Advantages of using Gauge-Adjusted Radar Rainfall During ... · •Saving lives and property – Flash floods, dam failures •Engineering •Hydrologic modeling •Stormwater management

© 1992-2014 OneRain Incorporated

Advantages of using GARR During Extreme Rain Events

Charles Yost Meteorologist – Rainfall Analyst

Importance of Understanding Rainfall

• Saving lives and property – Flash floods, dam failures

• Engineering • Hydrologic modeling • Stormwater management

Outline

Advantages of using Gauge-Adjusted Radar Rainfall (GARR)

during Extreme Rain Events

• What is Gauge-Adjusted Radar Rainfall? • Why adjust it? • What are some advantages of using it during extreme events?

– Evaluation of the validity of rain gauge reports – Understanding rainfall patterns in non-gauged areas – Basin average intensities

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Extreme Rain Event Example

2013 Colorado Flood event • 9 fatalities • 14 counties declared States of Emergencies

– 19+ counties impacted

• $2 - $3 Billion in damages

Extreme Rain Event Example

2013 Colorado Flood event • Roughly 9/9/2013 to 9/15/2013 • Over 191 gauges between UDFCD and Boulder County • Foothills west of urban corridor • Some antecedent conditions • Rain after the event

Rain “ingredients” present for long time…

Reminder: Ingredients for Rain

1. Moisture

2. Lift

3. Instability

1. Moisture

• Tropical-Like in nature • Extremely moist atmosphere • More moisture than 99.9% of

days in CO

2. Lift

Courtesy: EIU

• This is what triggers the rain • Thus, WHERE the rain will

occur • Upslope flow (pic) • Mountains don’t move…so • Localize enhancement

1.

2.

3. Instability

Overview of Storm Sept 9, 2013

• Upper Low over Las Vegas pumping S/SW moisture

• Storms start forming that afternoon

• 9 pm LST cold front moves down

Boulder County

Larimer County

Denver County


• Upper Low remains over SW US

• Feature moves north along foothills

• Second following behind it Boulder

County

Larimer County

Denver County


• Low still north of Las Vegas

• Wave headed north from New Mexico into CO

• Several disturbances move through NE CO

Boulder County

Larimer County

Denver County


• Low still north of Las Vegas

• Low-level moisture

Boulder County

Larimer County

Denver County


• Low moving into WY • Winds almost westerly

means less moisture • Rains continue through

most of Friday • Low ejects out

Saturday

Boulder County

Larimer County

Denver County

Overview of Storm

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Gauge-Adjusted Radar Rainfall

• Over 140 radars throughout country

• Send and receive pulses • Just like detecting planes,

can detect rain • But…

COMET Program - UCAR


COMET Program - UCAR

• Radar detects amount of water

• Does NOT detect rain directly

• Can convert to rain rate using: Z = aRb

• Still issues


• GAUGES: accurate measurements at point locations

• RADAR: coverage between gauges • Calibrate using co-location of point

measurement and radar value • Combining these data sources gives us the

best rainfall estimate available

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GARR Usages: Adjustment

• Use default conversion to rainfall rate • Colorado isn’t perfect

– Mountains, virga, ground clutter • This storm was tropical-like (moisture) in

nature – Different conversion – Don’t know until you’re in the event


Adjusted GARR Raw Radar Difference _ = (Standard Conversion)

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GARR Usage: Evaluate Reports

Using Gauge-Adjusted Radar Rainfall to evaluate the validity of missed gauge reports


0

0.2

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0.8

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1.6

20:00 20:15 20:30 20:45 21:00 21:15 21:30 21:45 22:00 22:15 22:30 22:45 23:00

Surrounding Gauges + Sunset

Logan Mill

Gold Hill

Sunset

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20:00 20:15 20:30 20:45 21:00 21:15 21:30 21:45 22:00 22:15 22:30 22:45 23:00

Surrounding Gauges

Logan Mill

Gold Hill

GARR


GARR pixel value over gauge


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0.8

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1.2

20:00 20:15 20:30 20:45 21:00 21:15 21:30 21:45 22:00 22:15 22:30 22:45 23:00

Sunset Gauge

Without Report

With Report

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1

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20:00 20:15 20:30 20:45 21:00 21:15 21:30 21:45 22:00 22:15 22:30 22:45 23:00

Sunset Gauge

Without Report

With Report

GARR


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1

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20:00 20:15 20:30 20:45 21:00 21:15 21:30 21:45 22:00 22:15 22:30 22:45 23:00

Rain Gauge with GARR

Sunset no report

Sunset with report

Sunset+Garr

Insert GARR for this range

GARR Usages: Evaluate Reports

0

0.2

0.4

0.6

0.8

1

1.2

20:00 20:15 20:30 20:45 21:00 21:15 21:30 21:45 22:00 22:15 22:30 22:45 23:00

Rain Gauge with GARR

Sunset no report

Sunset with report

Sunset+Garr

• Using Basin Average over Four Mile Canyon or pixel value over gauges

• Assess failed validation against: – Volume during that time – Basin-average volume

GARR Usage: Understanding Rainfall

• UDFCD and Boulder County have extensive rain gauge networks

• Still impossible to estimate rainfall over every point

• Hard to interpolate point measurements to spatial info

GARR Usages: Understanding Rainfall

15.75 in

13.12 in

17.69 in

17-18 in

GARR Usage: Basin Intensities

• Historical radar can provide context

• Compare this event to all past September storms

Conclusions

• The Colorado September 2013 flood event was a large and devastating event

• High rainfall rates for over 5 days • Radar alone did a poor job at best • Gauges alone had missing data • GARR is the best representation of rainfall

during an extreme event like this

© 1992-2014 OneRain Incorporated

Thank you!

Questions?


Adjusted GARR Raw Radar Difference _ = (Tropical Conversion)

Documents

Advantages of using Gauge-Adjusted Radar Rainfall During ... · •Saving lives and property – Flash floods, dam failures •Engineering •Hydrologic modeling •Stormwater management