An Evaluation of NOAA Atlas 14 for Extreme

Rainstorms in Colorado and the United States

Robert D. Jarrett, Ph.D.

Flood and Paleoflood Science, LLC

paleoflood@comcast.net

ALERT Users Group

Ventura, California

October 15, 2020

Presentation Overview• Introduction/Background

• Colorado September 2013 Rainstorm/Flood

• Evaluation of NOAA Atlas 14 in Colorado

• Expanded NOAA Atlas 14 Analysis for the US

• Need to Document Rainstorms and Floods

• Concluding Remarks

• How many use NOAA Atlas 14?

• What is a bucket survey?

• Who has done a bucket survey?

• Are there 10k-yr, 1M-yr rainstorms?

Selected Introductory Questions

• What is the likelihood the maximum rainfall

from a storm will occur at a rain gage?

Corps of Engineers, Buffalo District, New York

1971-1974

Wellsville Hospital

Genesee R at Rochester, NY

“Various Federal and State agencies sometimes make field

surveys after an unusually large storm to collect

‘bucket-survey’ data, which are measurements of rainfall

caught in narrow-bore tubes, buckets, watering troughs,

bottles, and similar containers.” USDA, National Engineering Handbook

Rainfall Bucket Survey

Corps of Engineers, National Weather Service, and

Bureau of Reclamation; they maintain US storm files

Bucket data supplement’s gage data

Total maximum

rain gage data

13.27 inches (348 mm)

in ~60 hrs

Bucket survey

24+ inches

(610+ mm)

Genesee River Basin, NY

US Geological Survey, Denver, Colorado

1974-2012

Colorado state record for 24-hr rainfall = 301 mm

at a precipitation GAGE in

Colorado Springs, Colorado, September 12, 2013

vs

610 mm in about 4 hrs

from a BUCKET SURVEY in

Hale, Colorado, May 31, 1935

Another Gage vs Bucket Survey

Example/Comparison

Flow

(Source: USGS)

A 50-year career of studying extreme storms, floods, & paleofloods

Presentation Overview

• Introduction/Background

• Colorado September 2013 Rainstorm/Flood

• Evaluation of NOAA Atlas 14 in Colorado

• Expanded NOAA Atlas 14 Analysis for the US

• Need to Document Rainstorms and Floods

• Concluding Remarks

Total Sept 2013 Storm Rainfall

Ft Collins

Denver

Dillon

Boulder

Up to 20 inches (508 mm) in 7 days (most in 4 days)

(Source: NOAA)

NOAA-14 2013 Rainfall Frequency Map

At Big Elk Meadows, this was the 2nd 508 mm storm in 4 days in last 50 years!

Reported as

“a 1,000-yr

Storm”

Sept 2013 Flood Damages

Phot credit: UDFCD

Denver

Boulder County

• 9 people died

• $4B in damages

• Most stream gages were

damaged or destroyed before

flood peak

Salina (nr Boulder)Phot credit: UDFCD

Phot creitd: Denver Post

2013 Post-Flood DocumentationFlood and Paleoflood Science, LLC

North Fk Big Thompson R at Drake gage

M Fk St Vrain Cr at Raymond

Dana McGlone

Sponsors:

Data provided 1-3 days after

field visit

NWS gage

(no damage)

made 150 flood estimates at $250/site

September 2013 Flood-Frequency Estimates

Source:

Colorado

Water

Conservation

Board

Max Flood

Recurrence

Interval =

600-700 yrs

Presentation Overview

• Introduction/Background

• Colorado September 2013 Rainstorm/Flood

• Evaluation of NOAA Atlas 14 in Colorado

• Expanded NOAA Atlas 14 Analysis for the US

• Need to Document Rainstorms and Floods

• Concluding Remarks

NOAA Atlas 14

analysis included

16,227 gages

Map of stations recording at 1-day

intervals used in frequency analysis

Recognize extraordinary time & effort

to develop NOAA Atlas 14

https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_cont.html?bkmrk=pa

NOAA Atlas 14 for center of September 2013 Storm

Provides rainfall-frequency-duration estimates

based on analyses of US precipitation GAGE data

NOAA Atlas 14 for Center of September 2013 Storm

= 2.36 in

Two storm of 508 mm/4days (1969 & 2013) had RIs ~ 30,000 yrs

Big Elk Meadows, Colorado, September 2013

RI= 10k yrs RI= 1M yrs

Big Elk Meadows, Colorado, September 2013

Uncertainty/range of AEP.

Analysis of Extreme Rainfall data in Colorado

Precipitation

gage data

and

Miscellaneous

site data

(bucket survey)

Data available from pre-1900 to 1997

Study Area: Eastern Colorado(100 point rainfall observations)

The study area is relatively hydrologically homogeneous

July 31, 1976 Record Storm/Flood

X 7/31/1976

NOAA Atlas 14

1. RF Data from Mckee & Doesken (1997) & 2013 Data

2. Mostly rainfall buckey survey data, which was

not used to develop NOAA Atlas 14.

NOAA Atlas 14

Are these results reasonable or implausible?

100

Presentation Overview

• Introduction/Background

• Colorado September 2013 Rainstorm/Flood

• Evaluation of NOAA Atlas 14 in Colorado

• Expanded NOAA Atlas 14 Analysis for the US

• Need to Document Rainstorms and Floods

• Concluding Remarks

Harvey is worst rainstorm in US historyA 1,000-year rainstorm in Houston, Tx, 1,321 mm in four

days” August 2017

In July 1979, T.S. Claudette produced 1,092 mm of rain in

24 hours in Houston (RI>1,000 yr) – currently the

continental US record for 24-hour storm duration

USA Today May 29, 2018

Real/Coincidence?, Evidence of Global Warming?, NOAA14 issue?

Extreme

rainstorms in

2016 & 2018

Sources of US Rainfall data (81 sites) in the of

extreme rainfall data in the United States(a sub-set of a much larger extreme rainfall data)

DATA SOURCES

Bullard, K.R., 1986, Comparison of estimated maximum flood peaks with

historic floods: U.S. Department of the Interior, Bureau of Reclamation, Denver,

CO, 165 p.

O’Connor, J.E. and Costa, J.E, 2004, Spatial distribution of the largest rainfall-

runoff floods from basins between 2.6 and 26,000 km2 in the United States and

Puerto Rico: Water Resources Research, V. 40, W01107, 11 p.

NOAA’S greatest observed point precipitation values for the United Stateshttps://www.nws.noaa.gov/oh/hdsc/record_precip/record_precip_us.html

X 925 mm/18-hr

NOAA Atlas 14

Storm of September 9, 1921

Thrall, Texas

X 871 mm/12-hr

NOAA Atlas 14

Storm of July 17, 1942

Smethport, Pennsylvania

100

US Record Rainfall Data(USBR, O’Connor & Costa, NOAA data)

Are these results plausible?

Overarching Theme

NOAA Atlas 14 has a substantial bias to

underestimate rainfall amounts for a

given frequency?

Proposed Future Study Title

“Precipitation-frequency relations based on gaged

and regional maxima data for the United States”

Presentation Overview

• Introduction/Background

• Colorado September 2013 Rainstorm/Flood

• Evaluation of NOAA Atlas 14 in Colorado

• Expanded NOAA Atlas 14 Analysis for the US

• Need to Document Rainstorms and Floods

• Concluding Remarks

Houses for sale

Denver, Colorado

“A modeling approach does not decrease the

amount of data required; in fact, it increases it.

Modeling is not a replacement for observation.”

National Research Council (1992)

Q

Concluding Thoughts

• NOAA 14 probably underestimates from about

AEP ≤0.02 or (RIs ≥ 50+ years)

• Is there a need to alert NOAA14 users of issue?

• There is a need to increase the documentation of

rainstorms and floods; systematic documentation

substantially decreased about the 1980s

• Incorporating extreme RF data from bucket surveys

(CoCoRAHS, radar, etc.) is essential for reliable

rainfall-frequency estimates

• Acknowledgement: John England, Jr., (USACE);

provided rainfall data in digital format

Relation between flood and paleoflood peak discharge and drainage

area with flood-frequency curves for northwestern Colorado

A final thought: Do floods exhibit a similar issue as extreme

rainfall datawhen miscellaneous site flood and paleoflood data

are included? No.