Dr. Alan F. Hamlet

•JISAO/CSES Climate Impacts Group•Dept. of Civil and Environmental Engineering

University of Washington

21st Century Water Management: The Myth of Climate Stationarity and Strategies for Water Resources Management in a Rapidly Evolving Climate

Climatological Foundation of U.S. Water Resources Planning and Management:

1) Risks are stationary in time.

2) Observed streamflow records are the best estimate of future variability.

3) Systems and operational paradigms that are robust to past variability are robust to future variability.

Observed Streamflows

Planning Models

System Drivers

Schematic of a Typical Water Planning Framework

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Annual streamflow reconstructions at The Dalles, ORusing tree ring growth indices derived from douglas-fir

and limber pine from SE British Columbia - Kamloops to Banff/Jasper (1750-1964)

Columbia Basin Planning Window

Trends in Annual Streamflow at The Dalles from 1858-1998 are strongly downward.

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Relative to the gage record today, flows in the early 20th century appear to be unusually high. How unusual is this period in a longer-term context?

16.4 MAF was considered a conservative estimate at the time of the Compact. However, the average annual flow over the 20th century has been only 15 MAF.

(Figure Courtesy Connie Woodhouse)

“…the timing of the drafting of the Compact was an unfortunate event, in that it did not occur during a representative flow period.”

“The general picture of a collision between water demand and supply in the UCRB in the not-too-distant future is all too apparent.” Stockton and Jacoby 1976

Tree rings placed the gage record in a long-term context

Stockton and Jacoby 1976

Colorado River flow, reconstructed by Stockton and Jacoby, 1976

(Figure Courtesy Connie Woodhouse)

Despite a general awareness of these issues in the water planning community, there is growing evidence that future climate variability will not look like the past and that current planning activities, which frequently use a limited observed streamflow record to represent climate variability, are in danger of repeating the same kind of mistakes made more than 80 years ago in forging the Colorado River Compact.

Long-term planning and specific agreements influenced by this planning (such as long-term water allocation agreements) should be informed by the best and most complete climate information available, but frequently they are not.

What’s the Problem?

Image Credit: National Snow and Ice Data Center, W. O. Field, B. F. Molniahttp://nsidc.org/data/glacier_photo/special_high_res.html

Aug, 13, 1941 Aug, 31, 2004

The Myth of Stationarity Meets the Death of Stationarity

Muir Glacier in Alaska

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Simulated Changes in Natural Runoff Timing in the Naches River Basin Associated with 2 C Warming

Impacts:•Increased winter flow•Earlier and reduced peak flows•Reduced summer flow volume•Reduced late summer low flow

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20th Century Climate “2040s” (+1.7 C) “2060s” (+ 2.25 C)

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Changes in Simulated April 1 Snowpack for the Canadian and U.S. portions of the Columbia River basin(% change relative to current climate)

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Rebalancing Water Systems in Response to Climate Change

Some Conflicting Objectives Likely to be Impacted by Climate Change:

•Hydropower and water supply vs. flood control

•Hydropower and water supply vs. instream flow and ecosystem services.

•Interstate and international transboundary agreements

Flood Control vs. Refill

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Flood Control vs. RefillStreamflow timing shifts can reduce the reliability of reservoir refill

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Flood Control vs. RefillStreamflow timing shifts can reduce the reliability of reservoir refill

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Major U.S. Flood Control Checkpoints

The Dalles

Columbia Falls

Bonners Ferry

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Optimization Reduces Storage Deficits without Jeopardizing Flood Protection

Source: Lee et al. , 2008, Optimized Flood Control in the Columbia River Basin for a Global Warming Scenario, ASCE Journal of Water Resources Planning and Management

20th CenturyCurrent Practice

Adaptation Strategies

Overview of Water Resources Adaptation Challenges:

•Hydroclimatology

•Systems Engineering and Water Resources Engineering Design

•Institutional Considerations

•Politics

•Anticipate changes. Accept that the future climate will be substantially different than the past.

•Use scenario based planning to evaluate options rather than the historic record.

•Expect surprises and plan for flexibility and robustness in the face of uncertain changes rather than counting on one approach.

•Plan for the long haul. Where possible, make adaptive responses and agreements “self tending” to avoid repetitive costs of intervention as impacts increase over time.

Approaches to Adaptation and Planning

Observed Streamflows

Climate Change Scenarios

Planning Models

Altered Streamflows

System Drivers

Schematic of Climate Change Water Planning Framework

•Improved Streamflow Forecasts Incorporating Warming and Other Features of Altered Climate System

•Dynamic Reservoir Operating Systems Using Optimization or Hybrid Optimization/Simulation Approaches to Rebalance the Management System.

Example of a Flexible, Self-Tending Reservoir Operating System

•Such systems are more flexible and adaptable because they do not require a “trigger” for a change in the operating policies, and arguably do not require as much intervention as the climate system gradually changes, because the system responds autonomously to improvements in forecasts (whether related to climate change or other scientific advances)

•These ideas are not really new:

Harvard Water Program ~1965