Flash Floods poster

•The spatial pattern of flash flood warnings suggests the warning forecast favor
counties with higher populations.
•Extreme rainfall events in 2002 and 2004 exaggerate the findings for the later
time period of this analysis.
1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
Comparison Bexar County
More than four times the number of warnings were issued from 1996-2005 compared to 1986-1995. There is also an increase in the number of warnings issued between 2001-2006 compared to 1995-2000.
R²
P-Value
< 0.001
•Compare flash flood warnings and reports to physiographic features known to have an
influence on flash flooding. •Compare the spatial distribution of flood monitoring stations to flash flood warnings and reports. •Determine exact false alarm rates for each county in the study area. •Test the theory that the population of certain counties can tolerate a higher number of false alarms. •Compare correlations of population demographics to flash flood warnings and reports. •Build a warning systems computer model that can test various influences on flash flood warning forecast decisions. Contact: KB1499@
AP Photo/ Waco Tribune Herald, Jerry Larson
0.63
0.33 0.16 0.19 0.17
0.43
The purpose of this study is to spatially analyze flash flood warnings issued
by the National Weather Service office in New Braunfels, Texas to determine if there are patterns related to population and government severe weather warning policy.
Purpose
Warnings 86-95 & Reports 86-95 Warnings 96-05 & Reports 96-05 Warnings 95-00 & Reports 95-00 Warnings 01-06 & Reports 01-06
0.82 0.83 0.85 0.73
Statistical comparisons show a very high correlation between warnings and reports.
flood reports suggest a low false alarm rate.
Single County Analysis
Warnings 1986-2006 Bexar County
60 50 40 30 20 10 0
National Weather Service Modernization
Further Study
Warnings 93-06 & Reports 93-06
0.87
The above map comparison illustrates the drastic increase in the number of flash flood warnings issued after the National Weather Service modernization effort.
R²
0.39 0.17
P-Value
0.025 0.344 < 0.001 0.061 0.374 0.290 0.344 0.013 < 0.001 < 0.001 < 0.001 < 0.001
Reports 86-95 & Population
Reports 96-05 & Population Warnings 95-00 & Population Warnings 01-06 & Population Reports 95-00 & Population Reports 01-06 & Population
•National Weather Service modernization corresponds to an overall increase in the
number of flash flood warnings issued.
Findings
•The strong statistical correlation between flash flood warnings issued and flash
© 2009
Texas State University-San Marcos
Statistical Analysis
Comparison
Warnings 86-95 & Population Warnings 96-05 & Population
Post National Weather Service Modernization
The study area is the 33 county warning area (CWA) covered by the National Weather Service Office located at New Braunfels, Texas. The most populated counties are Bexar (1,392,931) and Travis (812,280). Population data are from the United States Census Bureau 2000 census.
Austin Houston San Antonio
The above maps compare warnings and reports for time periods after the National Weather Service modernization. The majority oቤተ መጻሕፍቲ ባይዱ warnings and reports are from the more populated counties in the study area.
All flash flood warning data from the National Weather Service. All flash flood report data from the National Climatic Data Center.
The most populated county in the study area is Bexar. The number of warnings for this county increased drastically after the National Weather Service modernization effort, starting in 1997. In 2002 and 2004, significant rain events caused major flooding for the county. The county shows a high statistical correlation for issued warnings and flash flood reports for the time period of 1993-2006 (1993 is the first year that accurate flash flood reports are available).
Study Area
Dallas
Graph Comparison
4000 3500 3000 2500 2000 1500 1000 500 0 1986-1995 1996-2005 Warnings 4000 3500 3000 2500 2000 1500 1000 500 0 1995-2000 2001-2006 Warnings Reports
An Evaluation of Flash Flood Warnings and Flash Flood Reports for South Central Texas
Kevin Barrett
Abstract
Flash flood warnings issued by the Austin/San Antonio forecast office of the National Weather Service from 1986 to 2006 were spatially evaluated to find possible trends related to population growth and change in government severe weather warning policy. It was found that almost three times the number of warnings were issued in the five year time period of 2001 to 2006 compared to the decadal time period of 1986 to 1995, with the highest number of warnings trending to center on urban areas and the location of the National Weather Service office. When the warnings are compared to actual flash flood reports, a strong statistical correlation exists suggesting a low false alarm rate for the area. Results indicate that National Weather Service modernization, technological upgrades in flood monitoring, public awareness of flood dangers and population growth may be factors contributing to the spatial distribution of warnings.