Extreme events, water hazards and water supply

Speaker: Marty Ralph (NOAA) Co-authors: Michael Hanemann (UC Berkeley, Arizona State U)

Ben Brooks (U. of Hawaii) Mike Dettinger (USGS and Scripps/UCSD)

Dan Cayan (UCSD/Scripps and USGS)Konstantine Georgakakos (HRC)

Jay Lund (UCD)Jay Famiglietti (UCI)

Michael Anderson (DWR)Jeanine Jones (DWR)

Presented at “Vulnerability and Adaptation to Extreme Events in California in the Context of a Changing Climate: New Scientific Findings”

Scripps Institution of Oceanography, La Jolla, California13 December 2011

Decreasing California Snowpack

Important Energy Facilities in the Delta Would Also Be At Risk

• The Sacramento - San Joaquin Delta is protected by levees.

• Delta islands are below sea level

• Energy Facilities:– Underground natural gas

reservoirs– Transmission lines– Power plants on the west

side of the Delta

Source: PPIC 2007

Sources: CO Climate Report, 2008; Christensen and Lettenmeier, 2007

Projections: Upper Colorado River Basin

2025 2055 2085 2025 2055 2085 2025 2055 2085

• Temperature increases• Precipitation variable• Runoff is earlier in the season and totals decrease by 6–20%

California Water Supply Includes the Colorado River

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Heavy Precipitation and Flooding

Flooding on the Russian River, Guerneville, CA

California averaged $370 M/year in flood damages

3rd highest in the nation

Total Damage in Period 1983-1999(1995 $ equivalent)

LARGEST 3-DAY PRECIPITATION TOTALS, 1950-2008

Ralph, F.M., and Dettinger, M.D., in press, Historical and national perspectives on extreme west-coast precipitation associated with atmospheric rivers during December 2010: Bulletin of the American Meteorological Society, (in press, Nov 2011)

CALIFORNIA’S STORMS ARE AS BIG AS ANY IN THE COUNTRY!

Atmospheric Rivers in IPCC-AR4 climate-change projections by 7 modern GCMs

Dettinger, M.D., 2011, Climate change, atmospheric rivers and floods in California—A multimodel analysis of storm frequency and magnitude changes: Journal of American Water Resources Association, 47, 514-523.

Water Vapor & Low-Level Winds

Obs case

By end of 21st Century, most GCMs yield: •More atmospheric vapor content, but weakening westerlies

Net increase in “intensity” of extreme AR storms

• Warmer ARs (+1.8 C) snowline raised by ~ 1000 feet on average

• Lengthening of AR seasons (maybe?)

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Adaptation

• Central Valley Flood Protection Plan• Scenario development

– Drought Scenario: (Harou etal. 2010, Water Resources Research)

– Storm/flood scenario: “ARkStorm” (Dettinger et al. 2011, Natural Hazards)

• Forecast-Based reservoir Operations (see Willis et al. 2011, San Francisco Estuary and watershed Science)

• Better storm and runoff predictions are a potential adaptive strategy

Central Valley Flood Management Planning Program, 2011, Climate Change Analysis: Attachment 11, 2012 Central Valley Flood Protection Plan, 76 p. (Courtesy of Mike Anderson, CA-DWR)

Central Valley Flood Protection Plan “Thresholds Approach”

Assess Vulnerability & Consequences

Identify Causal Conditions

Assess Likelihoods

Assess Vulnerability & Consequences

Identify Causal Meteorological and Hydrological Conditions

Assess Vulnerability & Consequences

Identify Causal Conditions

Assess Likelihood of Exceedence

Assess Human, Infrastructure and Economic Vulnerabilities

ARkStorm Severe Storm Scenario

Dettinger, M.D., and co-authors, 2011, “Design and quantification of a severe winter storm scenario for emergency preparedness and planning exercises in California.” Natural Hazards, in press, 27 p.

A USGS-led emergency preparedness scenario- Dozens of scientists and

engineers contributed- Shaped by real past

events incl. 1986, 1969, and 1861/62

- Economic impacts estimated to be >$500 B

- Methods and results were peer reviewed

Atmospheric Rivers, Floods and the Water Resources of Californiaby Mike Dettinger, Marty Ralph, , Tapash Das, Paul Neiman, Dan Cayan

Water, 2011 (June)

25-35% of annual precipitation in the

Pacific Northwest fell in association with

atmospheric river events

35-45% of annual precipitation in California

fell in association with atmospheric river events

An average AR transports the

equivalent of 7.5 times the average discharge of the

Mississippi River, or ~10 M acre feet/day

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Conclusions• California has significant vulnerabilities to shifts in extreme

precipitation and runoff• Reduced snow pack is a key risk to water supply, as are

reductions in Colorado River flow and inundation of the Delta

• Changes in the strength of atmospheric rivers and in snow level are key to future flood risks

• Improving monitoring and prediction of critical hydrometeorological conditions can enable adaptation to a changing climate such as by modernizing reservoir operations methods