A National Extreme Storm Database for Infrastructure Assessments

Hydrologic engineers rely on precipitation data from historical extreme storm rainfall events when calibrating hydrologic models, for frequency analysis and risk assessments, and in estimating the Probable Maximum Precipitation (PMP). The availability of extreme storm rainfall data, encompassing the largest-magnitude events in space and time, is critical to risk-informed assessments for critical infrastructure. Despite the identification of key extreme storms and various repositories of rainfall observations, publically available gridded precipitation data that is formatted for use in hydrologic models such as HEC-HMS remains limited. A goal of the U.S. Army Corps of Engineers (USACE) is to develop and improve an extreme storm database to support ongoing and future USACE risk-informed dam and levee safety studies, and for evaluating potential improvements to flood risk management operations.

An effort was initiated in USACE in early 2010 to begin the process of creating a database of extreme storm events. The initial work was focused on digitizing Pertinent Data Sheets from the Storm Rainfall in the United States published though 1973. These volumes contained Depth-Area-Duration (DAD) tables and a limited number of mass curves for high precipitation storms that were analyzed by USACE and the U.S. Weather Bureau. For regional purposes, radar data was also included to contemporary storms observed in the Missouri River basin as well. The need for a database that captured extreme events across the nation was identified along with a desire to have the data formatted such that it could be easily incorporated into hydrologic models for studies of critical infrastructure.

Recognizing the limitation of the legacy database, USACE began the process in 2017 of developing an improved database for the nation. The updated database is designed to serve as a repository of extreme precipitation data that is readily accessible, formatted to seamlessly fit into hydrologic models, and encompasses the most critical events that impact project designs for dam and levee safety. The current infrastructure is building upon developed gridded, hourly precipitation files created through HEC-MetVue for recent and ongoing hydrologic studies by USACE. This effort includes post-HMR events as well as the digitization of historic isohyetal maps into DSS and ASCII files.

Long-term development of the USACE database will involve completing the digitization and uploading of the Pertinent Data Sheets from the Storm Rainfall in the United States along with the relevant DAD tables. As these are eventually analyzed and converted into gridded, hourly precipitation data, the effort also includes storage of radar and gage data from some of the more recent extreme precipitation events. The meteorological data recorded from Hurricane Sandy in 2012, Hurricane Harvey in 2017, and other recent events can be added to the database and placed in proper longer-term historical context to evaluate potential impacts to infrastructure critical to USACE dam and levee safety.

The database will be designed for public access via web interface, with map-based searching and querying capabilities, storage of multiple analyses per event, and community contributions. Finally, the architecture of the updated database is designed to be flexible enough to store a variety of meteorological data (temperature profiles, snow water equivalent observations, etc.) that are also used as inputs into many hydrologic models. HEC-MetVue, recently released to the public, will eventually have the capability to download storm data directly from the database for visualization and analysis prior to inclusion in a particular hydrologic model. The end result will be the availability of key precipitation data for critical infrastructure to aid in the risk management process, thereby ensuring safety and efficiency in the use of public funding.