Projected Changes in Atmospheric Rivers in Response to Greenhouse Warming
Date:
Understanding the future changes in atmospheric river (AR) characteristics is a priority due to its role in the mean water vapor transport across midlatitudes, mean precipitation, and extreme events. Most of the AR detection algorithms use a threshold on physical variables like integrated water vapor transport (IVT) or water vapor content (WV). Although these threshold-based methods work well in the present-day (PD) climate, extending them to scenarios with large changes in IVT and WV influences our conclusions on future changes in ARs. Here, we introduce a threshold-free AR detection method, Scalable Feature Extraction and Tracking (SCAFET) which is based on the local geometric shape of the IVT magnitude. The new method is applied to century-long ultra-high resolution simulations (0.250 resolution in the atmospheric component and 0.100 resolution in the ocean component) of PD climate and greenhouse warming conditions. The future changes in AR geometry, dynamics, and thermodynamics are discussed with particular emphasis on how they deviate from the previous studies. In terms of the area and frequency of AR structures, unlike the other detection methods, our new method does not show a huge increase. However, we observe a significant poleward shift in AR frequency and an intensification of IVT within ARs. The changes in precipitation within ARs are influenced by the increased WV and reduced lower tropospheric wind speeds in a warmer world. We confirmed that the AR-induced precipitation as well as the mechanism of future AR changes are dependent on the algorithm used, in particular, the type of threshold employed.