NOAA’s Atlas 15 Precipitation Frequency Estimates

Federal, State, and local standards and regulations are in place to protect Americans from flooding caused by extreme weather events. Nationwide Engineers use the Precipitation Frequency Duration (PFD) curves (currently at Atlas 14) to plan and design infrastructure for water control and management, and other developments such as roadways, buildings, restoration areas, etc., in accordance with such regulations.

Atlas14’s PFD curves help to estimate flood risks, based on extreme precipitation observations. Likewise, Atlas15’s curves/estimations will be the authoritative source for precipitation frequency information across the United States. In this case, the non-stationarity nature of the extreme precipitation events would be incorporated in the statistical approach used for the estimations and spatially continuous coverage, over the entire United States, will be provided¹.

An Atlas15 pilot project covering the state of Montana was released by September 2024². The deliverables included Precipitation Frequency (PF) estimates and the corresponding upper and lower bounds of 90% confidence intervals for a subset of durations and frequencies. The PF was estimated by fitting the Generalized Extreme Value (GEV) distribution to quality-controlled unconstrained annual maximum series (AMS) data at individual stations. The regional Maximum Likelihood Estimation (MLE) method was used to incorporate temporal and spatial covariates.

Our work is part of the efforts of the NOAA National Weather Service (NWS) Office of Water Prediction (OWP) to account for expected climate variability through the year 2100, so that new infrastructures and developments hold the desired level of climate-resiliency for our communities.

1. Atlas 15 info page (noaa.gov)
2. noaa_atlas15_pilot_technical_report.pdf (weather.gov)