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Moisture transport within atmospheric rivers is driven by a complex combination of processes, including the convergence of moisture from different sources, which change over the atmospheric river's life cycle. The water vapor budget (WVB) within an atmospheric river enables us to understand moisture sources and sinks (horizontal flux, evaporation, and precipitation). Here, we applied our new WVB approach throughout the life cycle of the exceptional atmospheric river associated with Storm Dennis, which led to record-breaking precipitation on 15 February 2020. We used the WRF model to simulate the event and performed two sets of sensitivity experiments: one reducing tropical moisture and the other modifying ocean evaporation to assess how these two main moisture sources affect the water vapor balance within the atmospheric river. We analyzed changes in the atmospheric river, cyclone, and associated precipitation at landfall in the sensitivity experiments. In the Dennis case study, tropical moisture played a prominent role in the early stages of the atmospheric river, whereas ocean evaporation became critical later. Additionally, the reduction of evaporation and also of tropical moisture is related to a decrease in precipitation over Europe. This study offers a new approach to understanding the evolution of atmospheric rivers and highlights the importance of different moisture processes. It provides a case study that helps unravel feedback mechanisms and the impact of different perturbations on the water vapor balance of atmospheric rivers.

The explosive development of extratropical cyclones and atmospheric rivers plays a crucial role in driving extreme weather in the mid-latitudes, such as compound windstorm–flood events. Although both explosive cyclones and atmospheric rivers are well understood and their relationship has been studied previously, there is still a gap in our understanding of how a warmer climate may affect their concurrence. Here, we focus on evaluating the current climatology and assessing changes in the future concurrence between atmospheric rivers and explosive cyclones in the North Atlantic. To accomplish this, we independently detect and track atmospheric rivers and extratropical cyclones and study their concurrence in both ERA5 reanalysis and CMIP6 historical and future climate simulations. In agreement with the literature, atmospheric rivers are more often detected in the vicinity of explosive cyclones than non-explosive cyclones in all datasets, and the atmospheric river intensity increases in all the future scenarios analysed. Furthermore, we find that explosive cyclones associated with atmospheric rivers tend to be longer lasting and deeper than those without. Notably, we identify a significant and systematic future increase in the cyclones and atmospheric river concurrences. Finally, under the high-emission scenario, the explosive cyclone and atmospheric river concurrences show an increase and model agreement over western Europe. As such, our work provides a novel statistical relation between explosive cyclones and atmospheric rivers in CMIP6 climate projections and a characterization of their joint changes in intensity and location.