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Ongoing CRB R2O Research
Recently Completed CRB R2O Research (post-2016)
2008 – 2016 Research
Publication Abstracts

In 2004, Reclamation’s Lower Colorado Region (LC Region) initiated a research and development program to investigate new methods of projecting future Colorado River flows that could incorporate increased hydrologic variability and the potential for decreased annual flow due to a changing climate. The program (called the “Colorado River Hydrology Workgroup” until 2018 when the name was changed to the “CRB R2O Program”) sought to collaborate with other federal agencies and universities in conducting research to gain knowledge and understanding of the potential impacts of climate change and climate variability on the Colorado River.

As part of this effort and in conjunction with the development of the Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead Final Environmental Impact Statement (EIS), Reclamation enlisted a group of leading climate experts to assess the state of climatic and hydrologic knowledge in the Colorado River Basin and to help prioritize future research and development needs. Their findings and recommendations were summarized in a final report which was published as Appendix U to the EIS.

The report produced nine recommendations that have informed the activities of the research and development program:

1. Improve availability and temporal resolution of regional climate projection datasets
2. Improve ability to model runoff under climate change
3. Investigate paradigm for Colorado River Basin precipitation response
4. Diagnose and improve existing climate models before adding additional features
5. Investigate changes in modeled climate variability at multiple time scales
6. Improve understanding of surface water, groundwater and land cover interaction
7. Improve prediction of interdecadal oscillations
8. Investigate use of paleo record to inform modeled streamflow variability
9. Interact with Federal Climate Change Science Program and other climate change research initiatives

Though the Colorado River Hydrology Workgroup originated in the LC Region, the Upper Colorado Region also contributed direction, expertise, and funding.

Studies completed between 2008 and 2016 are listed in the table below with links to brief summaries. The studies are organized by institution and year of initiation.

Upper Colorado River Basin Streamflow Reconstructions

Institution: University of Arizona

Years: 2007 – 2008

PI(s): Meko

Project scientist(s): Woodhouse, Knight, Lukas, Hughes, Salzer

Summary: Cores from living trees and cross-sections from remnant wood were collected between 2002 and 2005 at 11 sites in the Upper Colorado River Basin to reconstruct annual water year flows from year 762 to 2005 on the Colorado River at Lees Ferry. This sequence is of particular interest because it extends into the Medieval Climate Anomaly, a period of time (900 to 1300) when various paleoclimate data indicate hydrologic droughts in the western United States were abnormally widespread.

Product(s):

Final Environmental Impact Statement on the Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead, Appendix N: Analysis of Hydrologic Variability Sensitivity

Meko, D.M., Woodhouse, C.A., Baisan, C.A., Knight, T., Lukas, J.J., Hughes, M.K., Salzer, M.W., 2007. Medieval drought in the upper Colorado River Basin. Geophys. Res. Lett. 34.

Reconstructed flow data can be found at this website

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Water Supply Climate Change Adaptation Stakeholder Guidebooks

Institution: University of Arizona

Years: 2009 – 2011

PI(s): Colby

Project scientist(s): O’Donnell

Summary: Researchers prepared three guidebooks for stakeholders in the Lower Colorado River Basin. The guidebooks provide practical information for water supply climate change adaptation through water banks, water auctions, dry‐year contracts, and how to implement effective voluntary transactions between agriculture, municipalities and environmental programs to help the Lower Colorado River Basin region cost-effectively adapt to supply variability and extended drought.

Product(s):

Three stakeholder guidebooks:

Entendiendo el Valor del Agua en la Agricultura

Measuring, Monitoring, and Enforcing Temporary Water Transfers: Considerations, Case Examples, Innovations and Costs

Prioritizing Environmental Water Acquisitions: Making the Most of Program Budgets

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Seasonal Predictability in the Gunnison and Little Colorado River Basins

Institution: University of Arizona

Years: 2009 – 2011

PI(s): Troch

Project scientist(s): Switanek

Summary: Attempts were made to improve seasonal climate predictions for the Gunnison and Little Colorado River basins based on leading sea surface temperature (SST) and sea level pressure (SLP) in the most correlated oceanic regions, given a specified forecast outlook time. These most correlated regions’ time series were then used as predictors. Different statistical methods and weighting schemes were used to make the forecasts. Varying weights were applied to particular regions and statistical methods to provide the best forecasts over the time period (1931‐2008). Success was mixed; the forecasts exhibited low skill, but better than that of the Climate Prediction Center forecasts.

Product(s):

Switanek, M.B., Troch, P.A., Castro, C.L., 2009. Improving Seasonal Predictions of Climate Variability and Water Availability at the Catchment Scale. J. Hydrometeorol. 10, 1521–1533.

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Decadal Predictability of Lees Ferry Streamflow Using Teleconnections

Institution: University of Arizona

Years: 2009 – 2011

PI(s): Troch

Project scientist(s): Switanek

Summary: Wavelet power spectra of Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) were used to make retrospective forecasts of the 40 most recent ten-year running means of Lees Ferry streamflow and were found to explain 45% of the observed variance (p<0.01). A similar analysis was done for prehistoric records. Based on existing reconstructions of PDO, AMO and Lee’s Ferry streamflow, skill over the reconstructed periods has rarely been as high as what is seen in the observed record. Based on a wavelet analysis, the three time series all share a dominant multi-decadal frequency between 40 and 70 years in length; however, this multi-decadal frequency is not persistent in time for any of the reconstructed time series.

Product(s):

Switanek, M.B., Troch, P.A., 2011. Decadal prediction of Colorado River streamflow anomalies using ocean-atmosphere teleconnections. Geophys. Res. Lett. 38.

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Extending Tree-ring Chronology in Ninemile Canyon

Institution: University of Arizona

Years: 2009 – 2010

PI(s): Meko

Project scientist(s): Knight, Baisan

Summary: This project developed a 2300-year tree-ring chronology extending to 323 BC using live and remnant Douglas-fir from the Tavaputs Plateau in northeastern Utah. Extreme wet and dry periods without modern analogues were identified in the reconstruction.

Product(s):

Knight, T.A., Meko, D.M., Baisan, C.H., 2010. A Bimillennial-Length Tree-Ring Reconstruction of Precipitation for the Tavaputs Plateau, Northeastern Utah. Quat. Res. 73, 107–117.

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Updating the Critical Period for the Colorado River

Institution: University of Arizona

Years: 2009 – 2010

PI(s): Woodhouse

Project scientist(s): Malevich

Summary: Reclamation has defined two Critical Periods of Record (CPRs) for the Colorado River, a 12- and 25-year period from water year 1953 through 1964, and from 1953 through 1977, respectively, but there is little documentation about how or when these CPR periods were determined. This project used observed and reconstructed Lees Ferry flows to revisit the 12-year CPR. The results, along with a list of drought characteristics from the preliminary record suggest that the drought years of 2000-2009 would replace the drought years of the 1950s and 1960s as the CPR. According to our definition of drought as consecutive years broken by less than two above average years, the drought from 2000 to 2010 is matched in duration by a drought in the 1950s-1960s, but exceeds the cumulative intensity.

Product(s):

Report available upon request

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Long-term Forecasting of Lower Colorado River Tributaries from Multi-decadal Signals

Institution: University of Arizona

Years: 2009 – 2012

PI(s): Troch, Woodhouse, Jacobs, Meko

Project scientist(s): Lambeth-Beagles

Summary: Historical changes in hydroclimatic characteristics in four Lower Colorado River sub-basins are examined using the Mann-Kendall test for trends and Kendall’s tau-b test for statistical association to better understand the processes taking place in these arid watersheds. From 1906 to 2007, in general, temperatures increased and streamflows decreased while there has been no change in precipitation. Streamflow was found to have statistical association with annual maximum temperatures, El Nino Southern Oscillation (ENSO), and Pacific Decadal Oscillation (PDO). Using this knowledge, two-year and five-year streamflow predictions are made using climate data to force a statistical model. We find no predictive skill at the two-year range but significant predictive skill in two of the basins at the five-year range. The dominant climate predictor for the Paria River Basin is ENSO and for the Little Colorado River Basin it is temperature.

Product(s):

Lambeth-Beagles, Rachel (2011) “An Assessment of Hydroclimatic Trends and Mid-Range Streamflow Predictive Capacity in Four Lower Colorado River Sub-Basins”, M.S. Thesis, University of Arizona.

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Hydroclimatic Reconstructions in the Lower Colorado River Basin

Institution: University of Arizona

Years: 2009 – 2012

PI(s): Meko

Project scientist(s): Morino

Summary: This project used a simple scatterplot-smoothing model applied in a three-stage reconstruction procedure to develop multi-century reconstructions for several tributaries in the Lower Basin. Depending on quantity and quality of data, either precipitation or streamflow was produced. Analysis showed that combined flow of the Virgin and Little Colorado Rivers into Lake Mead exceeded 500,000 acre-feet 15% of the time. Dry spells in the Lower Basin reconstructions tend to be synchronous with dry spells in the Upper Basin reconstructions, but wet spells are less synchronous across the two basins.

Product(s):

Report available upon request

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Using Paleohydrology to Inform Water Management under Climate Change

Institution: University of Arizona

Years: 2009 – 2011

PI(s): Meko

Project scientist(s): Morino

Summary: The multi-decadal drought of the mid-1100s (identified using a 1244-year reconstruction of annual Lees Ferry flows) was used to analyze the effects that streamflow variability could have on reservoir levels in the Colorado River Basin. Under such drought conditions and using the operations put in place during the 2007 Interim Guidelines, Lake Mead elevation would likely reach dead pool within 25 years.

Product(s):

Meko, D., Woodhouse, C., Morino, K., 2012. Dendrochronology and links to streamflow. J. Hydrol. 412–413, 200–209.

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Upper Colorado River Basin Drought Catalog and Climate Diagnostics

Institution: University of Arizona

Years: 2009 – 2012

PI(s): Woodhouse

Project scientist(s): Glueck, Malevich, Faulstich

Summary: This study documents the characteristics of Upper Colorado River Basin (UCRB) drought, the circulation patterns that accompany the droughts, and their possible causal mechanisms on an individual drought event basis. This catalog of droughts provides evidence for a range of drought characteristics and accompanying atmosphere/ocean circulation features, and a potential baseline for evaluating future droughts. Analysis showed that the droughts of the UCRB are widely varied in terms of temporal and spatial characteristics, and that different sequences of a large number of circulation patterns and mechanisms combine to produce multi-year droughts.

Product(s):

Report available upon request

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A New Approach for Using Tree-ring Data in Water Management Planning on the Colorado River

Institution: University of Arizona

Years: 2009 – 2012

PI(s): Meko

Project scientist(s): Morino, Bark

Summary: Modeling to evaluate system response to paleohydrology is often carried out by testing the system under two types of streamflow scenarios. The first approach is based on a period with the worst mean streamflow which represents a “worst case scenario”, and the second approach uses the entire paleo record. This work proposes and demonstrates a method that takes advantage of the wider range of variability in sequence and mean flow that are present in tree ring data by identifying periods of the paleorecord with similar but lower-than-average mean streamflow which are then grouped and taken to represent different future streamflow scenarios. These “worsening-case scenarios” can help develop a more structured view of system vulnerabilities. A system response variable – total deficit (due to elevation-dependent shortages) – was used to organize and prioritize streamflow information associated with different levels of shortage severity. These results highlight two important features of the Colorado River system: 1) current reservoir conditions dictate that streamflow levels over the next decade can be informative in projecting deficit levels 30 years into the future; and 2) under drier streamflow regimes, the ability to project future deficit increases.

Product(s):

Report available upon request

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Customized Circulation Indices for the Upper Colorado River Basin

Institution: University of Arizona

Years: 2013 – 2016

PI(s): Woodhouse

Project scientist(s): Morino

Summary: This study used two-stage correlation analysis to evaluate a suite of ocean-circulation variables to identify any associations to cool season precipitation at high elevations in the Upper Colorado River Basin (UCRB). The goal was to build a custom circulation index that explains significant variability. The early cool season (Oct-Dec) exhibited stronger association with atmospheric circulation compared with the late cool season (Jan-Mar). Two atmospheric locations that have previously been associated with UCRB drought and snowpack were found to have strong teleconnections to upper elevation precipitation: Aleutian Low and the western United States high. Evaluating performance of different configurations of custom indices developed in this study resulted in potentially important implications for the use of circulation indices in water planning and recommendations for additional work.

Product(s):

Report available upon request

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Understanding the Impact of Inhomogeneous Temperature Data on Streamflow Analyses

Institution: University of Arizona

Years: 2013 – 2016

PI(s): Woodhouse

Project scientist(s): Morino

Summary: Two gridded data products were used to quantify the temporal and spatial stability of temperature relationships with Lees Ferry streamflow: Parameter-elevation Relationships on Independent Slopes Model (PRISM) and TopoWx. Stepwise linear regression was used to identify important temperature predictors, and the stability of predictors was checked by comparing their statistical significance in the early and late parts of the record. Results showed that different conclusions could be drawn about the importance of spring temperatures to annual streamflow depending on which dataset was used in developing regression models, especially during more recent decades.

Product(s):

Report available upon request

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Designing Effective and Implementable Economic Tools for Climate Adaptation and Improved Supply Reliability

Institution: University of Arizona

Years: 2013 – 2016

PI(s): Colby

Project scientist(s): NA

Summary: This study reviewed and conducted surveys to support the design of potential future Reclamation system conservation programs. It particularly focused on costs of such programs to farmers and water districts and optimal timing. It researched existing system conservation programs to identify how water use baselines (before conservation) were designed and used.

Product(s):

Report available upon request

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Enhancing Capacity for the Use of Climate Change Science in Decision Making

Institution: University of Arizona

Years: 2013 – 2016

PI(s): Garfin

Project scientist(s): NA

Summary: Based on input from water managers from the Upper and Lower Colorado River Basins, two workshops exploring practical impacts of climate change were conducted. The first workshop focused on research and management needs related to severe fires and post-fire flooding in the Intermountain West. The second workshop focused on the cascading effects of constrained water resources, extreme summer heat, and disruptions to energy production and transmission. Each workshop developed research, data, and management needs as well as recommendations for developing a flood assessment and management toolkit (first workshop) and creating and maintaining institutional knowledge to deal with high consequence, low probability events (second workshop).

Product(s):

Garfin, G., S. LeRoy, D. Martin, M. Hammersley, A. Youberg, and R. Quay. 2016. Managing for Future Risks of Fire, Extreme Precipitation, and Post-fire Flooding. Report to the U.S. Bureau of Reclamation, from the project Enhancing Water Supply Reliability. Tucson, AZ: Institute of the Environment, 33 p.

Garfin, G., S. LeRoy, B. McMahan, M. Black, and B. Roh. 2016. Preparing for High Consequence, Low Probability Events: Heat, Water & Energy in the Southwest. Report to the U.S. Bureau of Reclamation, from the project Enhancing Water Supply Reliability. Tucson, AZ: Institute of the Environment, 30 p.

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Colorado River Basin Streamflow Projection under IPCC Scenarios: from the Global to Basin Scale Using an Integrated Dynamic Modeling Approach

Institution: University of Arizona

Years: 2013 – 2016

PI(s): Castro, Troch

Project scientist(s): Chang, Carillo, Mukherjee

Summary: This study compared the streamflow projections resulting from dynamical downscaling using Regional Climate Models (RCMs) to those generated using Bias Correction and Spatial Disaggregation (BCSD) to assess whether the level of downscaling complexity has a significant impact on streamflow used for operational planning purposes. It also evaluated whether RCMs could provide improved representation of natural climate variability in the Western U.S. over General Circulation Models (GCMs) by downscaling a selection of GCM projections and a historical 20th century atmospheric reanalysis. Among other results, this study found that downscaling complexity makes a substantial difference in streamflow projections; dynamical downscaling results in larger streamflow decreases in both Coupled Model Intercomparison Project (CMIP) phase 3 (CMIP3) and CMIP5 models than BCSD.

Product(s):

Chang, H.-I., Castro, C.L., Carrillo, C.M., Dominguez, F., 2015. The more extreme nature of U.S. warm season climate in the recent observational record and two “well-performing” dynamically downscaled CMIP3 models. J. Geophys. Res. Atmospheres 120, 8244–8263.

Carrillo, C.M., Castro, C.L., Chang, H.-I., Luong, T.M., 2017. Multi-year climate variability in the Southwestern United States within a context of a dynamically downscaled twentieth century reanalysis. Clim. Dyn. 49, 4217–4236.

Mukherjee, R. (2016) “Implications of statistical and dynamical downscaling methods on streamflow projections for the Colorado River Basin”, M.S. Thesis, University of Arizona.

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Evaluation of Inter-annual and Inter-decadal Influences on Snow and Streamflow

Institution: University of Nevada Las Vegas

Years: 2007 - 2008

PI(s): Piechota

Project scientist(s): Miller, Lamb, Wang

Summary: This project studied trends in historical monthly temperature, precipitation, snowpack, and streamflow. In general: temperatures increased persistently throughout the year across the basin; precipitation only increased in parts of the basin and only in February; streamflow increased during the November through February period but decreased over the April through July period. Analyses did not show any trend in frequency of snowfall and rainfall events, but the basin is experiencing decreased snowpack and earlier snowmelt.

Product(s):

Miller, W.P., Piechota, T.C., 2008. Regional Analysis of Trend and Step Changes Observed in Hydroclimatic Variables around the Colorado River Basin. J. Hydrometeorol. 9, 1020–1034.

Miller, W.P., Piechota, T.C., 2011. Trends in Western U.S. Snowpack and Related Upper Colorado River Basin Streamflow. JAWRA J. Am. Water Resour. Assoc. 47, 1197–1210.

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Modeling Streamflow Using the National Weather Service River Forecasting System

Institution: University of Nevada Las Vegas

Years: 2008 - 2012

PI(s): Piechota

Project scientist(s): Miller

Summary: Projections of streamflow over the Green, Gunnison, and San Juan River headwater basins are generated by forcing the National Weather Service River Forecast System (NWSRFS) with downscaled climate data with a particular focus on the impact of changing evapotranspiration rates. The resulting streamflow projections show decreased runoff in the Gunnison and San Juan basins and an increase in the Green. An evaluation on the impacts that hydrologic model choice can have on critical decision variables within the San Juan basin was performed, comparing streamflow projections from the Variable Infiltration Capacity (VIC) model with projections from NWSRFS. The impact was significant; VIC flows were 15% higher than NWSRFS in the upper watershed and 25% higher at the confluence with the Colorado River.

Product(s):

Miller, W.P., Piechota, T.C., Gangopadhyay, S., Pruitt, T., 2011. Development of streamflow projections under changing climate conditions over Colorado River basin headwaters. Hydrol. Earth Syst. Sci. 15, 2145–2164.

Miller W. Paul, Butler R. Alan, Piechota Thomas, Prairie James, Grantz Katrina, DeRosa Gina, 2012. Water Management Decisions Using Multiple Hydrologic Models within the San Juan River Basin under Changing Climate Conditions. J. Water Resour. Plan. Manag. 138, 412–420.

Miller, W. P. (2010) “Assessment of impacts to hydroclimatology and river operations due to climate change over the Colorado River Basin”, Ph.D. Dissertation, University of Nevada Las Vegas.

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Impacts of Changing Water Demands in the Lower Colorado River Basin under Different Climate Scenarios

Institution: University of Nevada Las Vegas

Years: 2010 - 2012

PI(s): Piechota

Project scientist(s): Bunk

Summary: This study used historical and projected hydroclimatic variables such as temperature, wind, and precipitation, to analyze their impacts on riparian evapotranspiration (ET) and reservoir evaporation along the lower Colorado River. Combined evaporative demands have increased by 1.8% during the 30-year period ending in 2010 and may increase by an additional 2% during the 2031-2060 period when compared to the 1951-1980 period. Projected increases in evaporative demands are projected to reduce the combined storage of Lake Powell and Lake Mead by a cumulative volume of 75,400 acre-feet, or 0.15 percent of total conservation capacity, based on 10-year running averages from 2020 to 2060.

Product(s):

Bunk, D. (2012) “Changing Demands from Riparian Evapotranspiration and Free-water Evaporation in the Lower Colorado River Basin Under Different Climate Scenarios”, M.S. Thesis, University of Nevada Las Vegas.

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Modeling Techniques to Assess Long-term Reliability of Environmental Flows in Basin Scale Planning

Institution: University of Colorado, Center for Advanced Decision Support for Water and Environmental Systems (CADSWES)

Years: 2009 - 2011

PI(s): Zagona

Project scientist(s): Butler

Summary: Long term modeling studies are necessary to adequately assess the effectiveness of environmental flows (e-flows). To perform such studies, three issues must be overcome: the timescale discrepancy – e-flows are often defined as daily requirements while long term models run at monthly timesteps; the necessity of using daily unregulated tributary flows to model reservoir operations; and the need to incorporate hydrologic year types that guide reservoir operations to meet e-flow targets. This study successfully incorporated daily reservoir requirements into a monthly model and used a flow alteration metric and multiple supply and demand scenarios to demonstrate their use under a nonstationary climate.

Product(s):

Butler, R. A. (2011) “Modeling Techniques to Assess Long-term Reliability of Environmental Flows in Basin Scale Planning”, M.S. Thesis, University of Colorado Boulder.

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Seasonal and Interannual Stochastic Streamflow Simulation and Probabilistic Operations Modeling

Institution: University of Colorado, Center for Advanced Decision Support for Water and Environmental Systems (CADSWES)

Years: 2009 - 2011

PI(s): Rajagopalan, Zagona

Project scientist(s): Bracken

Summary: This project addressed four topics: seasonal forecasting, interannual forecasting, annual flow simulation, and water supply management modeling. To try to improve seasonal forecasting, climate information was combined with snowpack and soil moisture data to produce seasonal forecasts starting in November instead of January. A Hidden Markov (HM) analysis showed that there is persistent regime-switching behavior in the Lees Ferry natural flow timeseries, suggesting that long droughts are more likely to occur than previously thought. The HM model produced annual streamflow forecasts that had greater skill than climatology. A model capable of using ensemble streamflow forecasts called the Mid-Term probabilistic Operations Model (MTOM) was created to determine the value of the newly-developed seasonal and annual forecasting techniques.

Product(s):

Bracken, C., Rajagopalan, B., Prairie, J., 2010. A multisite seasonal ensemble streamflow forecasting technique. Water Resour. Res. 46.

Bracken, Cameron W. (2011) “Seasonal to Inter-Annual Streamflow Simulation and Forecasting on the Upper Colorado River Basin and Implications for Water Resources Management”, M.S. Thesis, University of Colorado.

Bracken, C., Rajagopalan, B., Zagona, E., 2014. A hidden Markov model combined with climate indices for multidecadal streamflow simulation. Water Resour. Res. 50, 7836–7846.

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Spatial and Temporal Streamflow Disaggregation

Institution: University of Colorado, Center for Advanced Decision Support for Water and Environmental Systems (CADSWES)

Years: 2009 - 2011

PI(s): Rajagopalan, Zagona

Project scientist(s): Nowak

Summary: This work was motivated by the need to generate plausible synthetic streamflow data that allows users to explore conditions beyond the magnitude and duration of historical extremes. An additional consideration was that the data must correspond to the timestep and spatial layout of a relevant model. The nonparametric proportional disaggregation technique developed here enables users to create synthetic data at a regional, annual timestep and disaggregate it coherently to multiple sites at a daily timestep in a computationally efficient way that preserves statistical relationships at the different scales.

Product(s):

Nowak, K., Prairie, J., Rajagopalan, B., Lall, U., 2010. A nonparametric stochastic approach for multisite disaggregation of annual to daily streamflow. Water Resour. Res. 46.

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Interdecadal Variability and Stochastic Simulation of Lees Ferry Annual Streamflow

Institution: University of Colorado, Center for Advanced Decision Support for Water and Environmental Systems (CADSWES)

Years: 2009 - 2011

PI(s): Rajagopalan, Zagona

Project scientist(s): Nowak

Summary: Wavelet-based spectral analysis was applied to historical Lees Ferry annual streamflow. Two significant modes of multidecadal variability were identified: a low-frequency mode associated with the effects of temperature on runoff efficiency and a decadal frequency mode associated with moisture delivery that has only been active in recent decades. Paleo-reconstructed flow also exhibited these characteristics. A novel Wavelet-based Auto Regression Model (WARM) framework was developed to incorporate these variability findings into multisite stochastic streamflow simulations.

Product(s):

Nowak, K.C., Rajagopalan, B., Zagona, E., 2011. Wavelet Auto-Regressive Method (WARM) for multi-site streamflow simulation of data with non-stationary spectra. J. Hydrol. 410, 1–12.

Nowak, Kenneth C. (2011) “Stochastic Streamflow Simulation at Interdecadal Times Scales and Implications for Water Resources Management in the Colorado River Basin”, Ph.D. Thesis, University of Colorado.

Nowak, K., Hoerling, M., Rajagopalan, B., Zagona, E., 2012. Colorado River Basin Hydroclimatic Variability. J. Clim. 25, 4389–4403.

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Analysis of Colorado River Basin Drought Probability

Institution: University of Colorado, Center for Advanced Decision Support for Water and Environmental Systems (CADSWES)

Years: 2009 - 2011

PI(s): Rajagopalan, Zagona

Project scientist(s): Nowak

Summary: A peer-reviewed 2008 article authored by Barnett and Pierce drew dramatic conclusions about future water supply risks on the Colorado River. This project performed a new analysis that addressed improper assumptions and overlooked factors such as evaporation and intervening flows and also provided a more nuanced discussion of natural flow variability and management mechanisms. Additional modeling explored the relative impacts of demand growth and potential climate change-induced flow reductions, finding that the flow reductions greatly increased probability of reservoir depletion but that flexible management could partially address the risk.

Product(s):

Barsugli, J.J., Nowak, K., Rajagopalan, B., Prairie, J.R., Harding, B., 2009. Comment on “When will Lake Mead go dry?” by T. P. Barnett and D. W. Pierce. Water Resour. Res. 45.

Rajagopalan, B., Nowak, K., Prairie, J., Hoerling, M., Harding, B., Barsugli, J., Ray, A., Udall, B., 2009. Water supply risk on the Colorado River: Can management mitigate? Water Resour. Res. 45.

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Stochastic Streamflow Simulation, Multidecadal Streamflow Predictability, and Applying Decadal Projections to Operational Decision Making

Institution: University of Colorado, Center for Advanced Decision Support for Water and Environmental Systems (CADSWES)

Years: 2012 - 2015

PI(s): Rajagopalan, Zagona

Project scientist(s): Erkyihun

Summary: This work demonstrated a new method of combining wavelet analysis and KNN bootstrapping to incorporate skill from climate indices into stochastic streamflow simulations of Lees Ferry annual flow. The simulations reproduced nonstationarity characteristics and showed skill at decadal and multidecadal timeframes. The study also used Local Lyapunov Exponents (LLE) to quantify time-varying predictability in Lees Ferry annual streamflow. While there is predictability, it varies over different epochs. With this information, ensembles of decadal projections were developed and used to modify long term planning decision criteria from the Colorado River Basin Water Supply and Demand Study.

Product(s):

Erkyihun, Solomon Tassew (2015) “Multi-decadal Stochastic Streamflow Projections and Application to Water Resources Decision Making in the Colorado River Basin”, Ph.D. Thesis, University of Colorado.

Erkyihun, S.T., Rajagopalan, B., Zagona, E., Lall, U., Nowak, K., 2016. Wavelet-based time series bootstrap model for multidecadal streamflow simulation using climate indicators. Water Resour. Res. 52, 4061–4077.

Erkyihun S.T., Zagona E., Rajagopalan B., 2017. Wavelet and Hidden Markov-Based Stochastic Simulation Methods Comparison on Colorado River Streamflow. J. Hydrol. Eng. 22.

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A Nonparametric Approach to Paleohydrology Reconstruction

Institution: AMEC

Years: 2006 - 2008

PI(s): Harding, Gangopadhyay

Project scientist(s): NA

Summary: This work presents the first nonparametric method developed to reconstruct streamflow ensembles from tree ring chronology. The project used tree rings from the period 1400 – 2005 and naturalized streamflow from the period 1906 – 2005. The method compares very well with observed flows and other reconstructions and provides a more realistic confidence interval than other methods.

Product(s):

Gangopadhyay, S., Harding, B.L., Rajagopalan, B., Lukas, J.J., Fulp, T.J., 2009. A nonparametric approach for paleohydrologic reconstruction of annual streamflow ensembles. Water Resour. Res. 45.

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Downscaled CMIP3 Colorado River Basin Streamflow Projections

Institution: AMEC

Years: 2008 - 2010

PI(s): Harding, Gangopadhyay

Project scientist(s): NA

Summary: Downscaled outputs of 112 climate projections from 16 climate models were used to drive the Variable Infiltration Capacity (VIC) hydrologic model. This output was routed and bias corrected in order to be used as input to the Colorado River Simulation System (CRSS). Analysis showed a wide range of potential streamflow futures, both dry and wet, primarily due to the uncertainty in future precipitation. The large ensemble analysis in this project provides perspective on studies that used fewer scenarios.

Product(s):

Harding, B.L., Wood, A.W., Prairie, J.R., 2012. The implications of climate change scenario selection for future streamflow projection in the Upper Colorado River Basin. Hydrol. Earth Syst. Sci. 16, 3989–4007.

Dataset of 112 CMIP3 projections (available upon request)

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Homogeneity Analysis of Precipitation from Three Gridded Products

Institution: National Oceanic and Atmospheric Administration (NOAA), Cooperative Institute for Research in Environmental Sciences (CIRES), Western Water Assessment (WWA)

Years: 2007 - 2009

PI(s): Barsugli, Eischeid, Raff, Brekke

Project scientist(s): Guentchev

Summary: Three gridded precipitation products (Maurer et al., that of Beyene and Lettenmaier, and the Parameter–Elevation Regressions on Independent Slopes Model (PRISM) dataset of Daly et al.) were evaluated to determine how the gridding process and using inhomogeneous station data affect trends and variability. Potential explanations are offered for notable breaks in the datasets. The study concluded that timeseries from all three datasets are homogeneous enough for use in variability analysis over the 1950-1999 period.

Product(s):

Guentchev, G., Barsugli, J.J., Eischeid, J., 2010. Homogeneity of Gridded Precipitation Datasets for the Colorado River Basin. J. Appl. Meteorol. Climatol. 49, 2404–2415.

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Examining Climate Change in the Colorado Rocky Mountains Using High-resolution Climate Models

Institution: National Oceanic and Atmospheric Administration (NOAA), Cooperative Institute for Research in Environmental Sciences (CIRES), Western Water Assessment (WWA)

Years: 2009 - 2011

PI(s): Rangwala

Project scientist(s): NA

Summary: Dynamically-downscaled temperature and precipitation projections for the San Juan Mountains region were examined in detail. A total of six different combinations of Regional Climate Models (RCMs) and General Circulation Models (GCMs) using the A2 Representative Concentration Pathway (RCP) from the North American Regional Climate Change Assessment Program (NARCCAP) database were used. Temperature minimums and maximums were analyzed by season and elevation, finding that by mid 21st century, all seasons and elevations could experience an increase of at least 4°F for both minimum and maximum temperatures. More extreme increases were also projected and potential reasons for these extremes were considered. Precipitation was analyzed at seasonal and monthly scales. None of the RCMs captured the observed seasonality of precipitation in the region. The RCMs generally agree with native-scale GCM projections except that some RCMs show greater reductions in summer precipitation.

Product(s):

Cozzetto, K., I. Rangwala and J. Lukas, (2011). Examining Regional Climate Model (RCM) projections: What do they add to our picture of future climate in the region? Featured article in the July issue of “Intermountain West Climate Summary” by NOAA’s Western Water Assessment

Nydick, K., Crawford, J., Bidwell, M., Livensperger, C., Rangwala, I., and Cozetto, K. 2012. Climate Change Assessment for the San Juan Mountain Regions, Southwestern Colorado, USA: A Review of Scientific Research

Rangwala, I., Barsugli, J., Cozzetto, K., Neff, J., Prairie, J., 2012. Mid-21st century projections in temperature extremes in the southern Colorado Rocky Mountains from regional climate models. Clim. Dyn. 39, 1823–1840.

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Evaluating High-altitude Precipitation and Temperature

Institution: National Oceanic and Atmospheric Administration (NOAA), Cooperative Institute for Research in Environmental Sciences (CIRES), Western Water Assessment (WWA)

Years: 2009 - 2011

PI(s): Rangwala

Project scientist(s): NA

Summary: National Weather Service observations and Snow Telemetry (SNOTEL) data from 1895 to 2005 for the San Juan Mountains (SJM) were used to investigate spatial and temporal trends in minimum and maximum temperatures. Analyses found a cooling trend from 1950 to 1985 and that most of the warming between 1895 and 2005 has occurred since 1990. The warming in Western Colorado, including the SJM, is one of the highest in the country and greater than the global land average. To investigate whether this is due to a difference in how climate change is affecting mountainous regions, four high mountain regions, including the Rocky Mountains, were analyzed. Several mechanisms and processes that could result in enhanced warming at higher elevations were described, but the study could not draw strong conclusions about whether and why this might occur. Further investigation of the concept focusing on Tibetan Plateau found that increases in atmospheric water vapor, which amplifies the effect of longwave downward radiation, are elevation-sensitive. This may contribute to the overall sensitivity of mountainous regions to climate change and indicate possible enhanced winter‐time warming caused by a continued moistening of the atmosphere as a result of increases in the anthropogenic greenhouse gas forcing during this century.

Product(s):

Rangwala, I., Miller, J.R., 2010. Twentieth Century Temperature Trends in Colorado’s San Juan Mountains. Arct. Antarct. Alp. Res. 42, 89–98.

Rangwala I. and J. Miller, 2011. Long-Term Temperature Trends In The San Juan Mountains. In EASTERN SAN JUAN MOUNTAINS: Their Geology, Ecology and Human History, edited by Rob Blair and George Bracksieck, University Press of Colorado (pp.99-112).

Rangwala, I., Miller, J.R., 2012. Climate change in mountains: a review of elevation-dependent warming and its possible causes. Clim. Change 114, 527–547.

Rangwala, I., 2013. Amplified water vapour feedback at high altitudes during winter. Int. J. Climatol. 33, 897–903.

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