How Dry Can It Possibly Get?
Hilda Blanco
Research Professor
Interim Director, Center for Sustainable Cities
University of Southern California
Urban Water Institute, Annual Conference 8/13/2014
Outline
• Climate change not major driver of SoCal
urban water plans
– Why?
• Climate signal not clear
• Climate change impacts on drought for CA
• IPCC
• NCA
• CA assessment
• Water scarcity and urban water management
in CA
Major Driver of Southland’s Urban
Water Management
• Not climate change
• Imported water
– Reaction to vulnerability of imported water &
increasing prices
• Agencies turning to local water sources
– Groundwater, recycling, stormwater capture, even
desalination
Why is this?
• Cloudy climate signal about the amount of
precipitation
• Why?
– Main effect of warming temperatures:
atmosphere can hold a lot more water
• General effect: more stormy weather
– In CA, it will mean more intense storms
• Reflected in IPCC assessments, not so much in
NCA, and until recently in CA research
Projections about drought
Different scales
Global—IPCC 5th Assessment (2014)
National/Regional—National Climate
Assessment (2014)
State/Regional—California Climate
Assessments (2012)
Major climate impacts on water
resources
IPCC:
Low confidence in increases
in intensity or duration of
droughts
Source: IPCC,AR5, WG1 2014. Summary for Policy Makers, p. 7
“Water resources are already stressed in many parts of North
America due to non-climate change anthropogenic forces, and are
expected to become further stressed due to climate change (high
confidence) [26.3, 26.3.1].
Decreases in snowpacks are already influencing seasonal
streamflows (high confidence) [26.3.1].
While indicative of future conditions, recent floods, droughts, and
changes in mean flow conditions cannot yet be attributed to climate
change (medium to high confidence) [26.3.1, 26.3.2].”
Source: IPCC, AR5, WG2, 2014. Chapter 26 Impacts on North America, p.15
IPCC. Draft 2013. AR5, WG2, Chapter 26, North America Impacts, p. 86.
National Climate
Assessment
(NCA):
For SW, dramatic
reductions in snowpack;
droughts to intensify
NCA: Clear Signal on Water
• Dry areas to get drier,
wet areas, wetter
• Summer droughts to
intensify almost
everywhere due to
longer periods of dry
weather and more
extreme heat
• Longer-term droughts
to intensify in areas of
the Southwest,
southern Great Plains,
and Southeast
• Risks to groundwater
availability and coastal
aquifers
• Flooding may intensify
– Even in regions where total
precipitation projected to decline
• Increasing potential for
flash floods
NCA (2014) Water Supply
http://nca2014.globalchange.gov/highli
ghts/report-findings/water-supply
NCA
Source: NCA. 2014.
Chapter 20. Southwest
Region.
http://nca2014.globalcha
nge.gov/report/regions/s
outhwest
Figure 20.2: Snow water equivalent (SWE) refers to the amount of water held in a volume of snow, which
depends on the density of the snow and other factors. Figure shows projected snow water equivalent for
the Southwest, as a percentage of 1971-2000, assuming continued increases in global emissions (A2
scenario). The size of bars is in proportion to the amount of snow each state contributes to the regional
total; thus, the bars for Arizona are much smaller than those for Colorado, which contributes the most to
region-wide snowpack.
California Assessments
• Clear:
– Decreases in snowpack
– Greater precipitation in form of rain for Northern
California
– Greater likelihood of flooding
• Not clear
– Whether precipitation for Southern California
projected to remain the same, increase or
decrease
California
• “No consistent trend in
the overall amount of
precipitation has been
detected, except that a
larger proportion of
total precipitation is
falling as rain instead of
snow.”
Range of climate model projections
on future precipitation for California
Cayan, D. R., Maurer, E. P., Dettinger, M. D., Tyree, M., &
Hayhoe, K. (2008). Climate change scenarios for the
California region. Climatic Change, 87(Suppl 1), S21-S42.
California Climate Change Center. 2013. Our Changing Climate. A Summary
Report on the Third Assessment from the California Climate Change Center.
http://climatechange.ca.gov/climate_action_team/reports/third_assessment/
Dr. Pierce and colleagues 2013 paper
• Sorted out confused signal
• Figured out:
– Some models projected rare large storms, which
skewed the findings to greater or no change in
total amount of precipitation for California
– Huge storms projected primarily for Sierra Nevada
and Northern California
– When removed, 2X as many projections show
drier conditions
• For Southern California Coast, precipitation 8.4%, and
13.2 in rainy days
Pierce, D.W. et al. 2013. The Key Role of Heavy Precipitation Events in Climate Model Disagreements of
Future Annual Precipitation Changes in California. Journal of Climate, pp. 5879-5896.
The climate picture’s
been cloudy, but it’s
clearing up
Another reason climate change
neglected
Familiarity
Ongoing experience with drought
in Southland
Water Managers and Drought
• Water agencies in region are prepared for
cyclical droughts
– Plans for local water supplies
– BMPs
– Emergency water restrictions
A clearer climate signal calls for action
What kind of action?
The phenomenon may be familiar,
But climate change impacts may not be a
degree change
More of the same may not be adequate
Key Message: Water Resources
Management
In most U.S. regions, water resources
managers and planners will encounter new
risks, vulnerabilities, and opportunities that
may not be properly managed within
existing practices.
NCA (2014) Water Supply
http://nca2014.globalchange.gov/highlights/report-findings/water-supply
LA Times:
Southland falls short of
achieving 20%
voluntary cut in water
use
“Billing problems at the Los Angeles
Department of Water and Power have left the DWP
without a good record of actual water use this year. But
total supply from last July through April — roughly
parallel to demand — rose 3% compared with the same
period in the previous fiscal year.”
Boxall, B. June 21, 2014. Southland falls short of achieving 20% voluntary cut in water us.
Los Angeles Times. http://www.latimes.com/science/la-me-water-use-20140628-story.html
A USC Dornsife/Los Angeles Times poll
in late May found that a majority of
California voters said the drought has
had little or no impact on their daily
lives.”
“
Boxall, B. June 21, 2014. Southland falls short of achieving 20% voluntary cut in water us.
Los Angeles Times. http://www.latimes.com/science/la-me-water-use-20140628-story.html
Conclusion
Cloudy climate signal on precipitation is clearing
up
Drought is likely to intensify, especially in
Southern California
Combined with other climate change impacts
Impacts will challenge urban water managers
especially in SoCal, to develop new
approaches
Thank you!
I’ve been stressing that the message on
drought is clearing up, but Dr. Pierce may tell
you that it’s really getting cloudy, which is
what you really want to hear