Environment

 

Precipitation Frequency

 

Precipitation Frequency in the Southeastern Wisconsin Region

 

NOAA Atlas 14, Precipitation-Frequency Atlas of the United States, Volume 8, Version 2.0: Midwestern States (Colorado, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Oklahoma, South Dakota, Wisconsin), published in 2013, presents the most-current precipitation depth-duration-frequency information for the State of Wisconsin and the seven-county Southeastern Wisconsin Region. The Wisconsin portion of the NOAA study that produced Atlas 14 was funded by the Wisconsin Departments of Natural Resources (WDNR) and Transportation (WisDOT) and SEWRPC. The Atlas 14, volume 8, version 2.0 report can be accessed at: http://www.nws.noaa.gov/oh/hdsc/PF_documents/Atlas14_Volume8.pdf

The information in Atlas 14 supersedes that in SEWRPC Technical Report No. 40, and the Commission staff recommends that Atlas 14 precipitation data be used in stormwater and floodland management applications. The SEWRPC storm time distribution issued on March 30, 2006, is still recommended by SEWRPC for use in stormwater and floodland management applications, including regulatory floodplain mapping studies, in the Southeastern Wisconsin Region.

Atlas 14 precipitation-frequency data for durations from 5 minutes to 60 days and frequencies of one through 1,000 years is provided in tabular and graphical formats and as geographic information system(GIS)-compatible ASCII grids on the NOAA Hydrometeorological Design Studies Center Precipitation Frequency Data Server (PFDS) at: http://hdsc.nws.noaa.gov/hdsc/pfds/ Generalized maps of the data are also provided, but NOAA recommends use of the PFDS point-and-click interface or the GIS-compatible ASCII grids to obtain precipitation values for analysis purposes.

The SEWRPC staff has coordinated with the United States Department of Agriculture Natural Resources Conservation Service (NRCS), WDNR, and WisDOT regarding the application of Atlas 14 in Wisconsin. NRCS is in the process of developing average precipitation frequency information for various depths, durations, and frequencies for each county in the State of Wisconsin and they are also developing new 24-hour storm time distributions consistent with the Atlas 14 precipitation information. WDNR has indicated that the NRCS time distributions applicable to the Southeastern Wisconsin Region or the 2006 SEWRPC distribution set forth below in Table 1 and Figure 1 will be acceptable for studies to delineate regulatory one-percent-annual-probability (100-year recurrence interval) floodplain boundaries. A description of the procedure used to develop the SEWRPC distribution can be found here.

The SEWRPC recommended rainfall distribution was developed for a range of storm durations and depths.  Therefore, unlike the 24-hour  U.S. Natural Resources Conservation Service Type II distribution, it is not characteristic of a single duration. It is recommended that the SEWRPC distribution be applied to develop design storms for a range of durations and the storm, or storms, producing the highest peak flow(s) be used for analysis purposes.

A joint NRCS/SEWRPC presentation on Atlas 14 provides summary information on the development and application of Atlas 14 precipitation frequency information.

                                             Table 1

               SEWRPC RECOMMENDED RAINFALL DISTRIBUTION

 

Percent
of Total Storm Time

Cumulative Percent of
Total Storm Rain

0
0.0
5
2.7
10
4.8
15
6.9
20
9.5
25
13.2
30
18.9
35
28.5
40
42.2
45
56.6
50
68.4
55
76.5
60
81.6
65
85.2
70
88.0
75
90.3
80
92.2
85
94.0
90
95.8
95
97.7
100
100.0

Source: SEWRPC

 

 

Characterization of the June 2008 and July 2010 Heavy Rains in the Southeastern Wisconsin Region

 

The probabilities of the heavy rains of June 2008 and July 2010 for various durations from one-hour through 10 days were characterized using information from the NOAA Atlas 14, Volume 8, Version 2.0 Precipitation Frequency Data Server as set forth in Tables 2 and 3.

 

Rainfall Patterns for Storms of August 1986, June 1997, and August 1998

 

Map 1, Rainfall Pattern Over Southeastern Wisconsin 24-Hour Period on August 6, 1986

Map 2, Rainfall Pattern Over Southeastern Wisconsin 26-Hour Storm on June 20-21, 1997

Map 3, Rainfall Pattern Over Southeastern Wisconsin 24-Hour Period on August 6, 1998

 

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Southeastern Wisconsin Regional Planning Commission

 

W239 N1812 Rockwood Drive
P.O. Box 1607
Waukesha, WI 53187-1607

 

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8:00 a.m. - 4:30 p.m.

 

Phone: (262) 547-6721
Fax: (262) 547-1103
E-mail: sewrpc@sewrpc.org