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Water and Climate: What's Changing, and Does It Matter to Water Managers?. Dennis P. Lettenmaier Department of Civil and Environmental Engineering University of Washington for 2009 AAAS Annual Meeting Session on 21st Century Water: Friend or Foe? Chicago February 14, 2009.

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Water and climate what s changing and does it matter to water managers
Water and Climate: What's Changing, and Does It Matter to Water Managers?

Dennis P. Lettenmaier

Department of Civil and Environmental Engineering

University of Washington

for

2009 AAAS Annual Meeting

Session on 21st Century Water: Friend or Foe?

Chicago

February 14, 2009


What are the grand challenges in hydrology
What are the “grand challenges” in hydrology? Water Managers?

From Science (2006) 125th Anniversary issue (of eight in Environmental Sciences): Hydrologic forecasting – floods, droughts, and contamination

From the CUAHSI Science and Implementation Plan (2007): … a more comprehensive and … systematic understanding of continental water dynamics …

From the USGCRP Water Cycle Study Group, 2001 (Hornberger Report):[understanding] the causes of water cycle variations on global and regional scales, to what extent [they] are predictable, [and] how … water and nutrient cycles [are] linked?


Important problems all, but I will argue instead (in addition) that understanding hydrologic change should rise to the level of a grand challenge to the community.


From Stewart et al, 2005 addition) that


Magnitude and Consistency of Model-Projected Changes addition) that in Annual Runoff by Water Resources Region, 2041-2060

Median change in annual runoff from 24 numerical experiments (color scale)

and fraction of 24 experiments producing common direction of change (insetnumerical values).

+25%

58%

+10%

67%

Increase

62%

+5%

58%

87%

96%

+2%

62%

62%

71%

87%

-2%

75%

67%

67%

67%

-5%

100%

Decrease

-10%

-25%

(After Milly, P.C.D., K.A. Dunne, A.V. Vecchia, Global pattern of trends in streamflow andwater availability in a changing climate, Nature, 438, 347-350, 2005.)


Timeseries annual average
Timeseries Annual Average addition) that

PCM Projected Colorado R. Temperature

ctrl. avg.

hist. avg.

Period 1 2010-2039 Period 2 2040-2069Period 3 2070-2098


Timeseries annual average1
Timeseries Annual Average addition) that

PCM Projected Colorado R. Precipitation

hist. avg.

ctrl. avg.

Period 1 2010-2039 Period 2 2040-2069Period 3 2070-2098


Annual average hydrograph
Annual Average Hydrograph addition) that

Simulated Historic (1950-1999)Period 1 (2010-2039)Control (static 1995 climate)Period 2 (2040-2069)Period 3 (2070-2098)


Natural flow at lee ferry az
Natural Flow at Lee Ferry, AZ addition) that

allocated20.3 BCM

Currently used 16.3 BCM


Total basin storage
Total Basin Storage addition) that


Annual releases to the lower basin
Annual Releases to the Lower Basin addition) that

target release


Annual releases to mexico
Annual Releases to Mexico addition) that

target release



Case study 1 yakima river basin

Case study 1: Yakima River Basin addition) that

  • Irrigated crops largest agriculture value in the state

  • Precipitation (fall-winter), growing season (spring-summer)

  • Five USBR reservoirs with storage capacity of ~1 million acre-ft, ~30% unregulated annual runoff

  • Snowpack sixth reservoir

  • Water-short years impact water entitlements


Yakima river basin
Yakima River Basin addition) that

2020s

2080s

historical

  • Basin shifts from snow to more rain dominant

    • Water prorating, junior water users receive 75% of allocation

    • Junior irrigators less than 75% prorating (current operations):

      14% historically

      32% in 2020s A1B (15% to 54% range of ensemble members)

      36% in 2040s A1B

      77% in 2080s A1B


Crop Model - Apple Yields addition) that

  • Yields decline from historic by 20% to 25% (2020s) and 40% to 50% (2080s)


PCM addition) that

Business-as-Usual

scenarios

California

(Basin Average)

BAU 3-run average

historical (1950-99)

control (2000-2048)


PCM addition) that

Business-as-Usual Scenarios

Snowpack Changes

California

April 1 SWE


Current climate vs projected climate
Current Climate vs. Projected Climate addition) that

  • Storage Decreases

  • Sacramento

    • Range: 5 - 10 %

    • Mean: 8 %

  • San Joaquin

    • Range: 7 - 14 %

    • Mean: 11 %


Current climate vs projected climate1
Current Climate vs. Projected Climate addition) that

  • Hydropower Losses

  • Central Valley

    • Range: 3 - 18 %

    • Mean: 9 %

  • Sacramento System

    • Range: 3 – 19 %

    • Mean: 9%

  • San Joaquin System

    • Range: 16 – 63 %

    • Mean: 28%


Stationarity—the idea that natural systems fluctuate within an unchanging envelope of variability—is a foundational concept that permeates training and practice in water-resource engineering.

In view of the magnitude and ubiquity of the hydroclimatic change apparently now under way, however, we assert that stationarity is dead and should no longer serve as a central, default assumption in water-resource risk assessment and planning.


How can the water management community respond
How can the water management community respond? within an unchanging envelope of variability—is a foundational concept that permeates training and practice in water-resource engineering.

Central methodological problem: While water managers are used to dealing with risk, they mostly use methods that are heavily linked to the historical record


“Synthetic hydrology” c. 1970 within an unchanging envelope of variability—is a foundational concept that permeates training and practice in water-resource engineering.

Figure adapted from Mandelbrot and Wallis (1969)


Ensembles of Colorado River (Lees Ferry) temperature, precipitation, and discharge for IPCC A2 and B1 scenarios (left), and 50-year segments of tree ring reconstructions of Colorado Discharge (from Woodhouse et al, 2006)


Hybrid Climate Change Perturbations precipitation, and discharge for IPCC A2 and B1 scenarios (left), and 50-year segments of tree ring reconstructions of Colorado Discharge (from Woodhouse et al, 2006)

New time series value = 19000

Objective:

Combine the time series behavior of an observed precipitation, temperature, or streamflow record with changes in probability distributions associated with climate change.

Value from observed time series = 10000


Observed and Climate Change Adjusted Naturalized Streamflow Time Series for the Snake River at Ice Harbor

KAF

KAF

Blue = Observed time series

Red = Climate change time series


Other implications of nonstationarity
Other implications of nonstationarity Time Series for the Snake River at Ice Harbor

  • Hydrologic network design (station discontinuance algorithms won’t work)

  • Need for stability in the evolution of climate scenarios (while recognizing that they will almost certainly change over time)


Another complication water resources research has died in the u s
Another complication: Water resources research has died in the U.S.

  • No federal agency has a competitive research program dedicated to water resources research (e.g., equivalent to the old OWRT)

  • As a result, very few Ph.D. students (and hence young faculty) have entered the area

  • And in turn, the research that would identify alternatives to classic stationarity assumptions is not being done

See Lettenmaier, “Have we dropped the ball on water resources”, ASCE JWRPM editorial, to appear Nov., 2008


Conclusions
Conclusions the U.S.

  • Ample evidence that stationarity assumption is no longer defensible for water planning (especially in the western U.S.)

  • What to replace it with remains an open question

  • A key element though will have to be weaning practitioners from critical period analysis, to risk based approaches (not a new idea!!)

  • Support for the basic research needed to develop alternative methods (a new Harvard Water Program?) is lacking


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