Session 3 Probable Maximum

Precipitation (PMP) Study for Texas

PMP Study

• Started August 2014 • Completion August 2016 • Contractor – Applied Weather Associates • Peer Review Committee

PMP Study Peer Reviewers

• Dr. William Asquith, USGS and Texas Tech

• Dr. John Nielsen-Gammon, State

Climatologist and Texas A&M

• George Bomar, Texas Department of Licensing and Regulation and author of Texas Weather

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PMP Study Peer Reviewers

• Todd Marek, P. E., NRCS, Temple • Simeon Benson, USCOE, Fort Worth • Charles McWilliams, USCOE, Omaha,

Neb. • Debra Rankin, P. E., Retired TCEQ Dam

Safety • Warren Samuelson, P. E., TCEQ Dam

Safety

Contractor Team Applied Weather Associates, LLC

Project Manager and Chief Meteorologist – Bill Kappel

Senior Hydrometeorologist – Doug Hultstrand

Senior GIS Specialist/Staff Scientist – Geoff Muhlestein

Staff Meteorologists – Dana McGlone, Kristi Steinhilber, Bryon

Lawrence, Steve Lovisone, Patrice Sutter

(PMP)Definition: The theoretically greatest depth of precipitation for a given duration that is physically possible over a given storm area at a particular geographic location at a certain time of year (HMR 59, 1999)

Probable Maximum Precipitation

Types of PMP studies: Generalized (Hydrometeorological Reports) Provides PMP values for a region HMR 51 - East of the 105th Meridian from Canada to Mexico

Regional/Statewide Provide PMP values over regions with varying topography Individual basins are included in the regional/statewide

results Site-Specific Provides PMP values for individual drainage basins Considers unique meteorology and topography

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Coverage of HMRs

How Do PMP Studies Provide Improved PMP Values?

• More storms considered • New technologies used • Problems/Unknowns in the HMRs

corrected • Topographic features addressed • Updated climatologies used

Method for Computing PMP Values

• Observed extreme rainfall events are used • Storm based approach

• Identify extreme storms in Texas and regions that are considered transpositionable • Identify recent extreme storms since publication of the

appropriate HMRs • Review older rainfall data records

• Identify extreme storm types • Local storms (thunderstorms/Mesoscale Convective Systems

(MCS)) • General storms (frontal systems) • Hurricanes/Tropical Systems

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Method for Computing PMP Values

• Identify unique topography • Precipitation enhancement/decrease

• Orographic effect • Review HMR/Hydro/Tech Memo procedures

• Identify inconsistent assumptions • Apply new technologies and data • Apply new/updated methods

PMP Study for Texas Project Overview

• Comprehensive evaluations of extreme rainfall storm events

• Extreme rainfall storm identification • Storm analyses • Storm maximization • Storm transpositioning

•Synoptic extreme rainfall (General Storms/ Tropical Storms) •Thunderstorms and Mesoscale Convective System (MCS)

PMP Study for Texas Background

•PMP values as provided in HMRs are overdue for updating

• Storm data base grossly out of date (1970s) • Procedures used to analyze storms outdated • PMP values generally unreasonably

conservatism •Provide greater confidence, credibility, and more accurate/reliable values •Apply updated meteorological understanding and techniques

PMP Study for Texas Procedure

•Update the storm database • Produce Depth-Area-Duration (DAD) analyses for all

major storm events •Use updated dew point/sea surface temperatures to maximize storms

• Storm representative & maximum dew points/SSTs •Use of state-of-the-science procedures and tools

• GIS & Geographic Transposition Factor •Provide PMP values for all locations within Texas

• All locations considered in this study • All durations and area sizes as required

•Utilize GIS to produce PMP on a gridded basis

PMP Study for Texas Procedure

•Follow the basic procedures used in previous AWA studies • Nebraska, Arizona, Ohio, Wyoming statewide PMP

studies • Numerous individual basin PMP studies (Tarrant Regional

Water District) • Michigan and Wisconsin, Texas regional PMP

•Incorporated storms through May 2016 •Used GIS to provide efficient and effective distributions of PMP values across the Texas •PMP to provide continuity of PMP values across the region in

space and time while taking into considerations differences in topography and climate

Issues to Consider • Storm Search Processes

– Direct tropical system landfall limits – Seasonality of storm types – PMP storm type-General-Tropical-Local

• Orographic vs Non-orographic – Balcones Escarpment – Basin and Range of West Texas

• Large size and complexity – Subtle changes from east to west and north to south

• Transposition limits – Similarity of meteorology, topography – Different parameters depending on

• Storm type, moisture source, intervening barriers • Proximity to the coast

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PMP Study for Texas

Task 1 Review of previous studies for applicability 1. AWA PMP studies (e.g Nebraska, Ohio, Arizona,

Wyoming, Tarrant, Arkansas Nuclear One, Quad Cities, etc)

2. HMRs 33, 51, 52, 53, etc 3. USACE and USGS storm and flood analyses

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PMP Study for Texas Task 2

Storm Search and Short List Development • Complete a storm search to identify the most significant

storms that could have occurred over the region where storms are transpositionable to Texas

• Identify storms used in HMRs and other PMP studies • Identify the most significant flood events that have

occurred in region • Identify extreme rainfall-producing storm types and

seasons associated with those storms • Use the Storm Precipitation Analyses System (SPAS) to

analyze extreme rainfall events that have not previously been analyzed

• Use SPAS to reanalyze extreme rainfall events

Intermediate Storm List-All

Storms

Storms used for PMP

Development

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PMP Study for Texas

Task 3 SPAS Storm Analysis • All storms used for PMP develop analyzed with

SPAS • SPAS produces gridded rainfall analysis and

required data sets • USACE storms will need to be re-analyzed

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PMP Study for Texas Task 4

Storm Maximizations/Transpositioning •Utilize the updated maximum dew point climatology for use in storm maximization and transpositioning •Maximum average dew point values

- 6-hour - 12-hour - 24-hour

•Sea Surface Temperatures (SST) climatology for some events

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PMP Study for Texas Task 5

Orographics and Grid Domain Analysis •Develop total adjustment factors on a gridded basis

• 2.5-square miles • Utilize storm Depth-Area-Duration data • Each storm explicitly transpositioned to each grid as

appropriate • Allows for differences across state to be quantified • Each adjustment known and reproducible

Probable Maximum Precipitation Study for Texas

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PMP Study for Texas Task 6

Develop PMP •Values will be provided on a gridded basis or other format •Appropriate durations, 1-hr, 6-hr….as needed

– Not confined to 72-hrs – ~2.5mi2

•Analyze the orographic effects of elevated terrain •Transposition limits for each storm will be determined

- Use the procedures developed in previous PMP studies - Precip frequency data to calculate the Geographic

Transposition Factor - Corrects stippled region in HMR 51/52

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PMP Study for Texas Task 7

Storm Based Hydrology Application •Work with users to provide PMP rainfall information as needed •Updated temporal distributions •Other rainfall characteristics

PMP Study for Texas

Task 8 Quality Control and Sensitivity - Compare results

- HMR PMP values - Precip frequency data - Other PMP studies

- Discuss sensitivity of various parameters and assumptions on the final PMP values

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PMP Study for Texas Task 9

Final Report • A Draft final report will be submitted for review by

the Peer Review Committee • Review comments will be incorporated into a

comprehensive final report as appropriate • An appendix will be provided with all storm details

and calculations used to determine the PMP values throughout Texas

• Maps of PMP values will be provided both in the report as well as in GIS format

PMP Study for Texas Task 10

Review Meetings • Meetings will be held with the peer Review committee to present and review the approach and procedures to be used as well as work completed • Four have been held to date •Additional data has been provided by the committee members

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PMP Study for Texas

Task 11 Updated Precip Frequency

• Build from extensive previous work • Dr. William Asquith’s publications • Southern Regional Climate Center

• Follow same methodology as NOAA Atlas 14 • 6hr and 24hr data used for PMP calculations

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NOAA Atlas 14 Precip Frequency Coverage

Probable Maximum Precipitation Study for Texas

Results •Updated PMP values for all locations

• By storm type • Local, general, tropical • All area sizes and durations from 1-hr through 72

hours • Applied most current storm data and

meteorological analyses •Updated, gridded precipitation frequency climatology for entire region

• 6- and 24-hour thru 1000-yr ARI

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35"N

34'N

33"N

26'N

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110'W 109"W ,oe·w IO)"W

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Precipitation Frequency Map

Tropical Stonn 24-hour PMP (inches)

McMicken Dam Basin

112°37'30"W 112'30W 112"22"30"\'V

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8.22 8.24

8.07 8.09 8.04 7.96 7.91 7.89

7.88 7.89 7.78 7.88 7.61 7.57

7.73 7.74 7.62 7.46 7.33 7.21

7.69 7.65 7.55 7.32 7.09 6.92

7.63 7.49 7.23

7.69 7.51 7.18

24-hr PMP (inches)

. 6.27-6.5

- 6.501 · 6.75

fi!J] 6.751 · 7 O 7.001 . 7.25 0 7.251-7.5

- 7.501 · 7.75

0 7.751-8

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. 8.751-9

D s.001 . 9.25 LJ 9.251-9.5

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33'3T30"N 33'3T30"N

112"3730"'W 112'30'W 11i·=

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What is next

• Prepare final report for per review team to review and provide final comments to TCEQ.

• TCEQ to develop method for making report and GIS grids available

When will it be available

• The report will be online first • The maps will be available later • TCEQ will maintain the data

Product • You must have GIS capabilities • Our initial plan is that you will submit a

polygon of the drainage area • We will provide the precipitation data for the

drainage area.

Proposed date available

• We plan to have everything working by Jan. 1, sooner if possible.

• We will make it known when it is finally available and working

Grace Period

• We will allow at least 6 months from the date the system is working (July 1 if the date is Jan. 1) to use the new PMP

• We do not plan to change the temporal distribution at this time.

Dam Safety Section

TCEQ

MC-177 P. O. Box 13087

Austin, Texas 78711 warren.samuelson@tceq.texas.gov

(512/239-5195) johnny.cosgrove@tceq.texas.gov

(512/239-4307)

mailto:johnny.cosgrove@tceq.texas.govmailto:warren.samuelson@tceq.texas.gov

Questions

Session 3�Probable Maximum Precipitation (PMP) Study for TexasPMP StudyPMP Study Peer ReviewersPMP Study Peer Reviewers1Contractor TeamProbable Maximum Precipitation (PMP)Coverage of HMRsHow Do PMP Studies Provide Improved PMP Values?Method for Computing PMP ValuesMethod for Computing PMP Values1�PMP Study for Texas �PMP Study for Texas PMP Study for Texas PMP Study for Texas �Issues to ConsiderPMP Study for Texas1 �PMP Study for Texas12 �Intermediate Storm List-All Storms�Storms used for PMP DevelopmentPMP Study for Texas 1PMP Study for Texas4 PMP Study for Texas 5Probable Maximum Precipitation Study for Texas�PMP Study for Texas 6PMP Study for Texas 7PMP Study for Texas�PMP Study for Texas8 PMP Study for TexasPMP Study for Texas9 NOAA Atlas 14 Precip Frequency Coverage��Probable Maximum Precipitation Study for Texas��Example PMP Map-DRAFTPrecipitation Frequency Map34What is nextWhen will it be availableProductProposed date availableGrace PeriodDam Safety Section �TCEQ�MC-177�P. O. Box 13087�Austin, Texas 78711�warren.samuelson@tceq.texas.gov�(512/239-5195)�johnny.cosgrove@tceq.texas.gov�(512/239-4307)�Questions