National Weather Service (NWS) – Part 2

Precipitation-Frequency
Probable Maximum Precipitation
Presenter:
Geoff Bonnin
Office of Hydrologic Development, National Weather Service, NOAA
Email: [email protected]
Web: www.nws.noaa.gov/oh/hdsc
Authors:
Geoffrey Bonnin, Deborah Martin, Sandra Pavlovic, Sanja Perica, Ishani
Roy, Michael St Laurent, Carl Trypaluk, Dale Unruh
National Dam Safety Program
Technical Seminar No. 21
February 19-20, 2014
Topics
1.
Precipitation Frequency Estimates
2.
Probable Maximum Precipitation
3.
Probabilistic Flood Hazard Assessment
4.
Potential Impact of Climate Change
NOAA Atlas 14 Volumes
 NOAA/NWS/Hydrometeorological Design Studies Center (HDSC)
 precipitation frequency estimates on behalf of the Federal Government
 Referenced in many Federal, state and local government regulations
Updates are
published as
Volumes of
NOAA Atlas 14
Application: Infrastructure design
 Examples:
 Control of water: Flood mitigation,
land development and construction ,
storm water drainage (roads, parking
lots, airports, land, roofs), culverts,
bridges,...
 Utilization of water for beneficial
purposes: water supply, irrigation,
navigation, hydrolectric-power
development, ...
Water-quality management
Mays, Water Resources Handbook, McGraw-Hill, 1996
Precipitation frequency (PF)
estimate definition
 Frequency:

AMS: Annual exceedance probability – AEP

PDS: Average recurrence interval – ARI

eg: amount with1% chance of being exceeded once or more than once

in any given year (AEP = 1%)

on average, will be exceeded only once in 100 years (ARI = 100yr)
 PF estimate:
Precipitation Depth (or Intensity) for a given Duration and Frequency (AEP or ARI)
Depth-Duration-Frequency (DDF) curves
Depth
Frequency
Intensity-Duration-Frequency (IDF) curves
Duration
Annual maximum series (AMS) vs.
partial duration series (PDS)
AMS
PDS
 AMS-based frequency analysis used in NOAA 14
 PDS-based (for ARI) PF estimates calculated
 directly for early Volumes
 indirectly from Langbein’s formula for later Volumes
Where to go find NOAA Atlas 14 products?
Precipitation Frequency Data Server (PFDS):
http://hdsc.nws.noaa.gov/hdsc/pfds/index.html
NOAA Atlas 14 Volumes – performance statistics
MW
SE
CA
PR
SW
ORB
AK
HI
PI
NOAA Atlas 14 interactive
web page (upper part)
NOAA Atlas 14 interactive web page
… PF estimate (with confidence limits)
.
PF graphical: DDF curves,
confidence intervals
Cartographic maps
Maps were created to serve as visual aids and are not
recommended for interpolating estimates.
Precipitation frequency estimates in GIS
compatible format (30 arc-sec resolution)
 PDS: 570 grids (190 quantile; 190 upper CL; 190 lower CL)
 AMS: 513 grids (171 quantile; 171 upper CL; 171 lower CL)
 Temporal distributions of
amounts exceeding 2-year
magnitudes provided for 6-hour,
12-hour, 24-hour, and 96-hour
durations for delineated climate
regions.
 Four precipitation cases;
defined by the duration quartile in
which the greatest percentage of
the total precipitation occurred.
c) 24-hour duration
100
Cumulative percent of precipitation
.
Supplementary information:
Temporal distributions
90
80
70
90%
60
50
10%
50%
40
30
20
10
0
0
10 20 30 40 50 60 70 80 90 100
Cumulative percent of duration
.
Supplementary information
Seasonality analysis
.
Supplementary information
Time series data
.
Supplementary information
Documentation
Comparison with superseded studies
 Main differences in available products:
• NA14: 30 arc-sec gridded estimates
- Estimates up to 1,000 years ARI
- Confidence intervals
- Supplementary info.
• Superseded documents: paper maps with isopluvials
– Estimates up to 100 years ARI
 Main differences in methodologies:
• Statistical methodology
• Spatial interpolation techniques (topographic features)
• Available data (number of stations and record lengths)
24-hr 100-yr NA14 vs. TP40
Probable Maximum Precipitation (PMP)
.
 Theoretically greatest depth of precipitation, for a given
duration, physically possible, over a given size storm area,
at a particular geographic location
• “Worst case”, “perfect storm”, “the most the atmosphere can pump”
 Used in design of large dams
 PMP used to estimate Probable Maximum Flood
Status of PMP Estimates
.
 Very old empirical methodology needs updating
•
There is doubt about the old estimates
 Very little data collection since 1972 generally
• 1986 in some areas
 Interagency committee tasked with proposing update plan
• Little progress to date
• USACE, USBR, NRC, each with internal plans & programs
• Several States are going it alone
- Produces inconsistency
NWS Maintains Old PMP Documents
.
Probabilistic Flood Hazard Assessment?
.
 What about design between 1,000 yr ARI and PMP?
•
•
•
•
Agencies design and asset management want risk based approach
NA14 doesn’t go beyond 1,000 years because of large uncertainty
There is doubt about PMP estimates and methodology
More research is needed
•
“Workshop on Probabilistic Flood Hazard Assessment”, Jan 2013
http://www.nrc.gov/public-involve/public-meetings/meeting-archives/research-wkshps.html
.
Can Climate Change
Make the “Perfect Storm” More Perfect?
World and U.S. Record Rainfall
.
Potential Impact of Climate Change
on Precipitation Frequency
Contact us:
Email: [email protected]
Web: www.nws.noaa.gov/oh/hdsc
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