From: LARRY KLAES (ljk4_at_msn.com)
Date: Thu Mar 06 2003 - 14:17:44 PST
----- Original Message -----
From: Mark Hess
Sent: Thursday, March 06, 2003 3:21 PM
To: News Media list.serv
Subject: CLIMATE CHANGES MAY INCREASE EXTREME RAIN/SNOW EVENTS INCALIFORNIA
Krishna Ramanujan For Release:
Goddard Space Flight Center, Greenbelt, Md. March 6, 2003
(Phone: 301/286-3026)
Kramanuj_at_pop900.gsfc.nasa.gov
Release: 03-25
CLIMATE CHANGES MAY INCREASE EXTREME RAIN/SNOW EVENTS IN CALIFORNIA
Increasing carbon dioxide levels in the atmosphere may lead to a rise
in the number of annual extreme precipitation events in the Sierra
Nevada Mountains, which in turn could increase the frequency of
flooding in California, a NASA-funded study finds.
One of the missions of NASA's Earth Science Enterprise (ESE), which
funded this research, is to better understand how the Earth system is
changing. Within this framework, NASA is committed to studying
variability in global precipitation, how well we can predict future
changes in the Earth system, and what are the consequences of change
in the Earth system for human civilization.
Based on computer model simulations of the next 40 to 50 years,
Jinwon Kim, an atmospheric scientist at the University of California,
Los Angeles (UCLA), found that the Sierra Nevada region may
experience substantial increases in heavy precipitation (exceeding 2
inches of rain/day), and extreme precipitation events (exceeding 4
inches of rain/day). Most of these increases occur during the winter,
currently the wettest season in the region.
"The frequency of extreme precipitation may increase, in general, and
the most notable increase of extreme events may occur in areas
characterized by heavy winter precipitation in today's climate," Kim
said. Kim recently presented his results at the 83rd Annual Meeting
of the American Meteorological Society in Long Beach, Calif.
Existing projections from Hadley Centre for Climate Prediction and
Research (HCCPR) HadCM2 computer model suggests that increases in
carbon dioxide (CO2) are likely to substantially alter the hydrologic
cycle in the Western U.S. That's because increasing levels of CO2 in
the atmosphere trap heat, and warm the air. Warmer air holds more
water, and when parcels of saturated air rise, they tend to rain
water back to Earth.
Kim used his regional computer model (MAS) to make two fine-scale
precipitation projections for the decade of 2040 to 2049 based on
different values of CO2 in the atmosphere from the coarse global
projections by HCCPR, United Kingdom.
Some of the background data input into the computer model included
NASA-derived Normalized Difference Vegetation Index (NDVI) data,
which measures the amount of solar energy reflected and absorbed by
vegetation. This is important data for computing transpiration. NDVI
was created by Compton Tucker of NASA Goddard, using data from the
National Oceanic and Atmospheric Administrationís (NOAA)
Geostationary Environmental Orbiting Satellite (GOES) Advanced Very
High Resolution Radiometer (AVHRR) instrument.
The first projection assumed that greenhouse gas concentrations will
stay at levels equal to those of the late 1900s. The second
projection represented the climate of the same period assuming
increases in greenhouse gas levels by 1 percent per year from the
year 1990.
Compared to the first projection, the second projection showed
increases in both the number of wet days and, more importantly, large
increases in heavy precipitation events for the region during the
cold season from October to March. The model showed increases of
heavy precipitation events increased by 10 to 15 days per year. It
also showed that extreme precipitation events increased by 5 to 10
days per year.
Comparing the two projections, the average number of wet days per
year over the southern and northern Sierra Nevada basins (divided
along the area near Sacramento) increased by 37 percent for the
southern basin and 32 percent for the northern basin in the second
projection. While light precipitation events (less than 5mm or .2
inches/day), stayed the same or decreased slightly for both basins,
the occurrence of heavy precipitation events rose from 1 percent of
wet days annually to 3 percent in the second projection. Extreme
events rose from .1 percent of wet days annually to 1 percent.
Similar changes are projected for all major California basins. These
projections suggest that the intensity of the hydrologic cycle will
increase as levels CO2 continue to climb.
The second model-based projection scenario also showed that elevation
levels in the mountains where freezing occurs will rise as
temperatures rise. That means that much of the precipitation that
currently falls in higher altitudes as snow may come down as rain in
future years. Snow stores water during the cold season and releases
it gradually in spring and summer. Hence, a substantial increase of
cold season rainfall at the expense of snowfall reduces the buffering
effects of snow and could result in more flooding.
These changes, combined with more heavy rain events and steep
mountain slopes, could therefore lead to a greater frequency of
flooding in the future.
"Since the primary concern for reservoir management is to reduce
flooding risks that require maintaining the storage space to capture
excessive runoff, the reservoirs may have to maintain lower water
levels," Kim said. "This directly decreases the water resources."
The climate change signals projected in this study are based on a
single global projection and are expected to include an unknown
amount of uncertainties. Hence, the projections here must be taken as
qualitative, rather than quantitative. The author is planning
additional studies using global projections from multiple Global
Climate Models.
This research was funded by NASA's ESE and NOAA. NASA's ESE
Applications Division applies the results of the nation's investment
in ESE to issues of national concern, such as water and resource
management, environmental quality, community growth, and disaster
management to support policy makers at the state and local levels.
For more information, please see:
http://www.gsfc.nasa.gov/topstory/2003/0210extremeprecip.html
Normalized Difference Vegetation Index (NDVI)
http://daac.gsfc.nasa.gov/CAMPAIGN_DOCS/LAND_BIO/ndvi..html
The Advanced Very High Resolution Radiometer (AVHRR)
http://www.ngdc.noaa.gov/seg/globsys/avhrr.shtml
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