U.S. Department of the Interior U.S. Geological Survey Prepared in cooperation with the Arkansas Natural Resources Commission Mean Annual, Seasonal, and Monthly Precipitation and Runoff in Arkansas, 1951-2011 By Aaron L. Pugh and Drew A. Westerman Scientific Investigations Report 2014-5006 SUGGESTED CITATION: Pugh, A.L., and Westerman, D.A., 2014, Mean annual, seasonal, and monthly precipitation and runoff in Arkansas, 1951-2011: U.S. Geological Survey Scientific Investigations Report 2014-5006, 40 p., http://dx.doi.org/10.3133/sir20145006. ABSTRACT: This report describes long-term annual, seasonal, and monthly means for precipitation and runoff in Arkansas for the period from 1951 through 2011. Precipitation means were estimated using data from the Parameter-elevation Regressions on Independent Slopes Model database; while total runoff, groundwater runoff, and surface runoff means were estimated using data from 123 active and inactive U.S. Geological Survey continuous-record streamflow-gaging stations located in Arkansas and surrounding States. Annual precipitation in Arkansas for the period from 1951 through 2011 had a mean of 49.8 inches. Of the six physiographic sections in Arkansas, the Ouachita Mountains had the largest mean annual precipitation at 53.0 inches, while the Springfield-Salem plateaus had the smallest mean annual precipitation at 45.5 inches. The mean annual total runoff for Arkansas was 17.8 inches. The Ouachita Mountains had the largest mean annual total runoff at 20.4 inches, while the Springfield-Salem plateaus had the smallest mean annual total runoff at 15.0 inches. Runoff is diminished during the dry season, which is attributed to increased losses from evapotranspiration, consumptive uses including irrigation, and increased withdrawals for public and private water supplies. The decline in runoff during the dry season is observed across the State in all physiographic sections. Spatial results for precipitation and runoff are presented in a series of maps that are available for download from the publication Web page in georeferenced raster formats. CONTENTS: 00KmlReadme.txt AR_Mean_Prcp_Rnof_1951-2011.kmz DATA UNCERTAINTY: The precipitation data used for this study were derived from the Parameter-elevation Regressions on Independent Slopes Model (PRISM; PRISM Climate Group, 2013), which is spatially gridded and available on a monthly and annual time step for the period of interest. PRISM data include the interpolation of point data from precipitation monitoring stations, the pattern and effects of mountainous terrain, and other climatic parameters influencing precipitation in the development of a continuous grid for the United States (PRISM Climate Group, 2013). The precipitation data were distributed across Arkansas at a cell size resolution of approximately 2.5 miles (mi) on a side. Annual and seasonal values were produced by summing the appropriate monthly grids. The runoff maps in this report were developed from nine raster surfaces interpolated using a Simple Kriging model with 19 input data points within a spherical radius and with a cell size resolution of approximately 1.4 mi on a side. To quantify the accuracy of the Simple Kriging model used to generate the nine runoff maps, the root mean squared error (RMSE) was calculated for each model. The RMSE provides an indication of how closely a model predicts the measured value (esri, 2010). The smaller the RMSE value, the more closely the model prediction matches the measured values. Listed below are the RMSE values associated with each of the nine runoff maps: Mean annual total runoff: 0.70 inches Mean wet season total runoff: 2.21 inches Mean dry season total runoff: 1.07 inches Mean annual groundwater runoff: 1.38 inches Mean wet season groundwater runoff: 0.90 inches Mean dry season groundwater runoff: 0.57 inches Mean annual surface runoff: 1.47 inches Mean wet season surface runoff: 0.49 inches Mean dry season surface runoff: 0.59 inches INSTRUCTIONS AND DOCUMENTATION FOR U.S. GEOLOGICAL SURVEY SCIENTIFIC INVESTIGATIONS REPORT 2014-5006 To access the data: The data files can be downloaded via the web from http://dx.doi.org/10.3133/sir20145006. The main product is a Portable Document Format (.pdf) report which requires Adobe Acrobat for viewing. Acrobat software runs on a variety of systems, and is available for download free of charge from Adobe at http://www.adobe.com. To access the .kmz files in this report, download and install Google Earth free of charge at http://www.google.com/earth/index.htm. Launch Google Earth, click the file menu and choose open. Locate and select the .kmz file on your computer. References to non-U.S. Department of the Interior (DOI) products do not constitute an endorsement by the DOI. By viewing the Google Maps API on this web site the user agrees to these terms(terms found at: http://code.google.com/apis/maps/terms.html) of Service set forth by Google. Software Recommended: Adobe Acrobat (6.x, 7.x, or 8.x), or Adobe Acrobat Pro (6.x, 7.x, or 8.x), or the free Adobe Reader (8.x or 10.x), 10.x is preferred. ArcGIS 10.0 preferred, older versions may also work.