MAXIMAZATION OF PRECIPITATION SEQUENCES DURING WINTERTIME IN THE COLUMBIA RIVER BASIN AND ITS ANALYSIS

Abstract

 In basins where disastrous floods are driven by long-duration processes, such as snow accumulation/melt and series of storm events, estimating maximum precipitation (MP) for not a single storm duration but long durations is necessary to estimate maximum flood. Although the model-based methodology to estimate MP for long durations was recently proposed, it is still required to better understand what characteristics of water years lead to higher increases in precipitation depths. To examine this issue, this study performed the model-based maximization of precipitation sequences during winter (Oct-Mar) of the 9 historical water years (94 Atmospheric River (AR) events) for the drainage areas of Bonneville Dam and Libby Dam in the Columbia River Basin. The storm selection based on the thresholds of Integrated Water Vapor Transport (IVT) showed that the use of CFSR resulted in selecting more AR events than the use of 20CRv2c-ensemble mean, implying the importance of reanalysis products in MP estimation. The 1996 water year showed high potential in precipitaton increase, implying that the 1996 Pacific Northwest floods could have been more disastrous. The total duration of AR events during winter in a water year showed high positive correlations (R=0.84 for Bonneville and R=0.97 for Libby) with the precipitation increase rate from historical to maximum in the long-duration precipitation depths. This study found that each AR’s trajectory may be the key to determining the increase rate in winter cumulative precipitation depths. Further studies are needed to examine how the use of different reanalysis products can affect the results and to quantify the potential in precipitation increase using AR trajectories.