Natural Resources

Efficiently and responsibly managing and protecting our water and land resources for the sustainability, health, safety, and economic benefit of the State of Arkansas

Probable Maximum Precipitation Study

The 2019 Probable Maximum Precipitation (PMP) Study was implemented as a peer-reviewed investigation, using existing methodologies and science to create updated data, tools, and procedures for estimating extreme precipitation depth, area, and duration relationships for the regional area including Arkansas, Louisiana, and Mississippi. Historically, PMP rainfall depths for spillway design were estimated using Hydrometeorological Reports [HMRs] 51, 52, and 55A provided by the National Oceanic and Atmospheric Administration (NOAA).  

These HMRs are increasingly viewed as outdated and their use in dam safety regulation has become increasingly difficult to defend to dam owners and to elected officials. Like other states, Arkansas, Louisiana, and Mississippi identified and set as a priority updating extreme precipitation estimates for use in evaluating spillway adequacy. Due to the similarities in geography and meteorology between the three states, a cooperative, regional approach was proposed. 

The ultimate goal of the PMP Study was creation of updated, broadly accepted GIS-based tool for estimating PMP precipitation depth, area, and duration relationships for individual basins within the Arkansas/Louisiana/ Mississippi region.  This tool – the PMP Evaluation Tool – is available for use by the engineering and dam safety community. 

PMP Evaluation Tool

The PMP Evaluation Tool uses a Python-based script designed to run within the ArcGIS environment. ESRI’s ArcGIS Desktop Basic software, version 1.4 or later, is required to run the tool, and it is recommended that the user have a basic familiarity with the operation of this software. The tool provides gridded PMP values at a spatial resolution of 90 arc-seconds (equivalent to .025 x .025 decimal degrees) for a user-designated drainage basin or area at user-specified durations, in addition to basin average PMP depths and temporally distributed accumulations.

By clicking HERE, users will be able to download the PMP Evaluation Tool as a compressed folder.  Also available HERE and within the compressed folder is the GIS PMP Tool Documentation

Questions regarding use of this tool can be directed to the Whit Montague, Engineer Supervisor at

PMP Evaluation Tool Downloads