Site-Specific and Regional Probable Maximum Precipitation (PMP) Studies Ed Tomlinson, PhD 2009 Western Regional Dam Safety Forum San Francisco, California January 15, 2009 PO Box 680 Monument, Co 80132 (719) 488-9117 e-mail: [email protected]www.appliedweatherassociates.com Site-Specific and Regional PMP Studies – Current HMRs – Completed Site-Specific and Regional Studies – Key Tasks – Procedures – Examples
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Site-Specific and RegionalProbable Maximum Precipitation
(PMP) Studies
Ed Tomlinson, PhD
2009 Western Regional Dam Safety ForumSan Francisco, California
–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
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
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
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
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
Approach for Nebraska StatewideProbable Maximum Precipitation
(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
Approach for Nebraska StatewideProbable Maximum Precipitation
(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?
Approach for Nebraska StatewideProbable Maximum Precipitation
(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)
Approach for Nebraska StatewideProbable Maximum Precipitation
(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
Approach for Nebraska StatewideProbable Maximum Precipitation
(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
Approach for Nebraska StatewideProbable Maximum Precipitation
(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
Approach for Nebraska StatewideProbable Maximum Precipitation
(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
–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
Nebraska Statewide ProbableMaximum Precipitation (PMP) Study
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
Nebraska Statewide ProbableMaximum Precipitation (PMP) Study
24-Hour Long List of Storms•Searched for and extracted the archived
NCDC hourly datasets for the 24-hrmaximum precipitation within the definesearch box–Greater than 6.0 inches
•138 storms identified
Nebraska Statewide ProbableMaximum Precipitation (PMP) Study
48-Hour Long List of Storms•Searched for and extracted the archived
NCDC hourly datasets for the 48-hrmaximum precipitation within the definesearch box–Greater than 7.5 inches
•155 storms identified
Nebraska Statewide ProbableMaximum Precipitation (PMP) Study
466 storms were included on the Long List ofStorms
Nebraska Statewide ProbableMaximum Precipitation (PMP) Study
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