site-specific and regional pmp studies...site-specific and regional probable maximum precipitation...

Site-Specific and RegionalProbable Maximum Precipitation

(PMP) Studies

Ed Tomlinson, PhD

2009 Western Regional Dam Safety ForumSan Francisco, California

January 15, 2009

PO Box 680Monument, Co 80132

(719) 488-9117e-mail: [email protected]

www.appliedweatherassociates.com

Site-Specific and Regional PMPStudies

–Current HMRs–Completed Site-Specific and Regional Studies–Key Tasks–Procedures–Examples

Probable Maximum Precipitation

•Definition: The theoreticallytheoretically greatest depth ofprecipitation for a given duration that is physicallyphysicallypossiblepossible over a given storm area at a particulargeographic locationgeographic location at a certain time of year(HMR 59, 1999)

•Types of PMP studies:–Generalized (Hydrometeorological Reports, HMRs)–Site-Specific

•Individual drainage basin•Regional

CurrentNWSHMRs

Regional PMP Studies

EPRI Wisconsin/Michigan PMP Study1993

Nebraska Statewide PMP Study2008

Arizona Statewide PMP StudyBegin Feb 2009

Recent FERC Approved Site-Specific PMP Studies

Upper and Middle DamsFPLE Maine Hydro 2003

Great Lake Sacandaga/Stewarts BridgeReliant Energy 2005

Blenheim Gilboa Pump Storage 2008New York Power Authority

Current FERC PMP Studies

Lewis River, WashingtonPacifiCorp Initiated Nov 2008

State Site-Specific PMP Studies

ApprovedColoradoOhioNew JerseyNebraskaNew York

Potential new studiesOregonCaliforniaVirginiaPennsylvania

Method for ComputingPMP Values

•No physically based theoretical method (yet)•Observed extreme rainfall events are used•Three primary steps

––MaximizationMaximization procedures are applied––TranspositioningTranspositioning procedures are applied––EnvelopingEnveloping procedures are applied

•Storm separation method used inHMRs 57 & 59

Do Site-Specific PMP Studies ProvideImproved PMP Values?

•Attributes:–More storms considered–New technologies used–Problems in the HMRs corrected–Topographic features addressed

Key Tasks for Site-Specific PMPStudies

• Identify extreme storm types–Evaluate the use of HMR procedures for each storm

type• Identify unique topography

–Moisture depletion by upwind mountain barriers–Precipitation enhancement/decrease–Effects on storm center location

•Review HMR procedures used for the basin location–Identify inconsistent assumptions

Examples of Site-SpecificPMP Study Findings

•Homogeneous Climate Regions

–Select stormsfor eachregion

–Transpositiononly in thesame region

Examples of Site-SpecificPMP Study Findings

•Storm Maximization, Dewpoint Analyses–12-hour vs 6-hour persisting dewpoints–12-hour persisting vs 6-hour average

•Observed dewpoint values• Hour 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20• Td 68 67 69 69 72 75 75 74 75 73 70 69 68 65 66 65 65 65 67 66• ! Rainfall Event !

• 12-hour persisting: 65• 6-hour persisting: 72• 6-hour average: 74

Updated Procedures•Maximum Dewpoint Climatology

–HMR 59 produced new dewpoint climatologies•3- and 12- persisting maximum dewpoint values

–Nebraska statewide PMP study produced newdewpoint climatologies•6-, 12-, and 24-hour average dewpoint values•20-, 50- and 100-year return frequencies

•Sea surface temperatures used for some storms–Subjective techniques used in HMRs 57 & 59

•Not documented–Objectives techniques used in other site-specific

PMP studies

Recalculation of the Distance from theCoast curve in HMR 51

Examples of Site-Specific PMP Study

Results

•FPL Maine Hydro Upperand Middles Dams–Upwind moisture barrier

defined–Sea surface temperatures

used

HysplitUpwindTrajectories

Barrier MoistureDepletion Analysis

Southeastern Inflow Barrier - South Arm to Sugarloaf MountainAverage Barrier Height - 830 Meters / 2725 Feet

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1 51 101 151 201 251 301 351 401 451 501 551 601 651 701 751 801 851 901 951 1001 1051

Cell Number

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rier

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eter

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Examples of Site-Specific PMPStudy Results

S o utheast M oisture Inf lo w Barrie r - The G reen, B erkshire, and Taco nic M o untainsA verage B arrie r H eight M inus 100 Feet: 2040 F eet

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B ar r ier W idth in M i les

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A verage B arrie r H eight A verage Barrie r H eight M inus 100 F eet B arrier Terra in H eight

Northeast Moisture Inflow Barriers:Tuxedo Lake Drainage Basin

Effective Barrier Height: 1400 feet

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Barrier 1 Average Elevation Barrier 2 Average Elevation

Northeast Inflow Barrier 2 Northeast Inflow Barrier 1

Effective Barrier Height

Northeast Inflow Barrier 1Average Elevation: 1,461 feetLength: 66 miles

Northeast Inflow Barrier 2Average Elevation: 1,230 feetLength: 85 miles

WithinBasinOrographics

WithinBasinOrographics

Within BasinOrographics

Temporal Transposition Date 17-AugLat Long SSE@ 75 miles

Stormcenter location 36.23 N 96.57 W 1,300 feet

StormRepdewpoint location 35.23 N 96.06 W Storm Elevation 930 feetTransposition dewpoint location 40.20 N 95.88 W 1,300 feetBasin location 41.25 N 96.66 W

76.0 F with total precipitable water above sea level of 2.99 inches.79.0 F with total precipitable water above sea level of 3.44 inches.80.0 F with total precipitable water above sea level of 3.60 inches.930 which subtracts 0.24 inches of precipitable water at 76.0 F930 which subtracts 0.27 inches of precipitable water at 79.0 F

1,300 which subtracts 0.38 inches of precipitable water at 80.0 F1,300 which subtracts 0.38 inches of precipitable water at 80.0 F

1.151.021.00

1.17

6 Hours 12 Hours 18 Hours 24 Hours 30 Hours 36 Hours 48 Hours 60 Hours 72 Hours18.4 23.4 23.6 23.6 23.6 23.6 0.0 0.0 0.014.7 19.2 19.4 19.6 19.7 19.8 0.0 0.0 0.012.5 17.6 17.8 18.0 18.1 18.3 0.0 0.0 0.09.7 15.4 15.6 15.7 15.8 16.2 0.0 0.0 0.07.9 13.3 13.4 13.6 13.7 14.1 0.0 0.0 0.04.3 7.3 7.4 7.5 7.7 7.8 0.0 0.0 0.03.0 5.3 5.4 5.5 5.6 5.7 0.0 0.0 0.02.0 3.9 4.1 4.2 4.3 4.4 0.0 0.0 0.0


Storm or StormCenter Name Hallett, OKStorm Date(s) 2-Sep-1940Storm Type MCCStorm Location 36.23 N 96.57 WStorm Center Elevation 930Precipitation Total & Duration 24.00 Inches 12-hours USACE Storm Studies SW 2-18

Storm Representative Dewpoint 76.0 F 12hr averageStorm Representative Dewpoint Location 35.23 N 96.06 WMaximumDewpoint 79.0 FMoisture Inflow Vector SSE@ 75 MilesIn-place Maximization Factor 1.15

Temporal Transposition (Date) 17-AugTransposition Dewpoint Location 40.20 N 95.88 WTransposition Maximum Dewpoint 80.0 FBasin Elevation 1,300Transposition to Basin Adjustment Factor 1.02Higher of Basin Elevation - Inflow Barrier Height 1,300Elevation Adjustment Factor 1.00Total Adjustment Factor 1.17

200 sq miles500 sq miles


The barrier adjustment factor is

The total adjustment factor is

The inflow barrier/basin elevation height is

The transposition/elevation to basin factor is

Hallett, OKStormName:StormDate:AWA Analysis Date: 5/10/2007

02-Sep-1940


1000 sq miles


10 sq miles

5000 sq miles10000 sq miles20000 sq miles

Storm Adjustment for Wanahoo, NE

AdjustedStorm Depth-Area-Duration

ObservedStormDepth-Area-Duration


The in-place stormmaximization factor is

The in-place storm elevation isThe transposition basin elevation at

Moisture InflowDirection:Basin Elevation

Effective Barrier HeightNotes: DAD values taken fromUSACEStorm Studies SW 2-18

The storm representative dew point isThe in-place maximumdew point is

The transpositioned maximumdew point isThe in-place storm elevation is

Stormor StormCenter Name Hallett, OKStormDate(s) 2-Sep-1940StormType MCCStormLocation 36.23 N 96.57 WStormCenter Elevation 930Precipitation Total & Duration 24.00 Inches 12-hours USACE StormStudies SW 2-18

StormRepresentative Dewpoint 76.0 F 12hr averageStormRepresentative Dewpoint Location 35.23 N 96.06 WMaximumDewpoint 79.0 FMoisture Inflow Vector SSE @ 75 MilesIn-place Maximization Factor 1.15

Temporal Transposition (Date) 17-AugTransposition Dewpoint Location 40.20 N 95.88 WTransposition MaximumDewpoint 80.0 FBasin Elevation 1,300Transposition to Basin Adjustment Factor 1.02Higher of Basin Elevation - Inflow Barrier Height 1,300Elevation Adjustment Factor 1.00Total Adjustment Factor 1.17

Temporal Transposition Date 17-AugLat Long SSE@ 75 miles

Stormcenter location 36.23 N 96.57 W 1,300 feet

StormRepdew point location 35.23 N 96.06 W Storm Elevation 930 feetTransposition dewpoint location 40.20 N 95.88 W 1,300 feetBasin location 41.25 N 96.66 W

76.0 F with total precipitable water above sea level of 2.99 inches.79.0 F with total precipitable water above sea level of 3.44 inches.80.0 F with total precipitable water above sea level of 3.60 inches.930 which subtracts 0.24 inches of precipitable water at 76.0 F930 which subtracts 0.27 inches of precipitable water at 79.0 F

1,300 which subtracts 0.38 inches of precipitable water at 80.0 F1,300 which subtracts 0.38 inches of precipitable water at 80.0 F

1.151.021.00

1.17

The barrier adjustment factor is

The total adjustment factor is

The inflow barrier/basin elevation height is

The transposition/elevation to basin factor is

Hallett, OKStormName:StormDate:AWA Analysis Date: 5/10/2007

02-Sep-1940 Storm Adjustment for Wanahoo, NE

The in-place stormmaximization factor is

The in-place stormelevation isThe transposition basin elevation at

Moisture Inflow Direction:Basin Elevation

Effective Barrier HeightNotes: DAD values taken fromUSACEStorm Studies SW 2-18

The stormrepresentative dew point isThe in-place maximum dew point is

The transpositioned maximum dew point isThe in-place stormelevation is






1000 sq miles


10 sq miles


AdjustedStorm Depth-Area-Duration

Observed Storm Depth-Area-Duration


Example of Site-SpecificDepth-Area Storm Analysis

Twenty-Four-Hour Depth-Area Curves for Maximized and TranspositionedStorm Events In the Great Sacandaga Lake Drainage Basin

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Rainfall Depth in Inches

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Westfield, MassachusettsEaston, MarylandBuck, ConnecticutZerbe, PennsylvaniaPaterson, New JerseyYork, PennsylvaniaPeekamoose, New YorkGorham, MaineHector, New YorkNear Bolton, CanadaRipogenus Dam, MaineCanton, ConnecticutSt. Pierre Baptiste, CanadaNewark, New JerseyHartford, CtEnveloping CurveHMR 51

Approach for Nebraska StatewideProbable Maximum Precipitation

(PMP) Study

•The statewide PMP study was initiated with asite-specific PMP study for the Wanahoodrainage basin

•Peer reviewers–Pat Diederich

•Nebraska Dam Safety

–Mark Anderson, PhD•University of Nebraska

–Barry Keim, PhD•LSU


(PMP) Study

•Objective: PMP analysis that includescomprehensive evaluations of extremerainfall storm events–Extreme rainfall storm identification–Storm analyses of recent storms–Storm maximization–Storm transpositioning


(PMP) Study

•Storm based methodology–Identify historic extreme rainfall events–Analyze the storm Depth-Area-Duration (DAD) rainfall

amounts•What was the actual storm rainfall?

–Maximize the storm rainfall “in-place”•How much more rainfall could the storm have potentially

produced if more moisture were available?

–Transposition the storm to Nebraska•Had the storm occurred in Nebraska, what would have been the

maximum rainfall produced?


(PMP) Study

–Complete a storm search to identify the most significantstorms that could have potentially occurred overvarious locations in Nebraska•Over 35 years since the newest storm in HMR 51•Extreme rainfall storms that occurred over the midwestern US

–A review of characteristics associated each storm typewill be provided•Synoptic storm systems•Mesoscale Convective Complexes (MCCs)


(PMP) Study

–For storms not previously analyzed, stormisohyetal and depth-area-duration (DAD)analyses were completed•Eight new storms identified, seven have been analyzed•Maximization and transposition factors determined

for new storms and re-evaluated for old storms


(PMP) Study

–Perform storm maximization and transpositioning ofthe most extreme storms various regions in Nebraska

–6-hour, 12-hour and 24-hour average maximumdewpoint values were used for storm maximization andtranspositioning

–New 6-hour, 12-hour and 24-hour average maximumdewpoint climatologies were computed•GEV distribution used•20-year, 50-year and 100-year maps were produced


(PMP) Study–Continuity in time and space for all the final

PMP values–Comparisons with HMR 51 values

•Explanations of the differences are being preparedwhere possible

•Since working papers for HMR 51 are not available,it may not possible to explain the source of thedifferences between site-specific PMP values andthe generalized HMR 51 PMP values


(PMP) Study–Create a grid covering Nebraska and portions of

surrounding states–Perform storm maximization and transpositioning of

the most extreme storms to each of the grid pointlocations

–6-hour, 12-hour and 24-hour maximum averagedewpoint values will be used for storm maximizationand transpositioning

–DAD curves for the largest transpositioned andmaximized storms will be plotted at each grid point

Proposed Grid for Use in the NebraskaStatewide PMP Study

Nebraska Statewide ProbableMaximum Precipitation (PMP) Study•Storm Search

–Search the National Climatic Data Center (NCDC)hourly and daily rainfall records

–Identify maximum 6-hr, 24-hr/1-day, and 72-hr/3-day rainfall amounts within a the search box•(49.0/-108.0, 49.0/-85.0, 35.0/-108.0, and 35.0/-85.0)

–Additional data mining was done using the NationalWeather Service (NWS), National Oceanic andAtmospheric Administration (NOAA), and NCDCweb services, various American MeteorologicalSociety (AMS) journals, and Google internet stormsearches

Nebraska Statewide ProbableMaximum Precipitation (PMP) Study

StormSearchBox With

Stormeventlocationsfor themaximum6-hrrainfallstormsearch


6-Hour Long List of Storms•Searched for and extracted the archived

NCDC hourly datasets for the 6-hrmaximum precipitation within the definesearch box–Greater than 4.5 inches

•169 storms identified










466 storms were included on the Long List ofStorms


36 storms were included on theShort List of extreme storms

22 storms were used in HMR 516 storms were identified in the EPRI study8 storms identified in the storm search

Storm PrecipitationAnalysis System

(SPAS)

•SPAS …is a complete storm analysis software programis a unique state-of-the-art storm centered depth-area-duration (DAD) analysis systemuses the latest advancements of GeographicInformation Systems (GISs)is largely automated, yet requires and allows plentyof user (SPAS meteorologist) intervention.uses the same basic principles used by theNational Weather Bureau

- Consistency is achieved

What is SPAS?

•Analyze major storms that have occurred since themid-50’s

•Analyze current flood producing storms immediatelyafter they occur

•Re-analyze historic storms

Storm Analyses Uses

Storm Precipitation AnalysisSystem (SPAS)

•The Weather Bureau and the Corps ofEngineers completed detailed stormanalyses for storms that occurredfrom the 1880’s through the 1950’s

•Since the the 1950’s only a few selected storms have been analyzed(e.g. Hurricanes Camille 1969 andAgnes 1972)

•Site-specific PMP studies requirestorm analyses

•Runoff model calibration andvalidation greatly benefit fromaccurate and detailed storm analyses

Examples ofSite-SpecificPMP Study

Results

SPASStormAnalysisvsNWSAnalysis

•The DAD resultscompared favorably topreviously analyzedstorms, including:1. Westfield, MA, storm

of August 17-20,1955

2. Ritter, IA storm ofJune 7, 1953

SPAS vs NWSDAD

SPASSq-Miles 6-hour 12-hour 24-hour 36-hour 48-hour 60-hour Tota l

10 7.96 11.48 16.40 19.10 19.11 19.47 19.70100 7.22 10.72 15.20 17.77 17.76 18.23 18.47200 6.99 10.27 14.28 16.91 16.84 17.39 17.54

1000 5.97 9.06 12.55 14.97 15.08 15.40 15.955000 4.14 6.45 9.25 11.70 12.02 12.35 13.05

10000 3.23 5.46 7.63 9.60 9.91 10.26 10.8620000 2.24 4.03 5.91 7.66 7.97 8.22 8.77

W eathe r BureauSq-Miles 6-hour 12-hour 24-hour 36-hour 48-hour 60-hour Tota l

10 7.80 11.10 16.40 18.90 19.40 19.40 19.40100 7.60 10.50 14.60 18.10 18.80 19.00 19.00200 7.40 10.20 14.20 17.60 18.20 18.40 18.40

1000 6.20 9.20 12.40 15.90 16.20 16.40 16.405000 4.00 6.30 9.50 12.10 12.60 13.00 13.00

10000 3.10 5.00 8.00 10.00 10.60 10.80 10.8020000 2.10 3.60 6.30 7.90 8.30 8.50 8.50

Perce nt Diffe renceSq-Miles 6-hour 12-hour 24-hour 36-hour 48-hour 60-hour Tota l

10 2.1% 3.4% 0.0% 1.1% -1.5% 0.4% 1.5%100 -5.0% 2.1% 4.1% -1.8% -5.5% -4.1% -2.8%200 -5.5% 0.7% 0.6% -3.9% -7.5% -5.5% -4.7%

1000 -3.7% -1.5% 1.2% -5.8% -6.9% -6.1% -2.7%5000 3.5% 2.4% -2.6% -3.3% -4.6% -5.0% 0.4%

10000 4.2% 9.2% -4.6% -4.0% -6.5% -5.0% 0.6%20000 6.7% 11.9% -6.2% -3.0% -4.0% -3.3% 3.2%

Generally within +/- 5% !!

•Total storm–sum of allhourly grids/maps.

Total storm (HurricaneFloyd) precipitation, NewJersey, September 14-18,1999.

SPAS OutputTotal Storm Map

•The hourlyprecipitation gridsserve as the basis formuch of the outputstatistics

Hourly precipitationending at 4 PM ESTSeptember 16, 1999associated withHurricane Floyd.

Methodology (cont.)

Hourly Precipitation Grids (cont.)

Use of NEXRAD Weather RadarData in SPAS Rainfall Analyses

–NEXRAD data are correlated with hourlyrain gauge data•For each hour, coefficients are selected based on

the least square fit of the the Z-R equation to theavailable hourly rainfall observations

•Rainfall amounts are computed for the domaincovered by the NEXRAD

–Result•Rainfall amounts are analyzed

–For each hour of the storm–At a spatial resolution of approximately 1 square

kilometer

Storm 1033 - Ogallala, NE July 6 (300 Z) - July 7 (600 Z), 2002

MAXIMUM AVERAGE DEPTH OF PRECIPITATION (INCHES)Duration (hours)

Area (mi2) 1 2 3 4 5 6 12 18 24 28 total

1 5.18 6.51 8.45 10.06 11.61 13.19 14.77 14.78 14.92 14.92 14.9210 3.90 5.40 7.95 9.53 11.04 12.54 14.39 14.41 14.53 14.57 14.5720 3.52 5.23 7.65 9.17 10.66 12.12 14.00 14.01 14.12 14.16 14.1630 3.28 5.12 7.47 8.93 10.38 11.79 13.57 13.60 13.74 13.74 13.7440 3.10 4.96 7.30 8.69 10.08 11.47 13.22 13.25 13.36 13.39 13.3950 2.95 4.86 7.14 8.50 9.85 11.18 12.90 12.93 13.05 13.08 13.0860 2.83 4.75 7.00 8.29 9.57 10.90 12.61 12.63 12.77 12.78 12.7870 2.71 4.64 6.85 8.13 9.41 10.65 12.34 12.36 12.50 12.51 12.51

100 2.39 4.37 6.46 7.67 8.88 10.06 11.66 11.69 11.84 11.84 11.84200 2.09 3.72 5.49 6.69 7.78 8.79 10.22 10.30 10.46 10.46 10.46500 1.65 2.89 4.09 5.07 6.04 6.70 8.14 8.34 8.50 8.51 8.51

1,000 1.19 2.21 3.06 3.82 4.54 5.11 6.24 6.59 6.75 6.76 6.765,000 0.41 0.84 1.11 1.40 1.72 2.00 2.68 3.09 3.23 3.25 3.25

NEXRAD Mass Curves

Six-Hour Depth-Area Curves for Maximized and TranspositionedStorm Events In the Lake Wanahoo Drainage Basin

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Stor

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Big Rapids, MIBonaparte, IABoyden, IACollinsville, ILCooper, MICouncil Grove, KSEdgerton, MOGrant Township, NEGreeley, NEIda Grove, IAHayward, WIHMR 51Hallett, OKIronwood, MILambert, MNMedford, WIMeeker, OKMinneapolis, MNParis Waterworks, INRitter, IAStanton, NETomah, WIWarner, OKCole Camp, MOBeaulieu, MNEnid, OKForest City, MNHale, COHolly, COOgallala, NEPawnee Creek, COSavageton, WYSpringbrook, MT

Seventy-Two-Hour Depth-Area Curves for Maximized and TranspositionedStorm Events In the Lake Wanahoo Drainage Basin

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sBeaulieu, MNBig Rapids, MIBoyden, IACollinsville, ILCouncil Grove, KSEdgerton, MOHayward, WIIronwood, MILambert, MNMedford, WIMeeker, OKStanton, NEWarner, OKHMR 51Cole Camp, MOEnid, OKForest City, MNPawnee Creek, COSavageton, WYSpringbrook, MTDavid City, NEPrague, NEEnvelop

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site-specific and regional pmp studies...site-specific and regional probable maximum precipitation...

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