Global Atmospheric River Historical Data Record: Combining AR Detection and Intensity Categorization

The U.S. National Centers for Environmental Information (NCEI) is sponsoring the development of a reanalysis-based global atmospheric river (AR) historical data record (HDR) to serve as a valuable resource for the scientific, operations-based, and decision-making communities. The AR HDR uses a novel combination of two techniques: (1) the AR scale, which broadly characterizes AR strength from 1-5 based on the peak integrated water vapor transport (IVT) and duration of AR conditions (i.e., IVT ≥ 250 kg m-1 s-1) at a given location, and (2) the tARget AR detection algorithm–a tool that uses climatological, geometric, and directional thresholds to identify ARs. Since the AR scale has no geometric criteria (and thus identifies/ranks non-AR events such as tropical cyclones, cutoff lows, and monsoons) and tARget does not provide characterization of AR strength, these two methods complement each other: tARget differentiates between ARs and other storm types, while the AR scale provides rankings. The resulting AR database is used to examine select global cases, interannual variability, long-term climatologies of global AR characteristics categorized by rank, and reanalysis-based precipitation. The results demonstrate the combined capability of tARget to identify ARs and the AR scale to subsequently characterize their intensity, such that AR-related impacts globally can be better understood. The AR HDR will be hosted by NCEI. Future work includes implementation of the HDR method in forecasts, comparison to observed hydrometeorological datasets where available such as precipitation, streamflow, and drought, and an examination of AR scale modifications in polar and mountainous regions.