CLIMATE
CHANGE MAY BRING MORE WINTER FLOODS, AND A DRIER GROWING SEASON IN CALIFORNIA
![](images/shim.gif) |
![Map of California's six study basins](https://webarchive.library.unt.edu/eot2008/20090515023412im_/http://www.gsfc.nasa.gov/gsfc/earth/pictures/califclimate/califmapt.gif)
|
| Image
1 | |
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 9º 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 2.7ºF
(or 1.5º Celsius (C)) to 9.0ºF (5.0ºC) and changes in precipitation
from 0.0 to 30.0 percent.
![](images/shim.gif) |
![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.](https://webarchive.library.unt.edu/eot2008/20090515023412im_/http://www.gsfc.nasa.gov/gsfc/earth/pictures/califclimate/fig12topt.gif)
|
![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).](https://webarchive.library.unt.edu/eot2008/20090515023412im_/http://www.gsfc.nasa.gov/gsfc/earth/pictures/califclimate/fig12bottomt.gif) |
Image
2 | Click
on top image and bottom image to enlarge each. | 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. 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. Back
to Top |