Precipitation intensity-duration-frequency estimates for the state of Minnesota built from dynamically downscaled climate model simulations

Flooding risk is projected to increase throughout the 21st century in the Upper Midwest of the United States due to the increasing frequency and intensity of extreme rainfall, making climate-resilient stormwater infrastructure and updated flood-management strategies increasingly important. These types of infrastructure are commonly designed using Intensity-Duration-Frequency (IDF) curves from NOAA's Atlas 14 (NA14), a resource derived from historical observations and built under the assumption of climate stationarity. While Atlas 15 is expected to address these issues at the national scale, no updated, high-resolution, non-stationary IDF product exists for the state of Minnesota, needed to support climate-resilient infrastructure design and adaptation measures in the interim. Here, we provide future IDF estimates built from dynamically downscaled simulations from 6 CMIP6 models using the Weather Research and Forecasting (WRF) model. We fit GEV distributions to annual maximum series from the high-resolution projections for a historical period (1995-2014) and three future 20-year periods (2040-2059, 2060-2079 and 2080-2099) under SSP2-4.5, SSP3-7.0 and SSP5-8.5. We provide relative changes for the raw simulations, and absolute IDF values following quantile-mapping bias correction, with uncertainty in both expressed as a median estimate followed by a "likely" range of 17th-83rd percentiles of inter-model spread. By the end of the century (2080-2099), statewide average 1-day-duration events are projected to increase by 16% (7%-26%) for a 2-year return interval (RI), 23% (11%-35%) for 10-year RI, and 35% (15%-60%) for 50-year RI under SSP3-7.0. Increases in IDF values are consistent across scenarios, durations, and RI, though spatial heterogeneity and model spread grow substantially for RI values above 50 years. These results support the updating of IDF resources and provide a state-specific dataset for stormwater infrastructure design, urban drainage, flood-risk management and climate-adaptation planning in Minnesota.