Part 7:

How the reconstructions are being used in water management

Reconstruction data Policy analysis

Annotated Core Presentation Parts 7-9

Applications of the reconstructions – three main types

1) As qualitative guidance for water managers, stakeholders and decisionmakers

2) For quantitative assessments of long-term hydrologic variability

• For example, assessing the frequency of a recent drought event in the gage record in the context of the longer reconstruction

3) As direct inputs into hydrologic models of a water system

• This allows water managers to model system performance under the tree-ring reconstructed hydrology, as they would do with the gaged hydrology

• Use of the tree-ring data in a water model usually requires further processing of the data (e.g., time-disaggregation)

1) As qualitative guidance for water managers, stakeholders and decisionmakers

Example: Tri-fold brochure developed for Rio Grande Water Conservation District to educate water users about long-term variability in water supply

Example: Analysis of lowest mean reconstructed flows for n-length droughts, Boulder Creek, 1566-2002

Comparison of Lowest Mean Annual Flows for Droughts by Run Length

0

10000

20000

30000

40000

50000

60000

70000

1 2 3 4 5 6

Drought Run Length

Lo

we

st

Me

an

An

nu

al

Flo

w,

Ac

re-F

ee

t

Graphic by Lee Rozaklis, AMEC Earth and Environnmental

2) For quantitative assessments of long-term hydrologic variability

Example: Salt River Project (SRP), AZ. Test of an allotment/pumping strategy

• SRP recognized that the 1950s design drought (6 years) was shorter than the worst expected future droughts

• An 11-year reconstructed drought in the Salt-Verde-Tonto basin (1575-1585) was used to test SRP’s current allotment and pumping strategy

• A simple model, using annual inflows, was used

(3) Input into a system model, to assess management scenarios

Salt River Project: test of allotment/pumping strategy

• The 11-year drought reduced reservoir storage to zero in year 11 (blue)• A slight change in the allotment/pumping scenario increased it above zero (green)

Example: Denver Water: supplemental approach to water supply yield analyses

• Standard approach uses only a 45-year period (1947-1991), and the design drought (1953-1956) probably doesn’t represent a true worst-case scenario

• So this supplemental approach uses two tree-ring flow reconstructions for the main supply basins (common period: 1634-2002)

• However, Denver Water’s system model (PACSM) requires daily model input from 450 locations

• So an “analogue year” approach was used which matches each year in the reconstructed flows with one of the 45 model years (1947-1991) with known hydrology and use that year’s daily hydrology

Denver Water: water supply yield analyses

• Two paleo-droughts (1680s, 1840s) deplete contents lower than 1950s design drought

Reservoir contents with 345 KAF demand and progressive drought restrictions

Example: Bureau of Reclamation: analyses for Colorado River Shortage EIS

Appendix N

Analyses of Hydrologic Variability Sensitivity

“…to evaluate the potential effects to the hydrologic resources of alternative hydrologic inflow sequences.”

Alternative hydrologies:

- Two hydrologies based on tree-ring reconstructions of Lees Ferry flow

- Block resampling of observed flow

- Stochastic manipulation of observed flow

Generate paleo-flow conditionally(K-NN resampling of observed flow)

Nonhomogeneous Markov model with kernel smoothing to generate

system state

Flowchart of paleohydrologic analysesTree-ring reconstruction of annual streamflow at Lees Ferry

Block resample paleo record, retaining paleo flow magnitudes

Convert to binary (wet-dry), calculate transition probabilities

Non-parametric spatial and temporal disaggregation into monthly flows at 29 model nodes

Input into CRSS for policy analyses

“Direct Paleo”“Paleo-Conditioned”

Adapted from Jim Prairie, Reclamation

“Direct Paleo” sequence based on Meko et al. Lees Ferry reconstruction Modeled Lake Powell (orange) and Lake Mead (green) year-end elevationsunder No Action (dashed) and Preferred Alternative (solid)

Model output from Reclamation “Shortage” EIS, 2007

No power from Powell

Who’s using tree-ring reconstructions? (a partial list)

Denver Water Colorado Water Conservation Board Northern Colorado Water Conservancy District Colorado River Water Conservation District Rio Grande Water Conservation District U.S. Bureau of Reclamation – Aspinall UnitCity of Boulder City of Westminster

New Mexico Interstate Stream Commission

Salt River Project (Phoenix) City of Chandler

California Department of Water Resources

Southern Nevada Water Authority

U.S. Bureau of Reclamation - Lower Colorado

Colorado

New Mexico

Arizona

California

Nevada

Multi-state

Responses about use of tree-ring data, from Web survey of tree-ring workshop participants in 2008 (n = 30)

from Rice et al, in review

Part 8:

How the reconstructions are relevant in a changing climate

Calendar Year

1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

An

nu

al

Tem

pe

ratu

re (

F )

41

42

43

44

45

46

47

48

Upper Colorado Basin Mean Annual Temperature.Units: Degrees F. Annual: red. 11-year running mean: blue

Data from PRISM: 1895-2005.

WRCC / CEFA NOAA Westmap

• There is no reason to think that the range of natural hydrologic variability, particularly periods of drought, documented in the past will not be repeated in the future

• The difference will be that events such as drought will likely occur under warmer conditions.

• Although projected changes in precipitation are still uncertain in many area, especially in mountain watershed, projections for temperature are robust.

• Using the reconstructed flows, rather than just the observed record, as the frame of reference for planning can lead to fewer “surprises” as we head into a climatically uncertain future

Even as humans exert a stronger influence on climate, this influence will still be superimposed on natural variability

• One can assume a future warming (e.g, 2 degrees C) and run a hydrologic model to estimate the reduction in flow from that warming, then adjust the reconstructed flows accordingly

• Or, output of projected Temperature and Precipitation from Global Climate Models (GCMs) can be combined with information from flow reconstructions using several different techniques, to generate future-climate-perturbed hydrology

• Either way, the resulting hydrology reflects the joint risk of natural climate variability (as seen in the tree-ring data) and future climate change

Adding warming to the natural flow variability seen in the reconstructions can provide useful scenarios for the future

Example: Integration of tree-ring reconstructed flows with GCM projections - City of Boulder, CO (with Stratus Consulting, University of Colorado, AMEC Earth & Environmental, and NOAA)

• Disaggregated the annual reconstructed streamflows into monthly precipitation and temperature so that those variables could be manipulated independently

• Changes in temperature and precipitation projected from climate models are combined with the tree-ring-derived data to produce simulations of past hydrology under plausible future climate conditions

• Then the simulated monthly temperature and precipitation were input into a snowmelt-runoff (SRM) and water-balance (WATBAL) model to produce modeled Boulder Creek flows

• see Southwest Hydrology, Jan/Feb 2007 for an overview

• Final project report released February 2009

Lee Rozaklis, AMEC Earth and Environmental

Worst case scenario: A “dry” GCM projection imposed on the reconstruction (blue bar = modeled reduction in water delivery)

Example: Integration of tree-ring reconstructed flows with GCM projections – City of Boulder, CO

Combining climate projections with tree-ring reconstructions - other applications and references

• US Bureau of Reclamation: “Long-Term Planning Hydrology based on Various Blends of Instrumental Records, Paleoclimate, and Projected Climate Information”

– Study which evaluated combinations of reconstructions and climate model output for the Gunnison (CO) and Upper Missouri (WY, MT)

– review report released April 2009

• State of Colorado Water Conservation Board – Colorado River Water Availability Study

– Future streamflow scenarois combine paleohydrology with climate projections

• “Climate Change and Water Resources Management: A Federal Perspective” – report by USGS and other agencies (Brekke et al. 2009)

– p. 19: “Paleoclimate information…can be useful for developing climate scenarios that include a wide range of potential hydroclimatic conditions.”

Part 9:

Summary and the TreeFlow web resource

Summary, Part I

1) Tree-ring reconstructions are valuable in that they provide much more “hydrologic experience” than the observed hydrology

2) Tree growth can be particularly sensitive to variations in moisture availability and thus streamflow

3) The methods to develop tree-ring chronologies and streamflow reconstructions are designed to robustly capture and enhance this moisture signal

4) A reconstruction is a best-estimate based on the relationship between tree-growth and gaged flows; there is always uncertainty in the reconstructed flows

Summary, Part II

5) The reconstructions show greater variability than the observed record, including drought events more severe and sustained

6) Reconstructions can be used in a number of different ways to provide guidance to water managers and decision-makers

7) Reconstructions can be combined with projections from climate models to provide plausible scenarios for future hydrology

8) For more information, and easy access to reconstruction data, please visit the TreeFlow web resource:

http://treeflow.info

The TreeFlow web resource - http://treeflow.info

User-friendly, direct, and basin-organized data access for the western US

Data Access PLUS • Instructional materials• Applications information• Workshop archives• Analysis tools