to 1992 for high flow rates and ranked them. They determined that what used to be considered a high flow from 1960-1990 can now be considered typical.
The Russian River: Scene of an Accurate Flood Prediction in 1995
Pictured here is a dam on the Russian River (Credit: Leslie Hoffman (1997), The Russian River Chamber of Commerce and Visitors Center), and a view from one of the riverbanks (Credit: Mavis Anderson (1997), The Russian River Chamber of Commerce and Visitors Center). The Russian River is located in the northern San Francisco Bay area.
Currently there is a coordinated study underway between LBNL and the NWS to incorporate new remotely sensed satellite data with real-time flood forecasting to reduce the risks associated with floods. Miller and his colleagues used a similar approach to successfully predict the 1995 floods of the Russian River, 48 hours in advance. "By having better data, we'll be able to reduce flooding disasters in the future," Miller said.
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