How Dry Can It Possibly Get?Hilda Blanco

Research ProfessorInterim Director, Center for Sustainable Cities

University of Southern CaliforniaUrban 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 scalesGlobal—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

“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 While indicative of future conditions, recent floods, droughts, and changes in mean flow conditions cannot yet be attributed to climate changes in mean flow conditions cannot yet be attributed to climate change (medium to high confidencechange (medium to high confidence) [26.3.1, 26.3.2].”

Source: IPCC,AR5, WG1 2014. Summary for Policy Makers, p. 7

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/highlights/report-findings/water-supply

NCA

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.

Source: NCA. 2014. Chapter 20. Southwest Region. http://nca2014.globalchange.gov/report/regions/southwest

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.”

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/

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.

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 actionWhat 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 ManagementIn 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 CaliforniaCombined 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