HyMet Runoff Volume

Forecast Model

October 2010 Presentation | by Wendell Tangborn

HyMet, Inc. | 19001 Vashon Hwy SW Suite # 201 | Vashon, WA 98070 | www.hymet.com

Outline

Introduction

Structure of HyMet Model

Characteristics of HyMet Model

Forecast Examples

Comparisons

Conclusions

Accuracy

Advantages Over other Models

Differences

1

Introduction

Forecasts of

Columbia River inflow

at Grand Coulee,

Lower Granite and

The Dalles are

distributed on a

weekly basis

beginning late

November through

mid-September

for the upcoming

2010-2011 water

year.

3

Runoff Volume Forecasts

4

Importance of Runoff Volume

Importance of Columbia

River runoff volume in

the Pacific Northwest

region:

Hydropower Electricity

Irrigation

Fisheries

Recreation

6

Structure of Model

6

Runoff Model Flow Chart

7

Area Altitude Profile for The Dalles Basin

9

Characteristics of Model

57 Precipitation stations are selected from a list

of 2197 stations located in Montana, Idaho,

Oregon, Wyoming and Washington.

Calibration period of a selected precipitation station

regressed with basin runoff: 1969-85

Verification period of a selected precipitation station

regressed with basin runoff: 1986-2010

Forecast coefficients are first determined in

calibration, then applied in verification for each

precipitation station

9

Selection of Precipitation Stations

Temperature Station10

Weather Stations Used in Model

1. Precipitation Multiplier

2. Precipitation Intercept

3. Fraction of Snowmelt or Rain to Soil

4. Maximum Precipitation Multiplier

5. Ablation from Temperature without Precipitation

6. Ablation from Temperature with Precipitation

7. Ablation from Temperature Range

8. Snowmelt Factor

9. Factor for Soil Moisture ET

10. Factor for Snowpack Sublimation

11. Fraction of Snowmelt or Rain to Groundwater Storage

12. Groundwater Outflow Multiplier

13. Groundwater Outflow Exponent

14. Lower Lapse Rate Threshold

15. Upper Lapse Rate Threshold

11

Model Calibration: 15 Coefficients

R2 = 0.9549

0

20

40

60

80

100

0 5 10 15 20 25

Basin Water Storage (Inches)

Ru

no

ff V

olu

me

(M

AF

)

12

Basin Water Storage vs. Forecast Volume

Grand Coulee Dam April 1, 2009

14

Forecast Examples

Weekly forecasts contain 7

pages

Forecast seasons:

Forecast day- Sep30

January- July

April - July

April - September

January - September

Forecast in MAF

Forecast as % of (1971-

2000)Mean

R-square and Mean Error %

Confidence levels for forecast

Season14

Page 1 – Forecast Overview

Grand Coulee, Lower

Granite and The Dalles

Basins

Daily basin water storage from

beginning of water year to

September 30

15

Page 2 - Water Basin Storage

16

Page 3 - Water Basin Storage

Grand Coulee, Lower Granite

and The Dalles Basins

Distribution of mean basin water

storage with elevation

17

Page 4 - Hydrograph

Grand Coulee, Lower Granite

and The Dalles Basins

Mean (1969-2009)

Actual natural flow condition up

to the forecast day

Actual regulated flow condition

up to forecast day

Forecast hydrograph

18

Page 5 - Hydrograph

Grand Coulee, Lower Granite

and The Dalles Basins

Cumulated runoff volume charts

for each basin

19

Page 6 – Precipitation & Temperature Summary

Average, observed and

deviation of each parameter

for the entire season, and for

previous week

Precipitation (inches)

Temperature (degrees)

Reconstructed Natural Inflows

(MAF)

20

Page 7 - Confidence Levels

Calculated from Forecast and

Error

Example of 90% lower

confidence level for Jan-Jul

forecast:

CL90=Forecast-1.645 *Error

Forecast = 87% (Equal chance

observed runoff will be above or

below 87%)

CL=68% (9 in 10 chance runoff

will be at least 68%

1 in 10 chance observed will be

less than 68%)

22

Comparisons

22

Comparisons of HyMet Forecasts

Comparison Charts of HyMet, RFC and ESP

methods for Jan-Jul and Apr-Sep forecast

seasons

Grand Coulee Basin

The Dalles Basin

Lower Granite Basin

23

Comparisons – Grand Coulee Basin

24

Comparisons – The Dalles Basin

25

Comparisons – Lower Granite Basin

27

Conclusions

27

HyMet forecasts have proven equally, if not more

accurate compared to other forecast methods

Accuracy

HyMet RFC ESP

WY/BASIN GCL LWG TDA GCL LWG TDA GCL LWG TDA

2005 2.8 11.0 4.5 5.8 10.1 7.4

2006 5.8 7.9 5.0 7.0 6.6 6.4

2007 3.9 21.8 5.3 2.0 13.2 4.8 5.4 15.8 8.4

2008 5.6 11.3 7.1 2.9 2.5 2.6 3.2 5.1 3.9

2009 7.3 13.9 3.9 8.1 11.2 2.5 7.8 9.0 4.3

2010 5.0 6.8 4.4 5.9 13.8 9.9 8.3 13.7 10.9

MEAN 5.1 12.1 5.0 5.3 9.6 5.6 6.2 10.9 6.9

28

Advantages

Advantages of HyMet forecasts over others:

Equally, if not more accurate

More informative

Weekly delivery; directly to your email inbox

Longer forecast season

Excel worksheet available for any date in water

year

Distribution to multiple users (5 per subscription)

Differences:

We do not incorporate the future varying weather

conditions in the model and assume normal future

precipitation for the season.

30

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