10 Nov 2025

Spatial Analyses of Atmospheric Rivers in the Willamette River Basin of Oregon: Literature Review and Atmospheric River

Abstract: This technical note summarizes the literature review and atmospheric river (AR) detection technique data collection and initial processing activities that were performed in preparation to spatially storm type (i.e., categorize) AR extreme storm events in Oregon’s Willamette River Basin (WRB). Storm typing is performed to develop a homogeneous extreme event dataset for precipitation-frequency analyses, whose products are used to support business line (e.g., Dam and Levee Safety and Flood Risk Management) activities of the US Army Corps of Engineers (USACE). Twenty-three Atmospheric River Tracking Method Intercomparison Project (ARTMIP) Tier 1 data catalogs were collected from the US National Science Foundation’s National Center for Atmospheric Research Climate Data Gateway (Rutz et al. 2019). Each catalog models the binary presence or absence of an AR on a gridded basis, globally, at a three-hour time step from 1980 to 2016. Any ARTMIP Tier 1 catalog could effectively be selected and applied to segment AR extreme storm events for a given area by intersecting it with a prescribed precipitation dataset. However, each catalog characterizes the presence or absence of ARs differently. Hence, there exists uncertainty regarding which ARTMIP Tier 1 catalogs to select for a given practical application. This technical note addresses the uncertainty associated with ARTMIP Tier 1 catalog choice by generalizing model selection (i.e., which ARTMIP Tier 1 methods to use). Monthly climatological AR frequency was calculated throughout the WRB for each of the 23 ARTMIP Tier 1 data catalogs. Thirteen of the AR identification and tracking methods that together consistently calculated climatological AR frequency throughout the WRB were selected to form an ensemble subset. The 13-member ensemble could be used to develop AR storm type (Ralph et al. 2019) annual and seasonal maxima datasets to compute areal-precipitation-frequency estimates for the contributing drainage areas of dams in the WRB that are operated and maintained by USACE.