Impact of Non-stationary Climate Conditions on Extreme Precipitation Frequency Estimates Needed for Engineering Design

Since the early 2000s, the National Weather Service's Hydrometeorological Design Studies Center has been updating estimates for the United States and U.S. affiliated territories, and publishing them in NOAA Atlas 14, Precipitation-Frequency Atlas of the United States. NOAA Atlas 14 precipitation frequency estimates serve as the de-facto standards for a wide variety of design and planning activities under federal, state, and local regulation. The current NOAA Atlas 14 frequency analysis method cannot be generalized to incorporate non-stationarity. As such, it may not be the most suitable in the presence of non-stationary climate conditions. In an attempt to better understand the potential impact of climate change on estimates at local scales so that designers of future infrastructure will use appropriate design standards, the HDSC surveyed the state of the art methodologies in this area and conducted a pilot project to examine the viability of different approaches for use in NOAA Atlas 14. A range of non-stationary models, from the simplest one with a single distribution parameter linearly varying with time to complex models with different types of non-linear trends in all distribution parameters were investigated. Preliminary results of this analysis will be presented in the meeting.