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How the reconstructions are being used in water management

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1 How the reconstructions are being used in water management
Annotated Core Presentation Parts 7-9 Part 7: How the reconstructions are being used in water management In Part 7, we describe first generally, and then with specific examples of applications from the western US, how tree-ring reconstructions can be used in water resource planning and management. Reconstruction data Policy analysis

2 Applications of the reconstructions – three main types
As qualitative guidance for water managers, stakeholders and decisionmakers 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 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) The potential applications of the reconstructions covers a broad spectrum, depending on the information needs, institutional context, and technical capacity of the entity using the data. Here we list three broad categories of applications, from less to more quantitatively involved.

3 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 Here is an example of how a water district in Colorado used a brochure combining text and graphics to convey to their stakeholders (mainly agricultural irrigators) the lessons of the reconstructions about hydrologic variability.

4 Graphic by Lee Rozaklis, AMEC Earth and Environnmental
2) For quantitative assessments of long-term hydrologic variability Example: Analysis of lowest mean reconstructed flows for n-length droughts, Boulder Creek, And here is an example of a relatively simple analysis performed by a consultant for the City of Boulder, CO, to extract the most severe droughts of varying lengths (1-6 years) from a streamflow reconstruction. The height of each bar shows the mean annual flow for the n-year period with the lowest mean annual flow of all n-year periods in the reconstruction. This drought-severity “profile” could then be compared to the same metrics extracted from the observed flow record. Graphic by Lee Rozaklis, AMEC Earth and Environnmental

5 (3) Input into a system model, to assess management scenarios
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 ( ) was used to test SRP’s current allotment and pumping strategy A simple model, using annual inflows, was used And we have three examples of the use of tree-ring reconstructions in models to explore different management scenarios. The first example, from the Salt River Project, uses a very simple model (which runs on an Excel spreadsheet) to test the system outputs under a reconstructed severe and sustained drought, and different strategies for allotment and pumping.

6 Salt River Project: test of allotment/pumping strategy
With the current strategy (blue trace), the system runs out of reservoir storage by the end of the drought. Changing the strategy slightly (green trace) leads to positive storage at the end of the 11-year drought, and the SRP manager who ran the model “gets to keep his job for another year”, as he put it. In this case, the change in strategy involved changing the threshold for using more groundwater, to conserve surface water supply. 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)

7 Example: Denver Water: supplemental approach to water supply yield analyses
Standard approach uses only a 45-year period ( ), and the design drought ( ) 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: ) 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 ( ) with known hydrology and use that year’s daily hydrology Our second example, from Denver Water, also was motivated by the realization that the design drought (“critical period”) derived from the observed record may not represent a sufficient test of their robustness of water supply to future droughts. Because the model used here was a full water system model requiring daily inputs at hundreds of nodes, the two annual flow reconstructions needed to be disaggregated in space and time before being input into the model. The Denver Water engineers arrived at an analogue approach in which the daily observed values at all nodes for a given year from were substituted for the “paleo-year” ( ) for which the reconstructed annual flow was most similar to that year’s observed annual flow.

8 Denver Water: water supply yield analyses
Reservoir contents with 345 KAF demand and progressive drought restrictions What Denver Water found, when they ran the model input for derived from the reconstructions, was that there were two droughts prior to the observed period (in the 1680s and 1840s) which depleted reservoir contents more than the existing design drought. But even in the 1840’s drought their reservoirs were not quite depleted to their strategic water reserve, which indicated that under the assumed demand (345 KAF) and applying progressive drought restrictions on use, Denver Water’s system was robust to the worst reconstructed drought. Two paleo-droughts (1680s, 1840s) deplete contents lower than 1950s design drought

9 Analyses of Hydrologic Variability Sensitivity
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 The final example of using tree-ring data for system modeling is the analyses done by the US Bureau of Reclamation for the Final EIS, “Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead”, released in November In Appendix N, “Analyses of Hydrologic Variability Sensitivity”, four different types of hydrologies were generated to test sensitivity to policy alternatives, including two hydrologies based on the Meko et al. (2007) reconstruction of Lees Ferry streamflow. Reference: See Appendix N, Analysis of Hydrologic Variability Sensitivity for more details

10 Flowchart of paleohydrologic analyses
Tree-ring reconstruction of annual streamflow at Lees Ferry “Paleo-Conditioned” “Direct Paleo” Convert to binary (wet-dry), calculate transition probabilities Block resample paleo record, retaining paleo flow magnitudes Nonhomogeneous Markov model with kernel smoothing to generate system state Generate paleo-flow conditionally (K-NN resampling of observed flow) The steps used to generate the two types of hydrology (60-year flow sequences) based on tree-ring data are shown here. On the left is the “Paleo-conditioned” method, which uses the system state (wet-dry) information (e.g., maximum drought length) to generate sequences that are representative of the tree-ring reconstruction, but resamples the observed flow record to obtain the flow values for each year. The “Direct Paleo” method simply resamples blocks of the reconstructed flows to generate flow sequences. The resampling method is described in Prairie et al In both cases, the generated annual flow values for Lees Ferry are spatially and temporally disaggregated to the monthly flows at 29 nodes needed for input into the CRSS model. This non-parametric disaggregation method is described in Prairie et al References: Prairie, J., Nowak, K. Rajagopalan,  B., Lall, U. and Fulp, T., (2008) A stochastic nonparametric approach for streamflow generation combining observational and paleo reconstructed data. Water Resources Research, 44, W06423 Prairie, J., Rajagopalan,  B., Lall, U. and Fulp, T., (2007) A stochastic nonparametric technique for space-time disaggregation of streamflows. Water Resources Research, 43, W03432 Non-parametric spatial and temporal disaggregation into monthly flows at 29 model nodes Input into CRSS for policy analyses Adapted from Jim Prairie, Reclamation

11 Model output from Reclamation “Shortage” EIS, 2007
“Direct Paleo” sequence based on Meko et al. Lees Ferry reconstruction Modeled Lake Powell (orange) and Lake Mead (green) year-end elevations under No Action (dashed) and Preferred Alternative (solid) Here is a graph of CRSS model output that appeared in the Final EIS. The hydrologic input to the model is a “direct paleo” sequence—the years from the Meko et al. (2007) reconstruction of Lees Ferry. So, in effect, this graph shows what would have happened if the current Colorado River infrastructure and policies (given the modeling assumptions) had been subjected to the mid-1100s drought recorded by the tree rings. The orange lines show the modeled level of Lake Powell over a ~60 year period under two policy alternatives. In both scenarios, the reservoir drops below the level needed to generate hydropower in ~2025 and stays below that level for a total of ~25 years. This depletion of Powell is required to keep the level of downstream Lake Mead (green lines) steady and above the level of the water intakes for the Southern Nevada Water Authority (Las Vegas). No power from Powell

12 Who’s using tree-ring reconstructions? (a partial list)
Colorado New Mexico Arizona California Nevada Multi-state 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 Unit City 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 Here are selected water entities using the tree-ring reconstructions in communications, analyses, and modeling. The large number of Colorado users reflects the greater number of reconstructions available for Colorado watersheds than in other states—a disparity that will hopefully shrink in the future as the development and use of the reconstructions becomes more widespread.

13 from Rice et al, in review
Responses about use of tree-ring data, from Web survey of tree-ring workshop participants in 2008 (n = 30) This graphic shows the responses of 30 tree-ring workshop participants (mainly water managers) about how they and their organizations have actually used tree-ring reconstructions (Rice et al., in press). Note that while only a relatively small number noted their use of tree-ring reconstructions in quantitative analyses and modeling, a majority responded that the reconstructions have broadened understanding of hydrologic variability, and informed planning and decision-making. In other words, the reconstructions doesn’t have to subjected to further analysis or run through models in order to provide valuable information. That said, for some organizations, explicit modeling may be required to produce information about risk that is comparable with other (non-tree-ring) data, and also has credibility with decision-makers in that organization. Reference: Rice, J. L., Woodhouse, C. A., and Lukas, J. J. In press. Science and decision-making: Water management and tree-ring data in the western United States. Journal of the American Water Resources Association. See also links to the study report at the bottom of the About TreeFlow page (http://treeflow.info/about.html) from Rice et al, in review

14 How the reconstructions are relevant in a changing climate
Part 8: How the reconstructions are relevant in a changing climate Up to this point, we have not directly addressed an important question: If the climate is changing, and future climate and hydrology is going to be different than in the past, of what relevance is information about the past (e.g., tree-ring reconstructions of streamflow)? In Part 8, we argue for the continued relevance of robust information about past climate and hydrology.

15 Even as humans exert a stronger influence on climate, this influence will still be superimposed on natural variability 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 The short answer is that the past (natural climate variability) is not going to go away. Future hydrologic variability will likely be a function of natural hydrologic variability (driven largely by variations in precipitation), plus the effects of the significant anthropogenic warming that is occurring and will continue, plus any future anthropogenic changes in precipitation--which are as yet very uncertain, especially in mountain regions of the western US.

16 Adding warming to the natural flow variability seen in the reconstructions can provide useful scenarios for the future 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 While the tree-ring reconstructions are useful by themselves, as a better representation of more challenging future conditions than the observed record, they can also be combined with information about projected climate change—either a specific scenario, or a set of scenarios generated from GCMs.

17 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 Described here is one of the first efforts to combine the reconstructed flows with GCM output, and use the joint information in a water system model (for the City of Boulder) to assess the robustness of water policies under plausible future conditions. A full description of this project can be found in the project report:

18 Example: Integration of tree-ring reconstructed flows with GCM projections – City of Boulder, CO
Worst case scenario: A “dry” GCM projection imposed on the reconstruction (blue bar = modeled reduction in water delivery) Output from 3 different GCMs was used for this study, and an ensemble of flow sequences were generated from each set of GCM output. Here is shown a true “worst-case scenario”, in which a “dry” GCM projection was combined with the reconstructed flows, to simulate the paleo period ( ) under conditions of climate change. The height of the blue bars shows the extent of modeled water shortage in each year. The years from contain many shortages, but very few during the most recent century (period of record). This shows how looking just at the period of record wouldn’t indicate the vulnerability of the city’s water system nearly as well; the combination of “paleo” and “future” is a harsher test of the system. Lee Rozaklis, AMEC Earth and Environmental

19 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.” As water agencies are starting to more directly grapple with climate change in assessing vulnerability and risk, more of them are looking at using the past (tree-ring reconstructions) in combination with future climate projections. We recognize that most entities do not have the resources of Reclamation, the state of Colorado, or even the City of Boulder, to explicitly model the impacts of paleohydrology + climate change. But just the concept of combining them is potentially useful in that it makes us more aware that the hydrology of the future will combine past variability and future climate trends. References: Colorado River Water Availability Study web page at Colorado Water Conservation Board: - Draft report available as of June 2010 on CWCB homepage (http://cwcb.state.co.us) Brekke, L.D., Kiang, J.E., Olsen, J.R., Pulwarty, R.S., Raff, D.A., Turnipseed, D.P., Webb, R.S., and White, K.D., 2009, Climate change and water resources management—A federal perspective: U.S. Geological Survey Circular 1331, 65 p. (Also available online at

20 Summary and the TreeFlow web resource
Part 9: Summary and the TreeFlow web resource Finally, Part 9 provides a brief summary of the presentation and introduces the TreeFlow web resource (for those viewers who did not go through TreeFlow to access the presentation).

21 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 I

22 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: Summary, Part II

23 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 TreeFlow is a comprehensive web resource on tree-ring reconstructions of streamflow and climate for the western US, providing access to reconstruction data as well as information on data development and applications. While the primary users of streamflow reconstructions are water resource professionals, people in many other sectors and disciplines may find the data useful. TreeFlow is intended to be a dynamic resource. We have designed the pages to be expanded as reconstructions are generated for other basins, and as new applications are developed. We welcome the contributions of other researchers and water providers. In the future, we also will include other hydrologic reconstruction resources, such as a network of Rocky Mountain snowpack reconstructions and North American monsoon reconstructions that are currently under development. TreeFlow is a collaborative effort of researchers affiliated with three NOAA-funded Regional Integrated Sciences and Assessments (RISA) programs: Climate Assessment for the Southwest (CLIMAS) Western Water Assessment, and the Climate Impacts Group. The TreeFlow website is housed on a server at Institute for Environment and Society (home of CLIMAS) at the University of Arizona. If you have any questions or comments about this presentation, or the TreeFlow web resource, please contact Connie Woodhouse


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