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Climate, Growth and Drought Threat to Colorado River Water Supply

Climate, Growth and Drought Threat to Colorado River Water Supply. Balaji Rajagopalan Department of Civil, Environmental and Architectural Engineering And Cooperative Institute for Research in Environmental Sciences (CIRES) University of Colorado Boulder, CO Presentation to KOWACO

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Climate, Growth and Drought Threat to Colorado River Water Supply

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  1. Climate, Growth and Drought Threat to Colorado River Water Supply Balaji Rajagopalan Department of Civil, Environmental and Architectural Engineering And Cooperative Institute for Research in Environmental Sciences (CIRES) University of Colorado Boulder, CO Presentation to KOWACO February 3, 2009

  2. Collaborators • Kenneth Nowak - CEAE / CADSWES • Edith Zagona - CADSWES • James Prairie - USBR, Boulder • Ben Harding - AMEC, Boulder • Marty Hoerling - NOAA • Joe Barsugli - CIRES/WWA/NOAA • Brad Udall - CIRES/WWA/NOAA • Andrea Ray - NOAA

  3. Inter-decadal Climate Decision Analysis: Risk + Values Time Horizon • Facility Planning • Reservoir, Treatment Plant Size • Policy + Regulatory Framework • Flood Frequency, Water Rights, 7Q10 flow • Operational Analysis • Reservoir Operation, Flood/Drought Preparation • Emergency Management • Flood Warning, Drought Response Data: Historical, Paleo, Scale, Models Weather Hours A Water Resources Management Perspective

  4. Modeling Framework What Drives Year to Year Variability in regional Hydrology? (Floods, Droughts etc.) Diagnosis Hydroclimate Predictions – Scenario Generation (Nonlinear Time Series Tools, Watershed Modeling) Forecast Decision Support System (Evaluate decision strategies Under uncertainty) Application

  5. Resources • http://cadswes.colorado.edu/publications • (PhD thesis) • Regonda, 2006 • Prairie, 2006 • Grantz, 2006 • Stochastic Streamflow Simulation • http://animas.colorado.edu/~prairie/ • http://animas.colorado.edu/~nowakkc/ • balajir@colorado.edu • jprairie@uc.usbr.gov

  6. Colorado River Basin Overview 7 States, 2 Nations Upper Basin: CO, UT, WY, NM Lower Basin: AZ, CA, NV Fastest Growing Part of the U.S. Over 1,450 miles in length Basin makes up about 8% of total U.S. lands Highly variable Natural Flow which averages 15 MAF 60 MAF of total storage 4x Annual Flow 50 MAF in Powell + Mead Irrigates 3.5 million acres Serves 30 million people Very Complicated Legal Environment Denver, Albuquerque, Phoenix, Tucson, Las Vegas, Los Angeles, San Diego all use CRB water DOI Reclamation Operates Mead/Powell Source:Reclamation 1 acre-foot = 325,000 gals, 1 maf = 325 * 109 gals 1 maf = 1.23 km3 = 1.23*109 m3

  7. Water Budget Analysis One 50 maf reservoir, increasing UB demands (13.5 in 2008 ->14.1 Maf/yr in 2030, 15.1 maf /yr inflows, current starting contents Linear Climate Change Reduction in Flows w/ some natural variability Results With Linear 20% Reduction in mean flows Over 50 years 10% Chance Live Storage Gone by 2013 50% Chance Live Storage Gone by 2021 50% Chance Loss of Power by 2017 Is that so? When Will Lake Mead Go Dry?Barnett & Pierce, Water Resources Research, 2008

  8. Colorado River Demand - Supply

  9. Declining Lakes Mead and Powell 120 Foot drop13 maf lostCurrent: ~48%, 12 maf 5 Years of 10 maf/yr66% of average flowsWorst drought in historic record 75 Foot Drop (Max 140)10.5 maf lost Current: ~56%, 14.5 maf

  10. New York Times Sunday Magazine, October 21, 2007

  11. Dropping Lake Mead Lake Powell – June 29, 2002 Lake Powell – December 23, 2003 Lake Mead’s Delta Circa 1999 ~2004 ~1999 Source: USGS, Reclamation

  12. Below normal flows into Lake Powell 2000-2004 62%, 59%, 25%, 51%, 51%, respectively 2002 at 25% lowest inflow recorded since completion of Glen Canyon Dam Some relief in 2005 105% of normal inflows Not in 2006 ! 73% of normal inflows 2007 at 68% of Normal inflows 2008 at 111% of Normal inflows Recent conditions in the Colorado River BasinPaleo Context Colorado River at Lees Ferry, AZ 5 year running average

  13. observed record Woodhouse et al. 2006 Stockton and Jacoby, 1976 Hirschboeck and Meko, 2005 Hildalgo et al. 2002

  14. Past Flow Summary • Paleo reconstructions indicate • 20th century one of the most wettest • Long dry spells are not uncommon • 20-25% changes in the mean flow • Significant interannual/interdecadal variability • Rich variety of wet/dry spell sequences • All the reconstructions agree greatly on the ‘state’ (wet or dry) information • How will the future differ? • More important, What is the water supply risk under changing climate?

  15. Future Climate

  16. The Fundamental Problem with Climate Change For Water Management All water resource planning based on the idea of “climate stationarity” – climate of the future will look like the climate of the past. Reservoir sizing Flood Control Curves System Yields Water Demands Urban Runoff Amounts This will be less and less true as we move forward. Existing Yields now not as certain given both supply and demand changes New water projects have an additional and new element of uncertainty. Science, February 1, 2008 Stuff and m

  17. IPCC 2007 AR4 Projections Wet get wetter and dry get drier… Southwest Likely to get drier

  18. Models Precip and Temp Biases Models show consistent errors (biases) Western North America is too cold and too wet Weather models show biases, too Can be corrected

  19. A Large Number of Studies Point to a Drying American Southwest “From 2040 to 2060, anticipated water flows from rainfall in much of the West are likely to approach a 20 percent decrease in the average from 1901 to 1970, and are likely to be much lower in places like the fast-growing Southwest.” ~ May 28, 2008, New York Times Milly et al., 2005 Seager et a.l, 2007 IPCC WG1, IPCC WG2, 2007 National Academy Study, 2007 IPCC Water Report, 2008 CCSP SAP 4.3, 2008

  20. Regression CRSSCRMM Hydrology Models:NWSRFSVICPRMS Hypothetical Scenarios Progression of Data and Models in studies about the influence of climate change on streamflows in the Colorado River Basin 3.Water Supply Operations Model 1.Climate Change Data Source 2.Flow Generation Technique General CirculationModel Temperature Precipitation Streamflow OR Reservoir storage Hydroelectric powerUB Releases Stuff and m

  21. Precipitation, Temperatures and Runoff in 2070-2099 CRB Runoff From C&L ~115% Triangle size proportional to runoff changes: Up = Increase Down = Decrease Green = 2010-2039 Blue = 2040-2069 Red = 2070-2099 -40% to +30% Runoff changes in 2070-2099 ~80% 2C to 6 C

  22. Colorado River Climate Change Studies over the Years Early Studies – Scenarios, About 1980 Stockton and Boggess, 1979 Revelle and Waggoner, 1983* Mid Studies, First Global Climate Model Use, 1990s Nash and Gleick, 1991, 1993 McCabe and Wolock, 1999 (NAST) IPCC, 2001 More Recent Studies, Since 2004 Milly et al.,2005, “Global Patterns of trends in runoff” Christensen and Lettenmaier, 2004, 2006 Hoerling and Eischeid, 2006, “Past Peak Water?” Seager et al, 2007, “Imminent Transition to more arid climate state..” IPCC, 2007 (Regional Assessments) Barnett and Pierce, 2008, “When will Lake Mead Go Dry?” National Research Council Colorado River Report, 2007

  23. Almost all the water is generated from a small region of the basin at very • high altitude • GCM projections for the high altitude regions are uncertain

  24. Future Flow Summary • Future projections of Climate/Hydrology in the basin based on current knowledge suggest • Increase in temperature with less uncertainty • Decrease in streamflow with large uncertainty • Uncertain about the summer rainfall (which forms a reasonable amount of flow) • Unreliable on the sequence of wet/dry (which is key for system risk/reliability) • The best information that can be used is the projected mean flow

  25. Water Supply System Risk Estimation Streamflow Scenarios Conditioned on climate change projections Water Supply Model Management + Demand growth alternatives System Risk Estimates For each year

  26. Streamflow Simulation • Paleo • Observations • Need to Combine

  27. Need to Combine Paleo and Observed flows for stochastic simulation • Colorado River System has enormous storage of approx 60MAF ~ 4 times the average annual flow - consequently, • wet and dry sequences are crucial for system risk/reliability assessment • Streamflow generation tool that can generate flow scenarios in the basin that are realistic in • wet and dry spell sequences • Magnitude • Paleo reconstructions are • Good at providing ‘state’ (wet or dry) information • Poor with the magnitude information • Observations are reliable with the magnitude • Need for combining all the available information • Observed Annual average flow (15MAF) is used to define wet/dry state.

  28. Generate system state Generate flow conditionally (K-NN resampling of historical flow) Proposed Framework Prairie et al. (2008, WRR) Nonhomogeneous Markov Chain Model on the observed & Paleo data Natural Climate Variability 10000 Simulations Each 50-year long 2008-2057 Superimpose Climate Change trend (10% and 20%) Climate Change

  29. window = 2h +1 Discrete kernel function h Source: Rajagopalan et al., 1996

  30. Nonhomogenous Markov model with Kernel smoothing (Rajagopalan et al., 1996) • Transition Probability (TP) for each year are obtained using a discrete Kernel Estimator • h determined with LSCV • 2 state, lag 1 model was chosen • ‘wet (1)’ if flow above annual median of observed record; ‘dry (0)’ otherwise. • AIC used for order selection (order 1 chosen)

  31. Transition Probabilities

  32. Generate flow conditionally (K-NN resampling of historical flow) Simulation • Re-sample a block of years (as desired for planning – say 50 year) • Using the TP for each year generate a ‘state’ (St) • Conditionally Re-sample a streamflow magnitude from the observed flow • Identify K-nearest neighbors from the observations to the ‘feature vector’ (St , St-1 and xt ) • Re-sample one of the neighbor – i.e., one of the years, say year j • Flow of year j+1 is the simulated flow, Xt+1

  33. Drought and Surplus Statistics Surplus Length Surplus volume flow Drought Length Threshold (e.g., median) time Drought Deficit

  34. K-NN-1 bootstrap Of observed flow Paleo + Obs Drought/Surplus Statistics Red  Paleo stat Blue  Observed stat

  35. Storage Statistics 60

  36. System Risk • Streamflow Simulation • System Water Balance Model • Management Alternatives • (Reservoir Operation + Demand Growth)

  37. Lees Ferry, AZ gauge Demarcates Upper and Lower Basin 90% of the entire basin flow passes through this gauge Well maintained gauge Annual Average flow is about 15MaF Sizeable flow occurs between Lake Powell and Mead ~ 750KaF/year Small but useful flow below Mead also comes in to the system ~ 250KaF/year UC CRSS stream gauges LC CRSS stream gauges

  38. Storage in any year is computed as: • Storage = Previous Storage + Inflow - ET- Demand • Upper and Lower Colorado Basin demand = 13.5 MAF/yr • Total Active Storage in the system 60 MAF reservoir • Initial storage of 30 MAF (i.e., current reservoir content) • Inflow values are natural flows at Lee’s Ferry, AZ + Intervening flows between Powell and Mead and below Mead • ET computed using Lake Area – Lake volume relationship and an average ET coefficient of 0.436 • Transmission Losses ~6% of Releases Water Balance Model

  39. 2 1.5 ET (MaF) 1 0.5 0 0 10 20 30 40 50 60 70 Storage (MaF) Combined Area-volume RelationshipET Calculation ET coefficients/month (Max and Min) 0.5 and 0.16 at Powell 0.85 and 0.33 at Mead Average ET coefficient : 0.436 ET = Area * Average coefficient * 12

  40. Management and Demand Growth Combinations A. The interim EIS operational policies employed with demand growing based on the upper basin depletion schedule. B with the demand fixed at the 2008 level ~ 13.5MaF C. Same as A but with larger delivery shortages D. Same as C but with a 50% reduced upper basin depletion schedule. E. Same as A with full initial storage. F. Same as A but post 2026 policy that establishes new shortage action thresholds and volumes. G. Demand fixed at 2008 level and post 2026 new shortage action. All the reservoir operation policies take effect from 2026

  41. Flow and Demand Trendsapplied to the simulations Blue – mean flow trend 15MAF – 12MAF By 2057 -0.06MAF/year Under 20% - reduction Red – demand trend 13.5MAF – 14.1MAF by 2030

  42. Flow trend with sample simulation 37.2% of simulations > 15MAF 22.3% of simulations > 17MAF 34.7% of simulations > 15MAF 18.8% of simulations > 17MAF

  43. PDF of generated streamflows (boxplots) PDF of observed flow (red) AR-1 NHMM

  44. Natural Climate Variability

  45. Climate Change – 20% reduction Climate Change – 10% reduction

  46. When Will Lake Mead Go Dry?Water Resources Research, 2008 • Water Budget Analysis • One 50 maf reservoir, increasing UB demands (13.5 in 2008 ->14.1 maf/yr in 2030, 15.1 maf /yr inflows, current starting contents • Linear Climate Change Reduction in Flows w/ some natural variability • Results With Linear 20% Reduction in mean flows Over 50 years • 10% Chance Live Storage Gone by 2013 • 50% Chance Live Storage Gone by 2021 • 50% Chance Loss of Power by 2017 • Problems • 1.7 maf/year fixed evaporation plus bank storage • Missing 850 kaf/yr inflows • Forgotten / Ignored Issues • System is on a knife-edge, even with existing flows • Normal climate variability can push us over the edge without climate change

  47. Probability of at least one drying – Barnett and Pierce (2008) Yellow – AR-1 (Barnett and Pierce, 2008) Red – Scenario I Green – Scenario II Blue – Scenario II

  48. Probability of drying in a given year

  49. Climate Change – 20% reduction Shortage Statistics Shortage Frequency Shortage Volume (MaF)

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