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Comparative Precipitation Analysis and Validation of NEXRAD (Stage III)
Data, Stream Flow Data, and Rain Gauge Data located
in the San Antonio River Basin
Jayar S. Griffith
ES5053
Fall 2004
Outline
I. Title
II. Author
III. Abstract
IV. Introduction
V. Methods
VI. Analysis
VII. Conclusion
VIII. Tables and Figures
IX. Reference
I. Title of the project or paper reviewed
Comparative Precipitation Analysis and Validation of NEXRAD (Stage
III) Data, Stream Flow Data, and Rain Gauge Data located in the San
Antonio River Basin
II. Name(s) or authors of the paper reviewed
Jayar S. Griffith
III. Abstract
This remote sensing project is a comparative precipitation analysis and
validation of (NEXRAD Stage III) data, stream flow data, and rain gauge data
located in the San Antonio River Basin. Validation of NEXRAD Stage III
data with stream flow data and rain gauge data is used to analyze flooding
events and create more accurate hydrologic models. This study deve lops the
understanding for the process of data collection of Hourly Precipitation
NEXRAD Data, Hourly Stream Flow Data, and Hourly Rain Gauge Data by a
variety of internet sources. During this project, data management, file
conversion, and analysis using ArcGIS 9 was used for data comparison. This
paper does not involve analysis of NEXRAD Stage III data with Rain Gauge
data due to the lack of access and reformatting of the National Oceanic and
Atmospheric Administration website.
IV. Introduction
The region of study for this project is the 10,800 km2 area of the San
Antonio River Basin. Heavy rainfall events during 1998 and 2002 in the San
Antonio River Basin have resulted in two major flooding disasters. The 1998
flooding event created major flash flooding along major streams and rivers
along South Central Texas and resulted in the loss of 31 lives and over three
quarters of a billion dollars in property damage (National Oceanic and
Atmospheric Administration Service Assessment, 1999). These major
flooding events have increased the concern for better NEXRAD rainfall
products to analyze rainfall events and improve flood warning predictions.
This remote sensing project introduces the fundamental concepts of how
NEXRAD data is used for analyzing rainfall events and its relation with Rain
Gauge data and Stream Flow data. The improved functionality and analysis
of Geographic Information Systems (GIS) was applied to illustrate hourly
precipitation NEXRAD Stage III data for the month of October 2004 over the
San Antonio River Basin.
V. Methods
Data Collection
The process to complete this project is as follows: Data collection using
the internet, data management and conversion, importing to ArcGIS grid with
a defined projection, data analysis using ArcGIS Spatial Analyst tool and
Excel Spreadsheet.
The first step in this project is collection of Hourly Rain Gauge data
located in the San Antonio River Basin that is used by the NOAA. During a
continuous search of free accessible data through National Climatic Data
Center website (http://nndc.noaa.gov), a problem of accessing hourly
precipitation for each COOP# Rain Gauge Station occurred because of a
reformat of the NCDC data access website. Rain gauge data must be
purchased for a fee for Hourly Precipitation format. This prob lem resulted in
no NEXRAD Stage III and Rain Gauge analysis in this project.
This project involved a process of data mining of Hourly NEXRAD Stage
III data and USGS Stream Flow data using the internet. The location of where
to find the NEXRAD Stage III data from National Weather Service Regional
Forecast Center located in New Braunfels, Texas is
http://dipper.nws.noaa.gov/hdsb/data/nexrad/wgrfc_stageiii.html (Xie,
RS5053 Lecture 10). This data is monthly precipitation Stage III data of the
New Braunfels regional forecast area and is formatted in binary multi-tarred
files and is converted to ArcGIS grid files by a process (Figure 1) created by
Dr. Hongjie Xie (Xie et al., 2003). During this process, binary multi-tarred
files of the October NEXRAD Stage III data are decompressed to ASCII files
by a process of Unix Perl Script. The ASCII files were converted to ArcGIS
grid files by using an AML Script in Arc Workstation and defining the grid
files as polar-stereographic and re-projected to Texas Centric NAD83 Albers
(Xie, et al, 2003). Final conversion of October NEXRAD Stage III data
allowed projection using ArcGIS in 4km pixel spatial resolution. Each pixel
is associated with a precipitation value in millimeters.
Hourly Stream Flow data was collected from the United States Geological
Survey Real Time Stream Flow website (http://waterdata.usgs.gov/nwis/rt).
The network of USGS Stream Flow gauges is located along major creeks
and rivers in the San Antonio River Basin like Medina River, Cibolo Creek,
Salado Creek, Leon Creek, Upper and Lower San Antonio River. Hourly 15
min stream flow data for each stream flow gauge station can be downloaded
with in the last 31 days from the present day of access through the USGS
website. Any previous date after 31 days will result in averaged hourly
discharge and not in 15 min increments. This data was collected for the date
range from October 8, 2004 zero hour to November 8, 2004, 22nd hour.
Hourly stream flow data was converted from Text files to Excel Spreadsheet
and organized by station ID. Each USGS Stream Flow gauge station was
sub-totaled by the sum of the discharge (cfs) per hour. Discharge in cubic feet
per second were converted to cubic meters per hour. A rainfall event from
October 24, 2004-16th hour to October 25, 2004-04th hour is used to compare
with NEXRAD Stage III data (Figure 2, Sample of USGS Hourly Stream
Flow Data for Station ID 8181500).
ArcGIS Shapefiles of the San Antonio Basin, Rain Gauge locations, and
USGS Stream Flow Stations were provided by Dr. Hongjie Xie. These
shapefiles were re-projected from Assumed Geographic to Texas Centric
NAD83 Albers by the use of the Data Management Tool provided in Arc Tool
Box of ArcGIS. Individual shapefiles of the San Antonio Basin were created
into four sub-regions: Medina, Cibolo, Upper San Antonio, and Lower San
Antonio. A 2km buffer was established around each individual sub-region to
calculate only the amount of precipitation over that region.
VI. Analysis
A rainfall event from October 24, 2004-16th hour to October 25, 2004-04th
hour is used to compare NEXRAD Stage III data with USGS Stream Flow
data. Using ArcGIS, the sum of total precipitation over a 2km buffer of the
Medina sub-region was calculated by the Zonal Statistic tool in ArcGIS. The
sum of precipitation for each hour from October 24, 2004-16th hour to October
25, 2004-04th hour was calculated and imported to an Excel spreadsheet
(Figure 3). The precipitation is measured in millimeters and converted to
meters. Multiplying the zonal statistic sum for each hour over the Medina
sub-region by the area of the Medina sub-region will give the volume in cubic
meters.
USGS Stream Flow gauge 8181500 was used because it was located at the
bottom of the Medina River in the Medina sub-region. Hourly stream flow
data of the same rainfall event from October 24, 2004-16th hour to October 25,
2004-04th hour was used. The discharge rate in cubic meters is used to
compare with the volume (zonal statistic sum per hour) in cubic meters
(Figure 3).
A chart of NEXRAD Stage III data versus Hourly USGS Stream Flow
data for the rainfall event from October 24, 2004-16th hour to October 25,
2004-04th hour was created (Figure 4). This chart did not correlate the
relationship between NEXRAD data and Stream Flow data. Further analysis
and guidance from Dr. Hongjie Xie identified the problem. During the time
of organizing the USGS Stream Flow data to an Excel spreadsheet, the wrong
time zone conversion was used. USGS Stream Flow data is measured in
Central Time Zone and NEXRAD Stage III data is measured in Universal
Time Zone resulting in a 6 hour difference and discrepancy as shown in
Figure 4.
A new Excel spreadsheet was created with the adjusted time of the USGS
stream flow data versus NEXRAD Stage III data. This data has a greater
number in cubic meters in stream flow discharge per hour in the Medina
sub-region (Figure 5). A more accurate representation of the increased
precipitation and increased stream flow relationship is shown in Figure 6.
This chart can be used to validate the NEXRAD data with the Stream
Flow data for future research.
VII. Conclusion
Hourly rain gauge data was unavailable for this project due to the lack
access and reformatting of the NCDC website. Further search for available
rain gauge data is needed to validate the NEXRAD Stage III data.
During the process of data collection and management, the knowledge of
converting binary multi-tarred Stage III data to ASCII files and then
converting to ArcGIS grid was demonstrated. Using the file conversion
process created by Dr. Hongjie Xie made a faster and easier process of using
the NEXRAD Stage III data in GIS. Future projects will consist of migrating
the NEXRAD Stage III data to a local network server for easier access and for
a larger memory space location.
This project also demonstrated the fundamentals of using ArcGIS and the
functionality of Spatial Analyst and Projection tools needed to complete this
project. Applying the NEXRAD grid data with ArcGIS Shapefiles developed
a useful illustration of a rainfall event over the San Antonio Basin (Figure 7).
Using this data with conjunction with USGS stream flow data concluded in
validating the idea that an increase in precipitation will result in an increase in
stream flow.
VIII. Tables and Figures
I. NEXRAD Stage III Data Conversion
Figure 1 Xie et al, 2003
II. Sample of USGS Hourly Stream Flow Data for Station ID 8181500
discharge Hour m
USGS 8181500 10/10/2004 9:15 4.48 185 10 737 20.86948
USGS 8181500 10/10/2004 9:30 4.48 185 10 716 20.27483
USGS 8181500 10/10/2004 9:45 4.47 184 10 709 20.07661
USGS 8181500 10/10/2004 10:00 4.46 183 10 704 19.93503
737 10 Total 710 20.10493
USGS 8181500 10/10/2004 10:15 4.45 181 11 733 20.75621
USGS 8181500 10/10/2004 10:30 4.44 180 11 762 21.5774
USGS 8181500 10/10/2004 10:45 4.43 178 11 802 22.71007
USGS 8181500 10/10/2004 11:00 4.42 177 11 838 23.72948
716 11 Total 857 24.2675
USGS 8181500 10/10/2004 11:15 4.42 177 12 864 24.46572
USGS 8181500 10/10/2004 11:30 4.43 178 12 861 24.38076
USGS 8181500 10/10/2004 11:45 4.42 177 12 852 24.12591
Figure 2
III. Excel Spreadsheet of NEXRAD Stage III (Zonal Statistic sum) versus
Hourly USGS Stream Flow Data (Station #8181500)
Zonal Statistics with
"Medina_L2_Buffer"
Medina Area =
3.49801 X10^9 sq
meters
USGS Stream Flow
Gauge
# 8181500
sum,
Hourly Precip. Hour mm sum, m area NEXRAD(volume cubic m) Discharge, cubic m
r10242004_16z 16 0 0 3.49801E+09 0.00E+00 269.29
r10242004_17z 17 0 0 3.49801E+09 0.00E+00 314.60
r10242004_18z 18 1.75 0.00175 3.49801E+09 6.12E+06 315.73
r10242004_19z 19 37.12 0.03712 3.49801E+09 1.30E+08 293.36
r10242004_20z 20 618.54 0.61854 3.49801E+09 2.16E+09 293.36
r10242004_21z 21 1656.59 1.65659 3.49801E+09 5.79E+09 287.42
r10242004_22z 22 1350.61 1.35061 3.49801E+09 4.72E+09 266.46
r10242004_23z 23 834.82 0.83482 3.49801E+09 2.92E+09 253.44
r10252004_00z 0 439.24 0.43924 3.49801E+09 1.54E+09 258.82
r10252004_01z 1 570.25 0.57025 3.49801E+09 1.99E+09 255.13
r10252004_02z 2 333.6 0.3336 3.49801E+09 1.17E+09 250.32
r10252004_03z 3 67.33 0.06733 3.49801E+09 2.36E+08 243.81
r10252004_04z 4 0.18 0.00018 3.49801E+09 6.30E+05 243.81
Figure 3
IV. Chart of Excel Spreadsheet of NEXRAD Stage III (Zonal Statistic
sum) versus Hourly USGS Stream Flow Data (Station #8181500)
NEXRAD vs Stream Flow (Medina Watershed)
350.00
300.00
250.00
Stream Flow (cubic meters)
200.00
Series1
150.00
100.00
50.00
0.00
0.00E+00 1.00E+09 2.00E+09 3.00E+09 4.00E+09 5.00E+09 6.00E+09 7.00E+09
NEXRAD (cubic meters)
Figure 4
V. Excel Spreadsheet of Correct Time Zone of NEXRAD Stage III (Zonal
Statistic sum) versus Hourly USGS Stream Flow Data (Station
#8181500)
Zonal Statistics with "Medina_L2_Buffer"
Medina Area = 3.49801 X10^9 sq meters
USGS Stream Flow Gauge
#81818500
Hourly Precip. Hour sum, mm sum, m area NEXRAD(volume cubic m) discharge, m
r10242004_16z 16 0 0 3.49801E+09 0.00E+00 0
r10242004_17z 17 0 0 3.49801E+09 0.00E+00 0
r10242004_18z 18 1.75 0.00175 3.49801E+09 6.12E+06 173341.7867
r10242004_19z 19 37.12 0.03712 3.49801E+09 1.30E+08 3676826.928
r10242004_20z 20 618.54 0.61854 3.49801E+09 2.16E+09 61267902.16
r10242004_21z 21 1656.59 1.65659 3.49801E+09 5.79E+09 164089297.4
r10242004_22z 22 1350.61 1.35061 3.49801E+09 4.72E+09 133781228.9
r10242004_23z 23 834.82 0.83482 3.49801E+09 2.92E+09 82690965.95
r10252004_00z 0 439.24 0.43924 3.49801E+09 1.54E+09 43507797.95
r10252004_01z 1 570.25 0.57025 3.49801E+09 1.99E+09 56484659.37
r10252004_02z 2 333.6 0.3336 3.49801E+09 1.17E+09 33043897.18
r10252004_03z 3 67.33 0.06733 3.49801E+09 2.36E+08 6669201.429
r10252004_04z 4 0.18 0.00018 3.49801E+09 6.30E+05 17829.44092
Figure 5
V. Final Chart of Correct Time Zone of NEXRAD Stage III (Zonal
Statistic sum) versus Hourly USGS Stream Flow Data (Station
#8181500)
NEXRAD vs Stream Flow
180000000
160000000
140000000
120000000
Stream Flow (cubic m)
100000000
discharge, m
Linear (discharge, m)
80000000
60000000
40000000
20000000
0
0.00E+00 1.00E+09 2.00E+09 3.00E+09 4.00E+09 5.00E+09 6.00E+09 7.00E+09
NEXRAD (cubic m)
Figure 6
VI. GIS Layout of NEXRAD Stage III Grid data over San Antonio River
Basin
Hourly Precipitation
10242004_23
-
r10242004_23z
Value
0 - 1.389999986
1.389999987 - 5.090000153
0 25 50 100 Miles
5.090000154 - 10.64999962
10.64999963 - 18.12000084
18.12000085 - 28.20999908 Created by: Jayar S. Griffith
11/24/2004 RS5053 Project
28.20999909 - 48.74000168 Source: USGS, NOAA, TNRIS, Dr. Hongjie Xie
Projection: NAD 1983 Albers
Figure 7
IX. References
National Oceanic and Atmospheric Administration. South Texas Floods
October 17-22, 1998. Service Assessment February 1999
Xie, H., X. Zhou, E.R. Vivoni, J.M.H. Hendrickx. E.E. Small, 2005. GIS
GIS Based NEXRAD Precipitation Database: Automated Automated
Approaches for Data Processing and Visualization. Computers and
Geosciences, Vol. 31, pp. 65-76.
Xie, Hongjie, 2004 Power Point Slides: L10-Water. 2004
NEXRAD Stage III data available at:
http://dipper.nws.noaa.gov/hdsb/data/nexrad/wgrfc_stageiii.html
USGS Real Time Stream Flow Data available at:
http://waterdata.usgs.gov/nwis/rt
