Transcript What is Extreme Precipitation?

EXTREME
PRECIPITATION
Prepared by Lesley Sweeney
Environmental Engineer, CT NRCS
November, 2012
What is Extreme Precipitation?
• A large precipitation event
• Design storm of a given duration with a
Recurrence (or frequency) of 1yr -500yr
(e.g. 10-year 24-hour rainfall)
• NOT the amount of Annual Rainfall
Recurrence is all about
probability…
• 100-yr Storm
1 / 100 = 1% chance of occurrence in any year
• 25-yr Storm
1 / 25 = 4% chance of occurrence in any year
• 2-yr Storm
1 / 2 = 50% chance of occurrence in any year
• 1-yr Storm
1 / 1 = 100% chance of occurrence??? 99.9% chance
Climate Change?
Changes in Extreme Precipitation?
Increases in Amounts of Very Heavy
Precipitation (1958 to 2007)
The map shows percent increases in the amount falling
in very heavy precipitation events (defined as the heaviest 1 percent of all daily events) from 1958 to 2007 for
each region. There are clear trends toward more very
heavy precipitation for the nation as a whole, and particularly in the Northeast and Midwest.
U.S. Global Change Research Program. 2009. Global
climate change impacts in the United States: a state of
knowledge report. Cambridge [England]: Cambridge
University Press.
DeGaetano, Arthur T., 2009: Time-Dependent
Changes in Extreme-Precipitation ReturnPeriod Amounts in the Continental United
States. J. Appl. Meteor. Climatol., 48, 2086–
2099.
History of Extreme Precipitation
Technical Paper 40 (1961)
NOAA Atlas 14 (2004)
Wilks (1993)
NRCC (2010)
Northeast Regional Climate Center web site:
www.precip.net
Joint collaboration
between:
•Northeast Regional Climate Center
(NRCC)
NOAA Regional Climate Centers,
Applied Climate Information
System (ACIS), National Climatic
Data Center (NCDC), and Cornell
University
•Natural Resources Conservation
Service (NRCS)
Maine, Vermont, New Hampshire,
Massachusetts, Rhode Island,
Connecticut, and New York
6
Project Goals
• Create an updated, comprehensive extreme
precipitation atlas for the Northeast US.
• Match the products and output of NOAA Atlas 14
for NRCS compatibility.
• Add additional products to supplement NRCS
hydrologic design.
• Produce real-time monitoring and climate change
tools.
Scope of Data/Output
N-minute
Hourly
Daily
Years
States
5min
1hr
1day
1yr
Connecticut
2yr
Maine
5yr
Massachusetts
10min
2hr
2day
15min
3hr
4day
10yr
New Hampshire
30min
6hr
7day
25yr
New York
60min
12hr
10day
50yr
Rhode Island
100yr
Vermont
200yr
(surrounding states)
500yr
(Canada)
120min
24hr
48hr
Replaced Publications used by
NRCS
• Technical Paper 40, 1961. 30-minute to 24hour for 1-year to 100-year return periods.
• NWS HYDRO-35, 1977. 5- to 60- Minute
Precipitation Frequency for the Eastern and
Central United States.
• Technical Paper 49, 1964. Two- to Ten- Day
Precipitation for Return Periods of 2 to 100
years.
NRCC vs. TP-40 10-year 24-hour,
percent more or less
NRCC vs. TP-40 100-year 24-hour,
percent more or less
NRCC – Hydro35 10-year 60-min
percent more or less
NRCC vs. Hydro35 100-year 60-min.,
percent more or less
NRCC vs. TP-49 100-year 10-day,
percent more or less
Precipitation Trends
• NRCC data shows general increase as
return period gets larger for 60-minute
and 24-hour durations.
• NRCC 100-year 10-day precipitation
trend is lower on average.
Old Rainfall Distributions
Steps in developing a distribution
• Determine ratios of  hour : 24 hour rainfall.
• Place the rainfall ratio for the shortest duration
in the center of the distribution.
• Symmetrically place each larger duration to
include the shorter durations.
Example distribution
30 min
10 min
0.6
5 min
3 hr
6 hr
0.7
Site and Storm Frequency-Specific
Distribution Curves
How does this translate to design
runoff in Connecticut?
• Generally for the 1 yr-10 yr 24-hr storm, no
large change in runoff.
• For the 50 yr and 100 yr 24-hr storm, likely
higher runoff due to higher precipitation
amounts .
• The 25 yr 24-hr storm trends towards higher
due to increased rainfall amount but may be
moderated by the rainfall distribution.
Rainfall Distribution Comparison
300
6
1-ac CN = 65
5
100-ac CN = 65
250
200
4
NE C
3
NE D
2
TYPE III
NE C
150
NE D
100
Type III
50
1
0
0
1-yr
2-yr
40
5-yr
10-yr
25-yr
1-yr
50-yr 100-yr
5-yr
1600
10-ac CN = 65
35
2-yr
25-yr
50-yr 100-yr
1000-ac CN = 65
1400
30
10-yr
1200
25
20
15
10
NE C
1000
NE D
800
Type III
600
NE C
NE D
Type III
400
5
200
0
1-yr
2-yr
5-yr
10-yr
25-yr
50-yr 100-yr
0
1-yr
2-yr
5-yr
10-yr
25-yr
50-yr 100-yr
Getting Data from www.precip.net
NRCS Runoff Calculation Tools
• WinTR-20,
compatible to import rainfall table and create
distribution curves
• WinTR-55
Accepts individual storms and individual distribution
curves. 2 Methods to implement the data
• EFH2
County rainfall files and regional distribution curves
will be added
Importing NRCC data into WinTR-20
Importing data into WinTR-20
Importing data into WinTR-20
Importing data into WinTR-20
• Select “Import NOAA
–NRCC Data” from
“File” pulldown menu.
• Locate the directory,
select text file name
“CT_Windham.txt”
Importing data into WinTR-20
Using NRCC data with WinTR-55
Two Methods
• Using County Data
Typical method using representative
county precipitation values developed
using the NRCC data and regionalized
rainfall distributions
• Using Site Specific Data
Each frequency storm is run separately
County Rainfall for WinTR-55
Rainfall data at the geographical county centroid.
Regional Rainfall Distribution Curves
WinTR-55 Example using County Data
WinTR-55 Example using County Data
Using Site Specific Data in WinTR-55
Using Site Specific Data in WinTR-55
Conclusions
• Precipitation amounts have not changed
significantly for 1yr-10 yr 24-hour design storms
• Precipitation amounts have increased for 25 yr
and above 24-hour design storms
• New site and storm specific Rainfall Distributions
• New extreme precipitation data can be used with
NRCS programs to determine design storm runoff
References
1.
2.
3.
4.
www.precip.net Outreach Presentations
Evaluating Runoff Predictions from Rainfall Tables and Generalized Distribution
Curves for EFH-2 and WinTR-20 in New York State, Paper Number: 121338007,
Peter Wright State Conservation Engineer USDA NRCS NY
Design Rainfall Distributions Based on NOAA Atlas 14 Powerpoint, Geoffrey
Cerrelli, P.E. Hydraulic Engineer USDA NRCS PA, ASABE – 2010 Conference.
Using Northeast Regional Climate Center Extreme Precipitation Data with
WinTR-55 in Connecticut, Ben Smith, USDA NRCS CT, May 2012
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Slide 46
NOTICE TO HISPANIC OR WOMAN FARMERS
If you are a woman or Hispanic farmer and you believe you were denied farm loan
benefits by USDA between 1981 and 2000, you may be eligible for compensation.
For more information, call 1-888-508-4429 or visit www.farmerclaims.gov.
Information about USDA civil rights cases can be found online at:
a. Hispanic or Women Farmers
www.farmersclaims.gov or call 1-888-508-4429
b. Black Famers
www.blackfarmercase.com or call 1-888-950-5547.
c. Native American Farmers
www.IndianFarmClass.com or call 1-888-233-5506.
Questions?
Lesley Sweeney
Environmental Engineer
860-429-1084
[email protected]