Managing Climate Risks on the Colorado River
Balaji Rajagopalan Department of Civil, Environmental and
Architectural Engineering & CIRES University of Colorado, Boulder, CO
Symposium on Climate Risk Management Oct 10-12, 2011
Guayaquil, Ecuador
Acknowledgments
•Kevin Werner & Andy Wood – CBRFC, NOAA/NWS, Salt Lake City, UT
•Cameron Bracken, University of Colorado, Boulder, CO
•Kenneth Nowak, University of Colorado, Boulder, CO & USBR
•Katrina Grantz – USBR, Salt Lake City, UT
•Seasonal to Year-Two Colorado River Streamflow Prediction Workshop, Mar 21-22, 2011, Salt Lake City, UT
• http://www.cbrfc.noaa.gov/present/2011/s1y2/agenda.htm
Colorado River Basin Overview n 7 States, 2 Nations
n Upper Basin: CO, UT, WY, NM n Lower Basin: AZ, CA, NV
n Fastest Growing Part of the U.S. n Over 1,450 miles in length n Basin makes up about 8% of total
U.S. lands n Highly variable Natural Flow
which averages 15 MAF n 60 MAF of total storage
n 4x Annual Flow n 50 MAF in Powell + Mead
n Irrigates 3.5 million acres n Serves 30 million people n Very Complicated Legal
Environment ‘Law of the River‛ n Denver, Albuquerque, Phoenix,
Tucson, Las Vegas, Los Angeles, San Diego all use CRB water
n DOI Reclamation Operates Mead/Powell 1 acre-foot = 325,000 gals, 1 maf = 325 * 10 9 gals
1 maf = 1.23 km 3 = 1.23*10 9 m 3
Motivation Recent conditions in the
Paleo Context n Below normal flows into
Lake Powell 2000-2004 n 62%, 59%, 25%, 51%, 51%,
respectively n 2002 at 25% lowest
inflow recorded since completion of Glen Canyon Dam
n Some relief in 2005 n 105% of normal inflows
n Not in 2006 ! n 73% of normal inflows
n 2007 at 68% of Normal inflows
n 2008 at 111% of Normal inflows
n 2009 at 88% and 2010 at 72.5%
n Decadal Variability! 5 year running average Woodhouse et al., WRR, 2007
Needs
nGiven the stress on the system (socio-economic & climate via droughts) skillful long-lead streamflow forecasts on the Colorado River Basin are crucial for efficient system management.
nForecasts of spring (Apr-Jul) flow, the key inflow period are desired at lead times starting previous November at each month.
nForecasts are required at a number of ‘decision point‛ locations on the River Basin.
nNeed to Manage Climate Risk at short (seasonal to interannual) and long (multidecadal) time scales
Water Supply Forecast Overview
SWS (Statistical Prediction) ESP (Hydrologic Model Prediction)
(River Forecast Centers)
VIPER (Statistical Prediction)
(Water and Climate Center)
Forecast Coordination
Official Coordinate d Forecast
Water Managers and Users
Other Inputs . . . .
Decisions
Water Supply Forecast Methods Statistical Forecasting
§ Statistical Regression Equations
§ Primary NOAA/RFC forecast method from 1940‛s to mid 1990‛s.
§ Primary NRCS/NWCC forecast method
§ Historical Relationships between flow, snow, & precipitation (1971- 2000+)
§ Tied to a fixed runoff period (inflexible)
ØEnsemble Simulation Model Forecasting
§ A component of a continuous conceptual model (NWSRFS)
§ Continuous real time inputs (temperature, precipitation, forecasts)
§ Accounts for soil moisture states (SAC-SMA) - drives runoff efficiency
§ Builds and melts snowpack (Snow-17) – output feeds SAC-SMA
§ Flexible run date, forecast period, forecast parameters.
§ Evolving toward ESP as primary forecast tool at NOAA/RFCs
13 River Forecast Centers
Established in the 1940s around major river basins for water supply forecasting
Three primary missions:
1. Seasonal Water supply forecasts for water management
2. Daily forecasts for flood, recreation, water management
3. Flash flood warning support
4. Each RFC develops hydrologic models relevant for their basin/region
They integrate short term and seasonal
Forecasts from NWS/NOAA
Colorado Basin River Forecasting Center Example
www.cbrfc.noaa.gov
River Forecast Centers
Weather and Climate Forecasts
RFC forecast system incorporates both weather and climate forecasts:
• Weather forecasts integrated into daily operations with forecaster control over point and basin average values • Water supply forecasts
typically only use QPF during late season or in lower basin
• When QPF is used, it is used in a deterministic manner
• Climate forecasts integrated into seasonal water supply forecasts through probability shifts of forcing ensemble • Climate forecasts are
typically only considered in lower basin and only in ENSO years
Forecast precip / temp
General RFC Model
Weather and Clim
ate Fo
recasts
River Forecast System
parameters
Observed Data
Analysis & Quality Control
Calibration
model guidance
Hydrologic Model Analysis
hydrologic expertise & judgment
Outputs Graphics
River Forecasts Forecast
precip / temp
Weather and Clim
ate Fo
recasts
River Forecast System
Observed Data
Calibration
model guidance
Hydrologic Model Analysis
hydrologic expertise & judgment
Outputs Graphics
River Forecasts
Snow Model: SNOW-17 Temperature Index Snow model
RFC forecast uses a snow model and a rainfall-runoff model:
• SNOW-17: Temperature index model for simulating snowpack accumulation and melt
• Sacramento Soil Moisture Accounting Model: Conceptual hydrologic model used to generate runoff
RFC Models
• River basin is divided into ‘homogeneous‛ sub-basins based on topographical attributes (using GIS, Remote-sensing data etc.)
• For each sub-basin historic 6-hour weather (Precip., Tmax, Tmin) are developed for three ‘regions‛ – higher, middle and lower elevations. • All historic data is
used in this process. • Natural / unregulated
streamflow data is also compiled
• The Hydrologic model is calibrated
• These are constantly updated
Key Steps in Model Building
Key Steps in Model Building
• Process to assign parameter values to the runoff and snow modules within the model. Unique set for each basin (and sub-basin)
• Quality of calibration can vary greatly from basin to basin depending on data availability, period or record, quality of data, hydrology of the basin, etc.
• Archiving and Maintaining Data *Very Important*
Ensemble Streamflow Prediction
ESP applications CBRFC currently provides
“raw” ensemble time series forecasts to several user groups:
• Denver Water Utility • Pacificorps (Bear River,
UT) • USBR (Gunnison, Utah,
and MTOM) Forecasts updated daily in
winter/spring Available via CBRFC
webpage http://www.cbrfc.noaa.gov/ à
Hydrodata 15
Web Reference: www.cbrfc.noaa.gov/gmap/gmapm.php?wcon=checked
Dissemination / Verification • The forecasts are
disseminated online • Ensembles provided as
raw data http://www.cbrfc.noaa.gov
/ à Hydrodata • Very good visualization
tools showing a suite of forecast and observed variables.
http://www.cbrfc.noaa.gov / à (links on the left column)
• Forecast Verification • http://www.cbrfc.noaa.
gov/ à (Verification)
CBRFC Products
n RFCs (CBRFC in particular) are a source of wealth of information for hydrology and water supply. They provide current, forecast and historic information. n Western US wide – all aspects of water supply
n Water Supply Outlook
n Current Snow Conditions
n 0-14 day Outlook
n Reservoir Outlook
n NRCS - products
La Nina Winter 2011
El Nina Winter 2010
Snowpack Maps / Data NRCS
Proposed Improvements
n Newer statistical models for multi-side ensemble streamflow forecasting are being tested and developed for integration with the CBRFC forecasting system (e.g., Bracken et al., 2011, Regonda et al., 2006)
§ Using large-scale climate information with multi-model statistical ensemble forecasting techniques
n Current ESP limited (by the length of the historical data) in its ability to generate ensembles
§ Stochastic weather generators can provide a rich variety of input daily weather ensembles
§ Easy to condition them on probabilistic seasonal forecast
(e.g., Apipattanavis, et al., 2007; Apipattanavis, 2008)
n Optimal combination of statistical and watershed model based forecasts
Bracken et al. 2010, WRR
Using Climate Information for longlead Streamflow Forecast
Water Resources Management (Interannual time scale)
n Reservoir Operations n 12 major reservoirs (9
Upper, 3 Lower Basin) n Seasonal/Monthly forecasts
are input to the ‘systems‛ model n In RiverWare – contains
all the operating rules and constraints
n Obtain mid-term reservoir conditions (storage, elevation, release, hydropower, etc.)
n Close coordination between USBR and CBRFC
Western Water Western Water Assessment Assessment
Seasonal to Two Year Simulation and Forecasting • Hidden Markov model for simulation and forecasting
HMM Forecast
Seasonal Forecast Historical Data
Midterm Operations Model
Probabilistic Reservoir Outlook
1000 32 Mo. Traces
0 5 10 15 20 25 30
3540
3560
3580
3600
3620
3640
3660
Month
Pool Elevation [feet]
Water Resources Data/Information
n USBR archives and disseminates historical streamflow and reservoir data; current status; operating plans; real time releases etc. n The stakeholders and general public can get a very good idea of the
state of the resources
n Current Reservoir Levels
n Current snowpack in the sub-basins
n Operating Plans, Historic Data
n Current Reservoir Status
Western Water Western Water Assessment Assessment
Decadal Scale Stochastic Streamflow Simulation and Water Resources Management
• Analysis of natural and paleo flow variability – Identify spatially persistent modes of flow variability
• Wavelet spectral methods and principal component analysis
– Identify potential climatic drivers of variability • Spectral coherence with climate indices; correlation with climate variables
– Develop simulation methods that reflect variance analysis • Capture historic/simulate future spectrum; condition on climate projection
• Colorado River Water Resources Management – Analysis of CRSS model to identify system components sensitive to certain flow or variance regimes
– Develop adaptive management policies to demonstrate improved system outcomes associated with variability understanding
Western Water Western Water Assessment Assessment
Wavelet Power Spectrum of Lees Ferry Flow Features of interest 1) decadal (active past 30 years) 2) Low frequency (more persistent)
UCRB PRISM Temperature Spectrum
UCRB PRISM Precipitation Spectrum
•Raw WY flow and precipitation correlation = 0.77
•Raw WY flow and WY temperature correlation = 0.32
Western Water Western Water Assessment Assessment
Decadal Flow Projection
• Given persistent low frequency variability (natural flow and paleo data) mode, what can previous conditions inform about future characteristics?
?
• Application to 2 periods of paleo data
Below, 1634 to 1683 20 year mean flow projections
Right, 1925 to 1974 20 year mean flow projections
Thoughts/Ideas for Transfer to Other Context § RFC structure should be seriously considered for Hydrologic
Forecast § Effective interface with weather/climate forecasts
n Data collection / management
§ Robust collection and archiving of meteorologic and, hydrologic data in particular, is critical for skillful forecasts
§ Resources from Met services, and State agencies can be pooled
§ Close coordination and collaboration with Water Management and state holders in the basin
§ Effective outreach – online dissemination, weekly/monthly outlook briefings, workshops
§ Model Development/Improvement
§ This is always an on-going process. The forecasting framework need to be constantly improved, calibrated and validated.
§ Need to have a good capacity and human resources building strategy
