a baseline climatology of precipitation rates that induce flash flooding in an urban environment
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A Baseline Climatology of Precipitation Rates that Induce Flash Flooding in an Urban Environment. Suzanne M. Fortin National Weather Service Pleasant Hill/Kansas City October 19, 2005. Objectives. - PowerPoint PPT PresentationTRANSCRIPT
A Baseline Climatology of A Baseline Climatology of Precipitation Rates that Precipitation Rates that
Induce Flash Flooding in an Induce Flash Flooding in an Urban EnvironmentUrban Environment
Suzanne M. FortinSuzanne M. FortinNational Weather ServiceNational Weather ServicePleasant Hill/Kansas CityPleasant Hill/Kansas City
October 19, 2005October 19, 2005
ObjectivesObjectives• To perform a quantitative assessment To perform a quantitative assessment of short duration, extreme rain rates of short duration, extreme rain rates and historical precipitation return and historical precipitation return frequencies in the Kansas City frequencies in the Kansas City metropolitan area and surrounding metropolitan area and surrounding regionregion
• Downscale U.S.-scale precipitation Downscale U.S.-scale precipitation frequency estimates utilizing HPD and frequency estimates utilizing HPD and Alert systemAlert system
• Build runoff return frequencies for the Build runoff return frequencies for the urban areaurban area
• Integrate precipitation and runoff Integrate precipitation and runoff frequencies to build excess runoff frequencies to build excess runoff climatologyclimatology
Why?Why?
Kansas City has a history of extreme flooding and flash Kansas City has a history of extreme flooding and flash flooding.flooding.
Several news-worthy extreme flash flooding events in the Several news-worthy extreme flash flooding events in the past 50 years, with four extreme events occurring in the past 50 years, with four extreme events occurring in the past 30 years.past 30 years.
Intense/extreme precipitation events have increased Intense/extreme precipitation events have increased across CONUS (Knight, 1988)across CONUS (Knight, 1988)
Operational forecaster rule of thumb for flash flooding Operational forecaster rule of thumb for flash flooding onset is outdated.onset is outdated.
““Recent extreme” rain events and data excluded Recent extreme” rain events and data excluded Current technology – WSR-88D and Flash Flood Current technology – WSR-88D and Flash Flood
Monitoring and Prediction program – often detect rain Monitoring and Prediction program – often detect rain rates 3-4-5”/hourrates 3-4-5”/hour
CaveatsCaveats
Will not address meteorological conditions Will not address meteorological conditions associated with extreme rain events in Missouri associated with extreme rain events in Missouri and eastern Kansas (Junker, 1993; Moore, 1995 and eastern Kansas (Junker, 1993; Moore, 1995 & various; Glass, 1998; Glass et al., 1995; & various; Glass, 1998; Glass et al., 1995; Maddox et al., 1979).Maddox et al., 1979).
Will not address WSR-88D rain rate climatologyWill not address WSR-88D rain rate climatology
Historical rain ratesHistorical rain ratesExtreme Rainfall
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5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
0.02 0.08 0.23 0.25 0.5 0.7 1 1.33 2.75 3 4.5 12 18 24
Duration (Hours)
Rai
nfa
ll D
epth
(in
)
KC HPD Rainfall Depth (in)
OP/KC Alert Rainfall Depth (in)
U.S. Rainfall Depth (in)
Urban Flash Flood HydrologyUrban Flash Flood Hydrology By definition (NWS), flash By definition (NWS), flash
flood producing rains have flood producing rains have durations of six hours or lessdurations of six hours or less
Onset of flooding in urban Onset of flooding in urban areas much greater due to areas much greater due to impervious surfaces, disruption impervious surfaces, disruption of natural water balance, of natural water balance, increased flood peaks (Young, increased flood peaks (Young, H.Y, 2000; Sauer et al., 1983)H.Y, 2000; Sauer et al., 1983)
Four of the most significant Four of the most significant flash flood episodes in the past flash flood episodes in the past 25 years in the urban core of 25 years in the urban core of Kansas City have occurred Kansas City have occurred within 1 to 3 hours of the onset within 1 to 3 hours of the onset of rain, producing twice the of rain, producing twice the quantity of rain indicated in quantity of rain indicated in NWS Hydro-35 (NOAA, 1977) NWS Hydro-35 (NOAA, 1977)
Urban Flash Flood HydrologyUrban Flash Flood Hydrology Storm water treatment and design typically Storm water treatment and design typically
utilize 10 year, 24-hour, 90% rainfall event for utilize 10 year, 24-hour, 90% rainfall event for cost mitigation (SWRC, 1998)cost mitigation (SWRC, 1998)
Analysis of KC storm water design found system Analysis of KC storm water design found system will accommodate 1.37”/hour (Young & will accommodate 1.37”/hour (Young & McEnroe, 2002)McEnroe, 2002)
Runoff return rates at other durations and Runoff return rates at other durations and frequencies difficult to obtain/accessfrequencies difficult to obtain/access
Design rather than geomorphology dictate level Design rather than geomorphology dictate level of excess – a difficult concept for forecasters to of excess – a difficult concept for forecasters to grasp grasp
Comparison of Rainfall Comparison of Rainfall FrequenciesFrequencies
HYDRO-35 Precipitation Frequency
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1.00
2.00
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4.00
5.00
6.00
1.00 2.00 3.00 6.00
Hours
Rai
nfa
ll (i
n)
1-year
2-year
5-year
10-year
25-year
50-year
100-year
Overland Park/KC Alert Rainfall Frequency
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
0.08 0.1 0.25 0.5 1 2 3 6 12 24
Duration (Hours)
Rai
nfa
ll D
epth
(in
)
1-year
2-year
5-year
10-year
25-year
50-year
100-year
Courtesy of OPSWM
Revised 60-minute Rainfall Revised 60-minute Rainfall Frequency Curve for Kansas CityFrequency Curve for Kansas City
Utilized QC’d hourly Utilized QC’d hourly precipitation data from 20 precipitation data from 20 HPD sitesHPD sites
Developed frequency Developed frequency distribution of rainfall distribution of rainfall categories categories ≥≥1.0 (NOAA 1.0 (NOAA Hydro35, Young & Hydro35, Young & McEnroe, 2002)McEnroe, 2002)
Utilized Hydro35 Utilized Hydro35 regression equations to regression equations to develop revised develop revised distributiondistribution
Comparison of 60-minute Rainfall Frequencies
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
1-Year RainfallDepth (in)
2-Year RainfallDepth (in)
5-Year RainfallDepth (in)
10-Year RainfallDepth (in)
25-Year RainfallDepth (in)
50-Year RainfallDepth (in)
100-Year RainfallDepth (in)
Return Period
Rai
nfa
ll D
epth
(in
)
60-Minute Adjusted Rainfall Frequency 60-Minute Hydro35 Rainfall Frequency 60-minute OP/KC Alert Rainfall Frequency
Revised Kansas City Rainfall Frequency
0
1
2
3
4
5
6
7
8
9
10
1-Year RainfallDepth (in)
2-Year RainfallDepth (in)
5-Year RainfallDepth (in)
10-Year RainfallDepth (in)
25-Year RainfallDepth (in)
50-Year RainfallDepth (in)
100-Year RainfallDepth (in)
Return Rate
Rai
nfa
ll (i
n)
1 hour 2-hour 3-hour 6-hour 12-hour 24-hour
Revised KC Precipitation Revised KC Precipitation FrequencyFrequency
Revised Kansas City Rainfall Frequency (HPD and Alert)
0
1
2
3
4
5
6
7
8
9
10
1-Year RainfallDepth (in)
2-Year RainfallDepth (in)
5-Year RainfallDepth (in)
10-Year RainfallDepth (in)
25-Year RainfallDepth (in)
50-Year RainfallDepth (in)
100-Year RainfallDepth (in)
Duration
Rai
nfa
ll (i
n)
1-Hour
2-Hour
3-Hour
6-Hour
12-Hour
24-Hour
ConclusionsConclusions
Downscaling of rainfall frequencies indicate Downscaling of rainfall frequencies indicate rates greater than values from Hydro35rates greater than values from Hydro35
Developing excess runoff return frequencies not Developing excess runoff return frequencies not as tangible, but have something to build uponas tangible, but have something to build upon
Integrate rainfall/excess runoff frequency to Integrate rainfall/excess runoff frequency to establish urban FFTI establish urban FFTI
Based on rainfall rate frequencies, KC urban Based on rainfall rate frequencies, KC urban core will need to continue to enhance storm core will need to continue to enhance storm water design to mitigate floodingwater design to mitigate flooding
Important to take advantage of recent, dense Important to take advantage of recent, dense data networksdata networks
Future ResearchFuture Research
Recalibrate coefficients for return frequenciesRecalibrate coefficients for return frequencies Expand analysis to develop frequency curves Expand analysis to develop frequency curves
based on 15-, 30-, 90-, 120-minute data (ASOS, based on 15-, 30-, 90-, 120-minute data (ASOS, Alert, DCP)Alert, DCP)
Reprocess data utilizing PDF employed by Reprocess data utilizing PDF employed by Young & McEnroe, 2002 and Angel & Huff, 1992Young & McEnroe, 2002 and Angel & Huff, 1992
Work with local storm water management Work with local storm water management groups to establish excess runoff frequenciesgroups to establish excess runoff frequencies