The traditional method of determining design discharges for hydraulic structures in Alaska and elsewhere is to use historical data. However, Alaska now has a non-stationary climate, which means that current climate data are heterogeneous and hence trends over time prevent historical data from being used to estimate future conditions. Alaska is projected to experience major changes in extreme weather during the twenty-first century.

This project used the best available modeled climate data and associated methodologies to calculate and provide downscaled, bias corrected projections of future liquid precipitation from now until 2100 in formats and appropriate summary intervals for the Department of Transportation and Public Facilities (DOT&PF) direct use in planning and design efforts and associated calculations. To facilitate direct integration into the DOT&PF’s operations, the projected precipitation data products closely follow the format of the NOAA ATLAS 14 precipitation frequency estimates, providing outputs across the entire state of Alaska for a range of precipitations durations and probability-based return intervals.

This project does not replicate all functions of the current NOAA ATLAS 14 website, although the online tools are very similar, to aid in familiarity and ease of use. It instead focuses on providing efficient access to datasets that concorporate and interpret the best available climate information and models. It includes six complete data options – two different models for each of three different future time periods — thus representing the range of future projections associated with climate change.

Data outputs show substantial increases in projected precipitation across regions, durations, return intervals, and future time periods. These changes have important ramifications for engineering and hydrological design in Alaska, now and in coming decades.