Climate Change Adjustments for Intensity-Duration-Frequency Extreme Precipitation Values

Anthropogenically-forced global warming is expected to cause increases in extreme precipitation. This is one of climate science’s more confident projections, based on many global climate model simulations and fundamental physical considerations, specifically the sensitive dependence of saturation water vapor pressure on temperature. Much societal infrastructure that must deal with runoff has long lifetimes exceeding 50 years. In that time frame, it is highly likely that such infrastructure will experience increased intensity and frequency of extreme precipitation events. If such infrastructure is built with extreme precipitation design values based solely on historical data, it will not perform according to expectations, leading to reduced societal climate resilience.

A project is underway to incorporate the potential impacts of anthropogenically-forced changes in climate into Intensity-Duration-Frequency design values. This project is examining two aspects of changes in the climate system: (1) increases in atmospheric water vapor, and (2) changes in the frequency and intensity of weather systems that cause extreme precipitation. The former aspect will cause increases everywhere while the latter may either reinforce or partially negate the water vapor increases. Weather systems being investigated include the fronts and low pressure centers associated with extratropical cyclones, tropical cyclones, and the North American Monsoon system.

A comprehensive historical trend analysis for the U.S. indicates that there have been substantial regional variations in trends with large increases in the northeastern half of the U.S. while small changes have been observed in the southwest. Largest upward trends are observed for the rarest events.

Progress on historical and future changes in weather systems will be reported.