March 21 2011
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Current CBRFC Water Supply Forecast Methodology. March 21, 2011. Kevin Werner NWS Colorado Basin River Forecast Center. Colorado Basin River Forecast Center. One of 13 River Forecast Centers Established in the 1940s for water supply forecasting Three primary missions:

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March 21 2011

Current CBRFC Water Supply Forecast Methodology

March 21, 2011

Kevin Werner

NWS Colorado Basin River Forecast Center


Colorado basin river forecast center

Colorado Basin River Forecast Center

One of 13 River Forecast Centers

Established in the 1940s 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

www.cbrfc.noaa.gov


Water supply forecasts

Water Supply Forecasts

  • Generated seasonally

  • Typically January through June

  • Updated monthly or as needed

  • Forecast runoff volume (usually April – July)

  • Probabilistic


March 21 2011

Web Reference: www.cbrfc.noaa.gov/gmap/gmapm.php?wcon=checked


Water supply forecast methods

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)

Ensemble 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


Statistical water supply sws

?

Statistical Water Supply (SWS)

  • Equations built on relationships between the inputs and the output

Output Variable:

April-July streamflow volume at Provo-Woodland


Statistical water supply sws1

Source: NRCS

Statistical Water Supply (SWS)

  • Equations built on relationships between the inputs and the output

Input Variable: Trial Lake Snow


Water supply forecast methods1

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)

Ensemble 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


General rfc model

Forecast

precip / temp

General RFC Model

Hydrologic Model Analysis

hydrologic

expertise &

judgment

model

guidance

River

Forecast

System

Weather and Climate Forecasts

River Forecasts

Outputs

Graphics

Analysis &

Quality Control

parameters

Observed

Data

Calibration


Rfc models

RFC Models

  • 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

Snow Model: SNOW-17 Temperature Index Snow model


Calibration

Calibration

  • 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.


March 21 2011

San Juan Basin


March 21 2011

San Juan-Pagosa Springs(PSPC2)


March 21 2011

San Juan-Pagosa Springs(PSPC2)

Upper (11000-12644)

Middle (8500-11000)

Lower (7198-8500)


Weather and climate forecasts

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 process

Forecast

precip / temp

Forecast Process

Hydrologic Model Analysis

hydrologic

expertise &

judgment

model

guidance

River

Forecast

System

Weather and Climate Forecasts

River Forecasts

Outputs

Graphics

Rules, values, other factors, politics

Analysis &

Quality Control

parameters

Observed

Data

Calibration

Decisions


Cbrfc research needs

CBRFC Research Needs

3. Develop reliable ensemble forecast system

4. Improve physical process understanding and modeling

2. Improve use of weather and climate forecasts

1. Improve precipitation analysis

5. Decision Support: Work with stakeholders to use forecasts


Water supply forecast overview

Water Supply Forecast Overview

SWS (Statistical Prediction)

Official Coordinated Forecast

ESP (Hydrologic Model Prediction)

(River Forecast Centers)

VIPER (Statistical Prediction)

Forecast Coordination

(Water and Climate Center)

Other Inputs

.

.

.

.

Decisions

Water Managers and Users


March 21 2011

Statistical 50% exceedance Forecast:

222 kac-ft


March 21 2011

Ensemble 50% exceedance Forecast:

230 kac-ft


Esp applications

ESP applications

  • CBRFC currently provides “raw” ensemble time series forecasts to several groups:

  • Denver Water

  • Pacificorps (Bear River)

  • USBR (Gunnison, Utah, and MTOM)

  • Forecasts updated daily in winter/spring

  • Available via CBRFC webpage


Applications of probabilistic flow forecasts

Applications of Probabilistic Flow Forecasts

  • Denver Water:

  • Long history of using ensemble forecasts for risk management

  • Download CBRFC ensemble forecasts into reservoir operations spreadsheet (right)

  • Optimize reservoir operations by minimizing negative impacts

  • Southern CA MWD:

  • Requested forecast for probability of equalization releases from Lake Powell

  • USBR determines inflow volume required to trigger equalization from 24 month study

  • CBRFC uses regulated ESP forecast to determine probability of reaching the required volume


Forecast coordination

Forecast Coordination

  • Forecasts are coordinated with NRCS on a monthly basis. Forecasters at each agency compare forecasts, analyze differences, and come up with a official, coordinated forecast.

NRCS Preferred Forecast:

235 kac-ft

NOAA Preferred Forecast:

225 kac-ft

Coordinated Forecast:

230 kac-ft


Water supply forecast overview1

Water Supply Forecast Overview

SWS (Statistical Prediction): 222 KAF

Official Coordinated Forecast:

230 KAF

ESP (Hydrologic Model Prediction) : 230 KAF

(River Forecast Centers)

VIPER (Statistical Prediction) : 236 KAF

Forecast Coordination

NOAA: 225 KAF

NRCS: 236 KAF

(Water and Climate Center)

Other Inputs

.

.

.

.

Decisions

Water Managers and Users


March 21 2011

Forecast Verification

Beginning in 2008, CBRFC began verifying all water supply forecasts both for current year and systematically over previous years

Current forecast system has skill

SWS and ESP have somewhat different error characteristics

Skill is typically near zero in Jan/Feb and increases substantially into spring

www.cbrfc.noaa.gov -> Water Supply -> Verification


Discussion

Discussion

  • Unmet stakeholder requirements:

    • Assessment and incorporation of weather and climate forecasts into water supply forecasts

    • Forecast horizon out to two years

    • Objective (and therefore repeatable) forecast system

  • CBRFC is committed to working with partners (you all) to meet these and other requirements

  • Need to move forward in a responsible way that builds on or bridges from current forecast system


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