Impacts of Rossby Wave Packets and Atmospheric Rivers on Meteorological Drought in the Continental United States

Drought is among the costliest natural disasters and its spatiotemporal scales are larger than those of other water-related disasters. However, our understanding of drought causative mechanisms is less than complete, inhibiting accurate drought forecasting and early warning. While sea surface temperature teleconnection governs the 10%-60% precipitation variability at intra-seasonal to multiannual scales, some of the unexplained variability can be understood by internal atmospheric variability, represented by Rossby wave packets (RWPs), and implications of atmospheric rivers (ARs). The amplitude and phase speed of the recurrent RWPs (RRWPs) and the atmospheric river index developed in this study were used to analyze the impacts of RWPs and ARs on droughts detected by three-dimensional drought clustering algorithms for the continental U.S. during 1951-2015. The occurrence of RRWPs raised the likelihood of the occurrence of more severe drought than did the non-occurrence of RRWPs. The increase in the occurrence of RRWPs with low phase speed escalated drought severity, area, and duration. Furthermore, the drying ARs affected drought by increasing the severity and area of extreme droughts. We measured the level of contributions of RRWPs and ARs to extreme drought occurrences. The drying ARs contributed more to extreme droughts than did RRWPs. However, the co-occurrence of ARs and RRWPs contributed more than did each individually. Our findings of the implications of RRWPs and ARs on drought characteristics offer the potential to improve our understanding of drought causative mechanisms that can enhance the proactive drought mitigation measures.

Automated summary

The study highlights the significant impacts of atmospheric variability, specifically RRWPs and ARs, on drought occurrences. RRWPs increase the likelihood and severity of drought, while drying ARs contribute to extreme droughts. The co-occurrence of ARs and RRWPs has a greater impact on extreme droughts than either individually. These findings offer potential for improving drought mitigation measures.