cayan_snc.pdf
Western Judges SIO 11/12/2007
Climate Change
Sierra Nevada Conservancy 12/5//2007
a challenge looming for the Sierra Nevada
Climate Change
Dan Cayan
a challenge looming for the Sierra Nevada
Scripps Inst
Dan Ca
it
yanution of Oceanography, Climate Research Division
and US Geological Survey
Scripps Institution of Oceanography, Climate Research Division
and US Geological Survey
in collaboration with:
in collaboration with:
Mike Dettinger
Noah Knowles
Mike Dettinger
Tony Westerling
Noah Knowles
Mary Tyree
Tony Westerling
Mary Tyree
Connie Millar
sponsors:
Kelly Redmond
NOAA OGP RISA element
California Energy Commission PIER program
sponsors:
NOAA OGP RISA element
http://meteora.ucsd.edu/cap
California Energy Commission PIER program
http://meteora.ucsd.edu/cap
What are Observations
telling us?
Symptoms of a warmer climate?
Mike Dettinger, Jim Wells USGS and SIO
record streamflow in Tuolumne Meadows
A Rapidly Warming World
1.1 °F
Moberg et al. Nature 2005
North America Eurasia
Strong warming of
No. Hemisphere
especially during
winter and spring
1950-2000 37.5N-80N
Very broad spring warming 1950-1997
During
recent
history,
temperature
changes in
west U.S.
have
tracked
those in
global
temperature
Dry & Wet
days have
warmed
1950-2000
less snow, more rain
earlier snowmelt
Warming in the free atmosphere has been accentuated aloft
Reanalysis Cross Sections
34-38 N from 90 to 130 W
Potential Temperature Trend
Jan-Dec
1948-2001
Kelly Redmond
Sierra Annual Jan-Dec 700 mb Temp (10,000 ft)
1 C
Kelly Redmond
How much snowpack
will be lost?
Douglas Alden
Scripps Institution
of Oceanography
Installing met station
Lee Vining, CA
Western
Spring
Snowpack
has declined
since 1950
Trends in April 1
Snow Water
Equivalent 1950-
1997
Source: Phil Mote et al. (2004) (university of Washington
SENSITIVITY TO A +3ºC WARMING…
What fraction
of each year’s
precipitation
historically fell
on days with
average
temperatures
just below
YOSEMITE
freezing?
Less vulnerable
More vulnerable
“Rain vs Snow”
Computed by Mike Dettinger from gridded
historical US weather data (from Bates et al, in
rev)
More Rain
Less Snow
WY 1949-2004
Winter (Nov-Mar) SFE/P trends at western US
weather stations: symbol area is proportional to
study-period changes, measured in standard
deviations as indicated; circles indicate high
trend significance (p<0.05), squares indicate
Noah Knowles et al. 2006
lower trend significance (p>0.05).
in press J. Climate
…on the other hand, it can be very wet
May 16th 2005 A warm storm in the Sierra
Yosemite Valley floods from a 1” rain
As a result of streamflow timing trends, the
warm-season fraction of annual streamflow has declined.
Sum of natural flows from 8 major rivers in the Sierra Nevada
Roos, 1989, 1991; Dettinger and
Cayan, 1995
By several measures,
Western snowfed
streamflow has been
arriving earlier in the
Spring-pulse dates
year in recent
decades
Center
time
Spring
pulse
Centers of Mass
Stewart et al., 2004; Stewart et al., 2005 J. Clim.
Plant bloom timing
advanced by 1 wk
at cooperative
observer sites in the
western United States
1957-1994
Cayan et al., 2001; Bull Am Met Soc
Mar-Apr 2004
record
warmth and
early runoff
Pagano et al EOS Oct 2004
During late 1970’s - early 1990’s
Limber Pine has had burst of
recruitment, in particular at higher
elevations than previous treeline
Connie Millar, Bob Westfall
since 1985 the number of large wildfires in western U.S. increased by 4X
Anthony Westerling et al. Science August 2006
Large
wildfire
threat is
aggravated
by warmer
springs and
summers
Anthony Westerling et al. Science August 2006
Springs with earlier snowmelt have produced
summers with higher wildfire
Anthony Westerling et al. Science August 2006
What are
recent
climate
model
simulations
telling us?
Variations of the Earth’s surface temperature
Departures in temperature in oC (from the 1990 value)
8
Projections
6
4
2
Proxy
Instrument
0
oF
oC
Projected Warming Ranges
Statewide annual average (°F)
8
14.4
e
)
F
6
10.8
o ng
Higher Warming
ha
Range
e C
9 4
Medium
t
ur
a
Warming Range
3.62
per
Lower
Warming Range
em
T
0
0
Temperature Change (°F)
-3.6
- 2
1 9 7 5
2 0 0 0
2 0 2 5
2 0 5 0
2 0 7 5
2 1 0 0
A 1 H a d C M 3
A 1 P C M
A 2 H a d C M 3
A 2 G F D L 2 .1
A 2 P C M
B 1 H a d C M 3
B 1 G F D L 2 .1
B 1 P C M
Climate models project
GFDL CM2.1 Jun-Aug air temp change
ocean warming by end of
2070-2099 minus 1961-1990
century of 1.5-2.C
greater warming on land
than oceans would amplify
thermal gradient across
California coast-interior
Summer land warming
is accentuated
need to understand event scale phenomena
projected heat wave days
SRES A2
GHG Emissions Scenario
California can be
a very dry place!
SIO installs weather
Monitoring transect
West Piute Ridge
White Mountains
northeast of Bishop
historically:
“Cool” storms
contribute
immediate runoff
from smaller areas
of the river basin
runo
ff
(the rest goes into
snowpack for later)
In a warmer climate:
Warm storms
contribute
immediate runoff
from larger areas
runo
of the river basin
ff
We face significant losses of spring snowpack
• Less snow,
more rain
• Particularly at
lower elevations
• Earlier run-off
• More floods
• Less stored
water
By the end of the century California could lose half of its late spring
snow pack due to climate warming. This simulation by Noah
Knowles is guided by temperature changes from PCM’s Business-as-
usual climate simulation. (a middle of the road emissions scenario)
Knowles and Cayan 2001
Global Precipitation—
SoCal is under the effect of one of the subtropical dry zones
Sierra Nevada
Winter-Centered
12-Month
July - June
Precipitation
Thru June 2007
…..and more volatile than other
western basins
Columbia
Sierra drainage (140,000km2 is only
about 1/4 of the area of the
Columbia or the Colorado.
Sierra drainage generates 31.8km3 runoff
, ~1/5 of that in the Columbia
but ~2x of that in the Colorado.
Reservoir storage in California is about
49 km3. This is the equivalent of about
1yr supply of State’s developed runoff.
Sierra 8 Rivers
Storage on the Columbia (60km3) and
Colorado (74km3) is larger, but still is
impacted by climate variability.
The relative variability of the Sierra stream discharge is the largest of the three
major watersheds in the western United States. Compared to Columbia Basin whose
coefficient of variation (std dev/mean) is 0.19, the Sierra combined basins Vary
greatly, with c.v. of 0.44. The Sierra annual discharge has varied from twice to half
of historical average
multi-year dry spells
Evidence for deep droughts
during medieval period
Connie Millar
Although models unanimously indicate a warmer
climate, they are undecided if it will get wetter or dry out
6 different climate models
5 emission scenarios,
Mike Dettinger, 2005
IPCC SRES runs
San Fran. Estuary and Watershed Science
Projected patterns of precipitation changes
2090-2099 versus 1980-1999
Globally, dry regions become drier?
Gov Swartzenegger’s
June 2005 Executive Order
commissioned this
Climate Assessment, which
investigated potential climate
change impacts and formed key
scientific background for
California’s greenhouse gas
emissions legislation, AB-32
which was passed in fall 2006
Available on the web at
http://www.climatechange.ca.gov/b
iennial_reports/2006report/
Summing up:
OBSERVATIONS AND MODELS INDICATE:
The West has a dry, volatile climate. Our water supply is vulnerable to
climate changes and weather extremes.
Humans have altered atmospheric composition and thus are altering the
earth’s climate; GH gases have long lifetimes, so choices made now and
in future will greatly impact future climate.
Warming is already underway and more to come +2 to +5 ºF by 2050
Recent model projections suggest warming may be intensified
in summer, especially in interior areas.
Recent IPCC model projections for western precipitation are scattered,
but several show moderate drying as tends to be characteristic
of Mediterranean regions globally.
Warmer winter storms would produce more rain, less snow, earlier flows,
more floods. “Shoulders” of watersheds at 6000-8000’ would generate
more immediate runoff.
Frank Gehrke,
California Cooperative Snow Surveys, DWR
OBSERVATIONS AND MODELS INDICATE:
Western Ecosystems are vulnerable to climate change--
snow hydro-climate changes across elevational gradients,
heightened wildfire risks.
Models predict greater warming in summer than in winter and
higher rates of warming at increased elevations.
In the future, floods may be intensified as larger proportions
of mountain catchments are likely to produce rainfall runoff
instead of snowpack
Reduced spring snowpack is likely, and in proportion to climate warming
Climate monitoring is imperative to track changes in the midst of
variability and to inform better decisions
