1. California’s Future Climate
Lessons from Scenarios Assessments
Dan Cayan
Scripps Institution of Oceanography, Climate Research Division, UCSD
and
Water Resources Division, USGS
Thanks: Mike Dettinger, Noah Knowles, Mary Tyree
Funding:
PIER Program, California Energy Commission
RISA Program, NOAA Office of Global Programs
DOE
More info:
http//:meteora.ucsd.edu/CAP/

2. California Climate Change Scenarios Assessment some lessons learned
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

3. Vulnerability: response to a +3ºC warming
What fraction of each year’s precipitation historically fell on days with average temperatures just below freezing?
YOSEMITE
Less vulnerable
More vulnerable
“Rain vs Snow”
Computed by Mike Dettinger from gridded historical US weather data (from Bates et al, in rev)

4. More Rain
Less Snow WY
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 lower trend significance (p>0.05).
Noah Knowles et al. 2006
in press J. Climate

5. 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

6. since 1985 the number of large wildfires in western U. S
since 1985 the number of large wildfires in western U.S. increased by 4X
Anthony Westerling et al. Science August 2006

7. Large wildfire threat is aggravated by warmer springs and summers
Anthony Westerling et al. Science August 2006

8. Ocean Beach , February 1983
Extreme storm-forced sea levels during an extreme tide

9. Observed SFO (left) and modeled Global (right)
Observed SFO (left) and modeled Global (right). Sea level rise estimates based upon an envelope of output from several GHG emission scenarios
Projected envelope of global s.l. rise
observed
Climate models
Only provide loose guidance on
The amount of sea level rise, but
It is very likely that rates will increase

10. San Francisco Bay/Delta Water Levels
Confluence of sea level rise and increased flooding
~Jan
Nasa
/ncalifflood_amo_ _lrg.jpg

11. Uncertainty: Projected Warming Ranges Statewide annual average (°F)
14.4
10.8 9
3.6
-3.6
Higher Warming Range
Medium Warming Range
Temperature Change (°F)
Lower
Warming Range

12. Meditterranean precipitation regime remains

13. 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,
IPCC SRES runs
Mike Dettinger, 2005
San Fran. Estuary and Watershed Science

14. Projected patterns of precipitation changes
versus
Globally, dry regions become drier?

15. Challenges Mike Dettinger, Jim Wells USGS and SIO
record streamflow in Tuolumne Meadows

16. Seasonally intensified warming?
some models suggest amplified summer warming

17. GFDL CM2.1 Jun-Aug air temp change
Climate models project
1.5-2.C ocean surface warming by end–of-century.
Greater warming on land than oceans would amplify California coast-interior thermal gradient.
Summer land warming
is accentuated
GFDL CM2.1 Jun-Aug air temp change
minus
GFDL CM2.1 is a medium-high sensitivity model. Other models produce less (or more) warming

18. Modeling climate over California’s complex terrain: July 10m Wind Diurnal Variation

19. Are models capable of producing realistic suite of wet and dry spells?
Distribution of
Obs and simulated
5yr precip departures
obs
Sacramento drainage div
sim
sim
Hist means (inches):
Div
Gfdl 43.13
Pcm 29.63

20. California needs a sustained modern Climate Observation Network
Douglas Alden
Scripps Institution
of Oceanography
Installing met station
Lee Vining, CA

21. Implications for Monitoring
Primary snowpack loss is above ~1500m
This is to show what elevs we should be monitoring. I chose >1500m as a threshold for the next slide.
Knowles and Cayan, 2004

22. Rain-snow transition zone Needs more Careful monitoing
Over all Stream gages, present-day elevational bias is small…
Total number of stream gages below 1500m (red)
Total number of gages above 1500m (blue)
…but climate-quality HCDN subset is under-represented in crucial elevations.
Top: all gages, bottom: hcdn only
Red: above 1500m (~snowline), blue: below (see left and right y-axes)
Key to this slide is that CA has ~5x as much area below 1500m as above. Y-axes are scaled accordingly, so that red and blue lines coincide if no gage elev bias (rel to 1500m threshold anyway).
Take-home is that for all gages, avg gage dens above 1500m is ~same as below BUT
HCDN avg gage dens above 1500m is ~half what it is below 1500m.
Total number of HCDN gages below 1500m (red)
Total number of HCDN gages above 1500m (blue)
Noah Knowles, USGS)

23. …on the other hand, it can be very wet
May 16th A warm storm in the Sierra
Yosemite Valley floods from a 1” rain

24. GHG Emissions Scenario
need to understand event scale phenomena
projected heat wave days
SRES A2
GHG Emissions Scenario

25. Need observations of 3-d, upstream atmosphere
Slide 11
Slide 11
Hydromet testbed, NOAA ETL and collaborators

26. How to effectively work and learn across disciplines?
Impacts
Physical
Ecological
Economic
Social
Scenarios, not forecasts
PCM. GFDL, HAD
Model-based
Climate Projections
Human
Health
Forests/
Fire
Agriculture
Coasts
Water
Energy
Coping Capacity/Preparedness
Susi Moser, NCAR

27. Recommendations (without much discussion) :
Improved, sustained observations
higher spatial resolution, more coverage
3-d atmosphere and ocean upstream
California meso-micro climates including urban and agricultural settings
improve insitu network, real-time communications
scientific quality record keeping of economic, social measures
data archeology
Continued modeling at several scales, disciplines
Ongoing climate simulation compute consortium Ongoing Consortium for
climate simulation/prediction to knit state/campuses/labs
End-to-end assessments, including eco, economic, social; close State participation
Study extreme events as well as secular changes
Study aerosol-clouds-precipitation
Link with other regional, national, international efforts
Support California State Climate Scenarios Assessments
Promote CEC-PIER Annual Climate Change Conference
Develop closer, better links to decision makers; strengthen outreach
Fellowship program for grad students, post docs to ensure continuity, new generation