Next-Generation Intensity-Duration-Frequency Curves for Hydrologic Design in Snow-Dominated Environments

There is a renewed focus on the design of infrastructure resilient to extreme hydrometeorological events. While precipitation-based intensity-duration-frequency (IDF) curves are commonly used as part of infrastructure design, a large percentage of peak runoff events in snow-dominated regions are caused by snowmelt, particularly during rain-on-snow (ROS) events. In these regions, precipitation-based IDF curves may lead to substantial overestimation/underestimation of design basis events and subsequent overdesign/underdesign of infrastructure. To overcome this deficiency, we proposed next-generation IDF (NG-IDF) curves, which characterize the actual water reaching the land surface. We compared NG-IDF curves to standard precipitation-based IDF curves for estimates of extreme events at 376 Snowpack Telemetry (SNOTEL) stations across the western United States that each had at least 30 years of high-quality records. We found standard precipitation-based IDF curves at 45% of the stations were subject to underdesign, many with significant underestimation of 100 year extreme events, for which the precipitation-based IDF curves can underestimate water potentially available for runoff by as much as 125% due to snowmelt and ROS events. The regions with the greatest potential for underdesign were in the Pacific Northwest, the Sierra Nevada Mountains, and the Middle and Southern Rockies. We also found the potential for overdesign at 20% of the stations, primarily in the Middle Rockies and Arizona mountains. These results demonstrate the need to consider snow processes in the development of IDF curves, and they suggest use of the more robust NG-IDF curves for hydrologic design in snow-dominated environments. Plain Language Summary Recent natural disasters highlight the need for proper hydrologic design of infrastructure to accommodate extreme flood events. Hydraulic structures such as flood drainage systems are typically designed to convey a storm of a given duration and frequency of occurrence (e.g., the 100 year, 24 h storm event). These events are characterized by curves of a given frequency showing the relationship between precipitation intensity and duration (i.e., IDF curves). In locations with significant snowfall, standard precipitation-based IDF curves fail to capture the snowmelt and rain-on-snow events which may lead to substantial overestimation/underestimation of design basis events used for infrastructure. This study proposed next-generation IDF (NG-IDF) curves to overcome this deficiency. We used observed daily precipitation and changes in snow water equivalent at 376 Snowpack Telemetry (SNOTEL) stations to construct and compare standard precipitation and NG-IDF curves for estimates of extreme events across the western United States. Standard precipitation-based IDF curves were subject to underdesign at 45% of the stations in the Pacific Northwest, the Sierra Nevada Mountains, and the Middle and Southern Rockies. Underestimation of 100 year, 24 h events can be as much as 125%. These results suggest use of the more robust NG-IDF curves for hydrologic design in snow-dominated environments.