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Water and Climate: What's Changing, and Does It Matter to Water Managers?

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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 – PowerPoint PPT presentation

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Title: Water and Climate: What's Changing, and Does It Matter to Water Managers?


1
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

2
What are the grand challenges in hydrology?
  • 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?

3
  • 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.

4
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5
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6
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7
From Stewart et al, 2005
8
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9
Timeseries Annual
Average
PCM Projected Colorado R. Temperature
ctrl. avg.
hist. avg.
Period 1 2010-2039 Period 2 2040-2069
Period 3 2070-2098
10
Timeseries Annual
Average
PCM Projected Colorado R. Precipitation
hist. avg.
ctrl. avg.
Period 1 2010-2039 Period 2 2040-2069
Period 3 2070-2098
11
Annual Average Hydrograph
Simulated Historic (1950-1999) Period 1
(2010-2039)Control (static 1995 climate) Period
2 (2040-2069) Period 3 (2070-2098)
12
Natural Flow at Lee Ferry, AZ
allocated20.3 BCM
Currently used 16.3 BCM
13
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14
Total Basin Storage
15
Annual Releases to the Lower Basin
target release
16
Annual Releases to Mexico
target release
17
Annual Hydropower Production
18
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19
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20
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21
Case study 1 Yakima River Basin
  • 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

22
Yakima River Basin
  • 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

23
Crop Model - Apple Yields
  • Yields decline from historic by 20 to 25
    (2020s) and 40 to 50 (2080s)

24
PCM Business-as-Usual scenarios California
(Basin Average)
BAU 3-run average
historical (1950-99)
control (2000-2048)
25
PCM Business-as-Usual Scenarios Snowpack
Changes California April 1 SWE
26
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27
Current Climate vs. Projected Climate
  • Storage Decreases
  • Sacramento
  • Range 5 - 10
  • Mean 8
  • San Joaquin
  • Range 7 - 14
  • Mean 11

28
Current Climate vs. Projected Climate
  • Hydropower Losses
  • Central Valley
  • Range 3 - 18
  • Mean 9
  • Sacramento System
  • Range 3 19
  • Mean 9
  • San Joaquin System
  • Range 16 63
  • Mean 28

29
Stationaritythe idea that natural systems
fluctuate within an unchanging envelope of
variabilityis 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.
30
How can the water management community respond?
Central methodological problem While water
managers are used to dealing with risk, they
mostly use methods that are heavily linked to the
historical record
31
Synthetic hydrology c. 1970
Figure adapted from Mandelbrot and Wallis (1969)
32
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)
33
Hybrid Climate Change Perturbations
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
34
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
35
Other implications of nonstationarity
  • Hydrologic network design (station discontinuance
    algorithms wont work)
  • Need for stability in the evolution of climate
    scenarios (while recognizing that they will
    almost certainly change over time)

36
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
37
Conclusions
  • 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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