Models and Calibration

CBRFC 2011 Stakeholder Forum

November 3, 2011

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CBRFC Forecast Groups

White Yampa

White Yampa Basin

ENMC2

White Yampa - Elk near Milner (ENMC2)

Upper (10000-11970)

Middle (8500-10000)

Lower (7205-8500)

White Yampa - Elk near Milner (ENMC2)

In reality the 3 areas (upper, middle and lower) are represented (simulated) by only 3 points (Lumped Model)

The inputs our model needs for calibrations and operations (at these 3 points) are:• precipitation• temperature• freezing level

Calibrations/Simulations - inputs

ENMC2 upper areaElevation = 10569 ftArea = 64 sqmi

ENMC2 middle areaElevation = 9146 ftArea =159 sqmi

ENMC2 lower areaElevation = 7692 ftArea =246 sqmi

For Elk River at Milner (ENMC2)

Each area (upper, middle and lower) MAP is built using precipitation stations that (hopefully) have similar characteristics to that area

For the ENMC2• Upper area – DRLC2 .46, ELKC2.46• Middle area - DRLC2 .46, ELKC2.46• Lower area - DRLC2 .46, ELKC2.46

These weights were chosen to guarantee water balance in each area. The water balance in each area was calculated using the PRISM sets

Calibrations/Simulations - Precipitation

White Yampa - Elk near Milner (ENMC2)Precipitation Gages

Nearby stations (whose climatology is known) area used to calculate the temperature at the mid-point elevation of the area (whose climatologies are calculated using the climatology of the nearby stations)

Temperature is calculated by using the difference in station and area climatology

For the ENMC2• Upper area – CRSC2 0.009, ELKC2 0.011• Middle area - SBTC2 0.009, CRSC2 0.013, ELKC2

0.045• Lower area - WBSW4 0.009, SBTC2 .02,HAYC2

0.013, ELKC2 0.019

Calibrations/Simulations - Temperature

White Yampa - Elk near Milner (ENMC2)Temperature Gages

Precipitation and temperature are calculated every six hours at each area within the basin

30 year historical record calculation• Used to calibrate hydrologic models Operationally done in a similar way• Ensures our forecasts will have similar

quality/characteristics to calibration For the Elk at Milner this is done for the upper,

middle and lower areas

Calibrations/Simulations - Inputs

A snow model is first run for each area in the basin• accumulates/ablates snow A soil moisture model is then run for each area• Controls amount of water from the snow model • retained in the soil• evaporates or• ends up in the stream Evaporation is a calibrated amount:• E=P-Q

Calibrations/Simulations - Models

SNOW ACCUMULATIONAND ABLATION MODEL (SNOW-

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Precipitationand

Air Temperature

Rainor

Snow

Energy Exchangeat

Snow-AirInterface

Snow CoverHeat Deficit

GroundMelt

SnowCover

OutflowRain plusMelt

Areal Extentof the

Snow Cover

Liquid WaterStorage

Transmissionof

Excess Water

AccumulatedSnow Cover

Rainon

Bare Ground

Deficit = 0

Bare ground or

snow cover

Sacramento Soil MoistureAccounting Model

TENSION WATER STORAGE

FREE WATER STORAGE

PRIMARYFREE

WATERSTORAGE

TENSIONWATER

STORAGE

TENSIONWATER

STORAGE

SUPPLEMENTARYFREE WATER

STORAGE

LOWER ZONE

UPPER ZONEDIRECTRUNOFF

INTERFLOW

SURFACERUNOFF

BASEFLOW

SUBSURFACEOUTFLOW

Calibrations - Results

Simulations - Real Time (no mods)

Simulations - Results (with mods)

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Reservoir modeling is difficult as they are not physically based. However, we calibrate the reservoir models assuming two different modes:• Irrigation (use average releases)• Spillway/passflow

Operationally we can do the following:• Assume the current release • Input a schedule• Allow the spill/passflow rules

Calibrations/Simulations - Reservoirs

Reservoir Calibrations

Reservoir Simulations – Assume Constant Outflow

Reservoir Simulations – Use Rules

Reservoir Simulations – Use Rules

Reservoir Simulations – Release Schedule

Unregulated flow = Observed flow + Diversions (measured) + Storage

Natural flow = Unregulated flow + Consumptive Use Consumptive use (in basin irrigation) can only be estimated• In our simulations, we simulate natural flow but subtract

out the consumptive use so the output is always unregulated flow

So:• We simulate “natural flow”• We remove the in-basin irrigation (consumptive use)• This is the simulated unregulated flow. It simulates the

actual flow plus the measured diversions (adjusted flow) Operational considerations• Observed flow = Unregulated flow - Diversions - Storage

Adjustments to Flow

http://www.cbrfc.noaa.gov/wsup/doc.php

463 basins• 1139 sub areas (1-3 per basin)

88 reservoirs 22 routes (no snow model or soil model)

Calibrations/Simulations

30 year averages are updated once every 10 years

WY2011 Used:• 1971-2000 for averages• 1971-2000 for statistical prediction• 1976-2005 for ESP

Update for WY2012 will be based on 1981-2010 time series• New averages based on 1981-2010• New statistical prediction equations based on 1981-2010

period• Recalibration of 463 river basin models to the 1981-2010

period• Better effort made to create MAP and MAT time series• CBRFC will debut all of this for January 2012 forecasts

Recalibration

• Preliminary Data• 18% reduction in

mean

Effect on Forecasts

WY2012 forecasts will be based on 1981-2010 inputs in both forecast models• ESP and SWS will both use the same period

SNOTEL network much stronger for 1981-2010 period than in 1970s. This network is critical for forecast skill.

All things equal, these forecasts will be lower since input data sets are drier in the 30 year average• Especially true in early season forecasts• Later season forecasts more controlled by observed

snowpack

Percent of normal forecast values should remain largely unchanged (since normals AND forecasts will be lower)

Example: ESP forecastsMean influence to early season forecasts somewhat less

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Example: ESP forecastsMean influence to late season forecasts small

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Questions

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