USGS Water Resources
DIGITAL-MAP GRIDS OF MEAN-ANNUAL PRECIPITATION FOR 1961-90, AND GENERALIZED SKEW COEFFICIENTS OF ANNUAL MAXIMUM STREAMFLOW FOR OKLAHOMA

By Alan Rea and Robert L. Tortorelli
U.S. Geological Survey Open-File Report 97-574

Prepared in cooperation with the
Oklahoma Department of Transportation

Oklahoma City, Oklahoma
1997

TABLE OF CONTENTS

Abstract
Introduction
File formats
Data Organization
Geometric Registration
Notes
References Cited

ABSTRACT

This digital report contains two digital-map grids of data that were used to develop peak-flow regression equations in Tortorelli, 1997, "Techniques for estimating peak-streamflow frequency for unregulated streams and streams regulated by small floodwater retarding structures in Oklahoma," U.S. Geological Survey Water-Resources Investigations Report 97-4202. One data set is a grid of mean annual precipitation, in inches, based on the period 1961-90, for Oklahoma. The data set was derived from the PRISM (Parameter-elevation Regressions on Independent Slopes Model) mean annual precipitation grid for the United States, developed by Daly, Neilson, and Phillips (1994, "A statistical-topographic model for mapping climatological precipitation over mountainous terrain:" Journal of Applied Meteorology, v. 33, no. 2, p. 140-158).

The second data set is a grid of generalized skew coefficients of logarithms of annual maximum streamflow for Oklahoma streams less than or equal to 2,510 square miles in drainage area. This grid of skew coefficients is taken from figure 11 of Tortorelli and Bergman, 1985, "Techniques for estimating flood peak discharges for unregulated streams and streams regulated by small floodwater retarding structures in Oklahoma," U.S. Geological Survey Water-Resources Investigations Report 84-4358. To save disk space, the skew coefficient values have been multiplied by 100 and rounded to integers with two significant digits. The data sets are provided in an ASCII grid format.

INTRODUCTION

This digital report contains two digital-map grids of data that were used to develop peak-flow regression equations in Tortorelli (1997). One data set is a grid of mean annual precipitation, in inches, based on the period 1961-90, for Oklahoma. The data set was derived from the PRISM (Parameter-elevation Regressions on Independent Slopes Model) mean annual precipitation grid for the United States, developed by Daly, Neilson, and Phillips (1994).

The second data set is a grid of generalized skew coefficients of logarithms of annual maximum streamflow for Oklahoma streams less than or equal to 2,510 square miles in drainage area. This grid of skew coefficients is taken from figure 11 of Tortorelli and Bergman, (1985). To save disk space, the skew coefficient values have A documentation file (known as metadata) for each data set is provided. Graphic images also are provided in Graphics Interchange Format (GIF) files.

The U.S. Geological Survey compiled these data sets in cooperation with the Oklahoma Department of Transportation.

FILE FORMATS

The two data sets are provided in an ASCII grid file format. The first six lines of each file contain the number of columns and rows in the grid, the map coordinates of the lower-left grid cell, the grid cell size in meters, and the value used to indicate a missing value (-9999, also called "NODATA").

The "SKEWGRID.ASC" file is compressed with the GZIP utility. The GUNZIP utility is an MS-DOS executable program that will uncompress the data file. The file should first be copied to hard disk. To uncompress the file, type at the MS-DOS prompt: GUNZIP -aN SKEWGRID.GZ

This will uncompress the file and restore its original name, "SKEWGRID.ASC".

The documentation files comply with the Federal Geographic Data Committee (FGDC) Content Standards for Digital Geospatial Metadata (Federal Geographic Data Committee, 1994).  The FGDC-compliant metadata files contain detailed descriptions of the data sets, and include narrative sections describing the procedures used to produce the data sets in digital form.

A graphic image also is provided in a Graphics Interchange Format (GIF) file. GIF files are easily displayed on a variety of computer systems using readily available display software. This image provides a simplified view of the data sets, and may be used for browsing purposes. The GIF file portrays significantly less spatial resolution and information content than the actual data sets.

DATA ORGANIZATION

A_NOTICE.TXT
Liability disclaimer
PRECIP.GIF
A GIF image of an illustration from Tortorelli (1997) showing lines of equal mean annual precipitation, in inches, for 1961-90
MAPRECIP.ASC
Mean Annual Precipitation ASCII grid, in inches
MAPRECIP.PRJ
Map-projection parameters for the mean annual precipitation data set
MAPRECIP.HTML
Complete documentation of the data sources and procedures used to create the mean annual precipitation grid
SKEW.GIF
A GIF image of an illustration from Tortorelli (1997) showing lines of equal generalized peak skew coefficients
SKEWGRID.GZ
Generalized peak skew coefficients ASCII grid, multiplied by 100 and rounded to two significant digits (Compressed with GZIP)
SKEWGRID.PRJ
Map-projection parameters for the generalized peak skew coefficients data set
SKEWGRID.HTML
Complete documentation of the data sources and procedures used to create the generalized peak skew coefficients data set

GEOMETRIC REGISTRATION

The Albers Equal Area map projection (Snyder, 1987) is used for the data sets.  This projection is appropriate for maps of Oklahoma because of the visual presentation and equal-area characteristic, which facilitates areal analysis.  The projection is cast on the North American Datum of 1983. The following table provides map projection information.

This projection slightly distorts shapes and distances (scale) in order to maintain equal-area properties.  Scale is true along the standard parallels (Snyder, 1987).

Albers Equal Area projection parameters
[GRS1980, Geodetic Reference System; 1980 NAD83, North American Datum 1983]
Projection parameters:
SpheroidGRS1980
DatumNAD83
First standard parallel34 00 00 North
Second standard parallel36 30 00 North
Central meridian98 00 00 West
Latitude of projection origin33 00 00 North
Coordinate system parameters:
False easting0
False northing0
Planimetric units of measure meters

NOTES

The use of trade names is for descriptive purposes only, and does not imply endorsement by the U.S. Government.

The data sets were processed using the ARC/INFO Revision 7.0.3 software package, running on a Data General AViiON workstation. File names, directories, and pathnames in this document are enclosed in quotation marks, and type set in upper case. Pathnames use MS-DOS-style naming conventions, with the "\" character indicating the highest-level directory of the diskette.

REFERENCES CITED

Daly, C., R.P. Neilson, and D.L. Phillips, 1994, A statistical- topographic model for mapping climatological precipitation over mountainous terrain: Journal of Applied Meteorology, v. 33, no. 2, p. 140-158. Federal Geographic Data Committee, 1994, Content standards for digital geospatial metadata (June 8): Federal Geographic Data Committee, Washington, D.C., 78 p.

Snyder, J.P., 1987, Map projections--A working manual: U.S. Geological Survey Professional Paper 1395, 383 p.

Tortorelli, R.L., 1997, Techniques for estimating peak-streamflow frequency for unregulated streams and streams regulated by small floodwater retarding structures in Oklahoma: U.S. Geological Survey Water-Resources Investigations Report 97-4202, 39 p.

Tortorelli, R.L., and Bergman, D.L., 1985, Techniques for estimating flood peak discharges for unregulated streams and streams regulated by small floodwater retarding structures in Oklahoma: U.S. Geological Survey Water-Resources Investigations Report 84-4358, 85 p.


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