Metadata: Identification_Information: Citation: Citation_Information: Originator: Alan Rea and Robert L. Tortorelli Publication_Date: 1999 Title: Precipitation depth-duration-frequency surfaces for Oklahoma Edition: Version 1.0, July 23, 1999 Geospatial_Data_Presentation_Form: map Series_Information: Series_Name: USGS Open-File Report Issue_Identification: USGS OFR 99-463 Publication_Information: Publication_Place: Oklahoma City, Oklahoma Publisher: U.S. Geological Survey Online_Linkage: Description: Abstract: These geospatial data sets consist of surface grids of precipitation depths for seven frequencies at 12 durations used in a regional precipitation frequency analysis for Oklahoma. Eighty-four depth-duration-frequency surfaces were interpolated from precipitation-station data. The grid-cell spacing is 2,000 meters. Each depth-duration-frequency surface was interpolated using the same interpolation function and parameters. Data were used from precipitation gage stations with at least 10 years of record within Oklahoma and about 50 kilometers into bordering states. Data were analyzed for seven frequencies (expressed as recurrence intervals of 2-, 5-, 10-, 25-, 50-, 100-, and 500-years) and 12 durations (15-, 30-, and 60-minutes; 1-, 2-, 3-, 6-, 12-, and 24-hours; and 1-, 3-, and 7-days). Statistical methods were used to estimate precipitation depths for each duration-frequency at each station. These station depth-duration-frequency estimates were interpolated to produce continuous grids with grid-cell spacing of 2,000 meters. Contour lines derived from these surfaces (grids) were used to produce the maps in the "Depth-Duration Frequency of Precipitation for Oklahoma," by R.L. Tortorelli, Alan Rea, and W.H. Asquith, U.S. Geological Survey Water-Resources Investigations Report 99-4232. These geospatial data sets may be used to determine an interpolated value of depth-duration-frequency of precipitation for any point in Oklahoma. Purpose: These data sets were used to produce the maps in the Depth-Duration Frequency of Precipitation for Oklahoma (Tortorelli, Rea, and Asquith, 1999). Supplemental_Information: L-moment statistical methods were used to estimate depth-duration-frequency relations for each precipitation station. See Tortorelli, Rea, and Asquith, (1999) for discussion of the statistical methods. L-coefficient of variation and L-skew were averaged for each station with its four nearest neighbors. The values were weighted by the number of years of record at each station. The means were not averaged. The IDW function in ARC/INFO was used with an exponent of zero to average the values for each point and its four nearest neighbors. The effect was to spatially smooth the frequency distribution parameters while leaving the mean values unchanged. The frequency distribution parameters were used to calculate the depth-duration-frequency (DDF) relation for each precipitation station. The ARC/INFO GRID function, POINTINTERP (ESRI, 1997) was used to interpolate surface grids of each DDF on a 2-km cell size. The exponential smoothing option was used for POINTINTERP, with a decay radius of 50 km and a neighborhood radius of 100 km. The POINTINTERP function calculates distance-weighted averages for each grid cell of all observed values within the neighborhood radius of 100 km. The weight function is an exponential decay function that goes to 0 at the neighborhood radius of 100 km. Length-of-record weighting for the grid interpolation was accomplished by multiplying the DDF values by the number of years of record for each station, then interpolating a surface of the multiplied values using the POINTINTERP function. Then POINTINTERP was used to interpolate a surface of the years of record using the same decay and neighborhood parameters. Then for each grid cell the values of the first surface were divided by the values of the second surface. This had the effect of weighting the final surface by the period of record. The result of this length-of-record weighting is that the final interpolated surface is closer to the observed values at stations having longer periods of record than at stations with shorter periods of record. After interpolation the DDF grids were masked to include just the area of Oklahoma plus a 20-km buffer. This was done to (1) minimize the effects of poorer interpolations near the edges of the data (at 50 km outside Oklahoma), and (2) assist in interpolating depth values at the State border. Contour lines were then derived from each surface, choosing an appropriate contour interval. It is intended that the maps be used to estimate the precipitation depth values within the State. The DDF grids were checked to ensure that the DDF values increase monotonically (are continuously increasing) with increasing duration and increasing frequency. For example, (1) within the 12-hour duration, the 100-year DDF is larger than the 50-year DDF for all grid cells, and (2) within the 100-year frequency, the 24-hour DDF is larger than the 12-hour DDF for all grid cells. Only a few very small deviations from monotonically increasing DDFs were observed. All were near the edges of the grids at the 500-year frequency at durations 6-hours and above and all were outside Oklahoma. An excerpt from the Arc Macro Language (AML) program used to interpolate the surfaces follows: >/* Add items and calc products for period-of-record weighting >tables >additem sites%dur%.pat porw2yr 9 9 n 4 >additem sites%dur%.pat porw5yr 9 9 n 4 >additem sites%dur%.pat porw10yr 9 9 n 4 >additem sites%dur%.pat porw25yr 9 9 n 4 >additem sites%dur%.pat porw50yr 9 9 n 4 >additem sites%dur%.pat porw100yr 9 9 n 4 >additem sites%dur%.pat porw500yr 9 9 n 4 >sel sites%dur%.pat >calc porw2yr = yrsrec * freq2yr >calc porw5yr = yrsrec * freq5yr >calc porw10yr = yrsrec * freq10yr >calc porw25yr = yrsrec * freq25yr >calc porw50yr = yrsrec * freq50yr >calc porw100yr = yrsrec * freq100yr >calc porw500yr = yrsrec * freq500yr >quit > >/* run pointinterp() to make Depth-Duration-Frequency surfaces >/* First set cell size and snap to snap grid > >grid >setwindow -700000 1120000 190000 1640000 >setcell 2000 > >ayrs = pointinterp ( sites%dur%, yrsrec, #, EXP_SMOOTH, 50000, 0, 100000 ) > >&do freq &list 2yr 5yr 10yr 25yr 50yr 100yr 500yr > >porw%freq% = pointinterp(sites%dur%,porw%freq%,#,EXP_SMOOTH,50000,0,100000) >setmask /proj/temp1/okrain/sitemaps/okbuff20g >surf%freq% = porw%freq% / ayrs >setmask off > >&end /* of do-freq-list Related Data sets-- The precipitation stations data sets and contour data sets derived from each surface are being published with these data sets. Other References Cited-- Asquith, W.H., 1998, Depth-duration frequency of precipitation for Texas: U.S. Geological Survey Water-Resources Investigations Report 98-4044, 107 p. Environmental Systems Research Institute, Inc. (ESRI), 1997, ARC/INFO Command Reference, ARC/INFO Version 7.1.1 on-line help: Redlands, CA. Tortorelli, R.L., Rea, Alan, and Asquith, W.H., 1999, Depth-duration frequency of precipitation for Oklahoma: U.S. Geological Survey Water-Resources Investigation Report (WRIR) 99-4232, 113 p. Notes-- Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this Federal Geographic Data Committee-compliant metadata file is intended to document the data set in nonproprietary form, as well as in ARC/INFO format, this metadata file may include some ARC/INFO-specific terminology. Time_Period_of_Content: Time_Period_Information: Single_Date/Time: Calendar_Date: 1999 Currentness_Reference: Publication date Status: Progress: Complete Maintenance_and_Update_Frequency: None Planned Spatial_Domain: Bounding_Coordinates: West_Bounding_Coordinate: -104.00654778 East_Bounding_Coordinate: -93.82201908 North_Bounding_Coordinate: 37.77692744 South_Bounding_Coordinate: 32.90086456 Keywords: Theme: Theme_Keyword_Thesaurus: none Theme_Keyword: Precipitation Frequency Analysis Theme_Keyword: Precipitation Intensity Place: Place_Keyword_Thesaurus: none Place_Keyword: Oklahoma Access_Constraints: none Use_Constraints: These data are designed for regional analyses appropriate to the 2,000-meter grid cell size. Point_of_Contact: Contact_Information: Contact_Person_Primary: Contact_Person: Alan Rea Contact_Organization: U.S. Geological Survey Contact_Position: Hydrologist Contact_Address: Address_Type: mailing and physical address Address: 230 Collins Road City: Boise State_or_Province: Idaho Postal_Code: 83702 Country: USA Contact_Voice_Telephone: (208)387-1323 Contact_Facsimile_Telephone: (208)387-1372 Contact_Electronic_Mail_Address: (ahrea@usgs.gov) Data_Set_Credit: This data set was created under a cooperative agreement with the Oklahoma Department of Transportation. Native_Data_Set_Environment: SunOS, 5.5.1, sun4u UNIX ARC/INFO version 7.2.1 Data_Quality_Information: Attribute_Accuracy: Attribute_Accuracy_Report: The error associated with each surface was analyzed using methods described by Asquith (1998). The analysis was only conducted for stations within Oklahoma (statewide). The error associated with a station is defined as > E(i) = X(i) - S(i) > >where > >E(i) = error associated with precipitation depth for a duration > frequency at station i; > >X(i) = value of the precipitation depth for a duration-frequency > at the station (control point); >and >S(i) = value of the precipitation depth for a duration-frequency > at the station from the surface. The error defined is only indicative of the true error because each station was used in the surface development. An independent means to measure error is not available. The error analysis results for precipitation depth are listed in the file "table1.htm" accompanying this metadata. The table shows the comparison of the statewide mean, the standard deviation of differences between the statewide mean and each control point (station) value, and the coefficient of variation. The mean surface (contour) error, mean absolute surface (contour) error, maximum and minimum surface errors, root mean square error, and percent change from standard deviation to root mean square error for each depth-duration frequency also are listed. Each statistic is a weighted value, except for the maximum and minimum surface errors, which means the length of record of each station was considered in the computation. Maximum and minimum surface errors are listed to show the range of errors found in each depth-duration frequency of precipitation surface. The weighted mean surface error is the mean difference between values of the control points and values from the surface. Mean surface errors near zero are desirable, because this indicates how well the interpolation routine worked. This error reflects any potential bias in the surface. Root mean square error (RMSE) is analogous to the standard deviation (SD), and, therefore, the RMSE is comparable to the SD of the control points (differences between the statewide mean value and individual station values). The percent change from SD to RMSE, 100*[(RMSE ­ SD) / SD], indicates the improvement in the precipitation depth estimate by using the surfaces (or contour maps) rather than simply using the corresponding statewide mean. If the percent decrease from the statewide standard deviation to the root mean square error is not at least 15 percent (Asquith, 1998), then a contour map is not better than a single statewide mean. Percent changes from standard deviation to root mean square error for the (1) 15-minute to 60-minute durations ranged between -34.7 to -52.0 percent; (2) 1-hour to 24-hour durations ranged between -42.1 and -70.4 percent; and (3) 1-day and 7-day durations ranged between -51.8 and -70.3 percent. Therefore, the use of the surfaces (contour maps) results in more accurate estimates of the precipitation depth than simply using a statewide mean. Logical_Consistency_Report: Not applicable for raster data. Completeness_Report: For more information see Tortorelli, Rea, and Asquith, 1999. Positional_Accuracy: Horizontal_Positional_Accuracy: Horizontal_Positional_Accuracy_Report: Locations of weather stations used in the depth-duration frequency analyses were recorded to the nearest 1 minute of latitude and longitude. Lineage: Process_Step: Process_Description: First draft of metadata created by ahrea using FGDCMETA.AML ver. 1.33 07/15/99 on ARC/INFO data set /proj/temp1/okrain/cdproto/arc_data/7day/surf500y Process_Date: 19990723 Spatial_Data_Organization_Information: Direct_Spatial_Reference_Method: Raster Raster_Object_Information: Raster_Object_Type: Grid Cell Row_Count: 260 Column_Count: 445 Spatial_Reference_Information: Horizontal_Coordinate_System_Definition: Planar: Map_Projection: Map_Projection_Name: Albers Conical Equal Area Albers_Conical_Equal_Area: Standard_Parallel: 29.5 Standard_Parallel: 45.5 Longitude_of_Central_Meridian: -96 Latitude_of_Projection_Origin: 23 False_Easting: 0.00000 False_Northing: 0.00000 Planar_Coordinate_Information: Planar_Coordinate_Encoding_Method: coordinate pair Coordinate_Representation: Abscissa_Resolution: 2000.0 Ordinate_Resolution: 2000.0 Planar_Distance_Units: Meters Geodetic_Model: Horizontal_Datum_Name: North American Datum of 1983 Ellipsoid_Name: GRS1980 Semi-major_Axis: 6378206.4 Denominator_of_Flattening_Ratio: 294.98 Entity_and_Attribute_Information: Overview_Description: Entity_and_Attribute_Overview: Each depth-duration-frequency surface is identified by its name and position in the directory structure. For example, the SURF100Y data set in the 7day subdirectory contains precipitation depths for the 100-year 7-day precipitation event. All depths are in inches. Entity_and_Attribute_Detail_Citation: none Distribution_Information: Distributor: Contact_Information: Contact_Organization_Primary: Contact_Organization: U.S. Geological Survey Contact_Position: Water Webserver Team Contact_Address: Address_Type: mailing and physical address Address: 12201 Sunrise Valley Drive, MS 440 City: Reston State_or_Province: VA Postal_Code: 20192 Country: USA Contact_Voice_Telephone: (800) 426-9000 Contact_Instructions: Contact via email Contact_Electronic_Mail_Address: h2oteam@usgs.gov Distribution_Liability: Although these data have been used by the U.S. Geological Survey, U.S. Department of the Interior, no warranty expressed or implied is made by the U.S. Geological Survey as to the accuracy of the data. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the U.S. Geological Survey in the use of this data, software, or related materials. Metadata_Reference_Information: Metadata_Date: 19990723 Metadata_Review_Date: 19990901 Metadata_Contact: Contact_Information: Contact_Organization_Primary: Contact_Organization: U.S. Geological Survey Contact_Person: Alan Rea Contact_Position: Hydrologist Contact_Address: Address_Type: mailing and physical address Address: 230 Collins Road City: Boise State_or_Province: Idaho Postal_Code: 83702 Country: USA Contact_Voice_Telephone: (208)387-1323 Contact_Facsimile_Telephone: (208)387-1372 Contact_Electronic_Mail_Address: (ahrea@usgs.gov) Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata ("CSDGM version 2") Metadata_Standard_Version: FGDC-STD-001-1998 Metadata_Access_Constraints: none Metadata_Use_Constraints: none