Understanding compound hazards from a weather system perspective

Natural hazards such as extreme wind, rainfall and ocean waves can have severe impacts on built and natural environments, contributing to the occurrence of disastrous events in some cases. These hazards are often caused by weather systems such as cyclones, fronts and thunderstorms. Previous studies typically examine one type of hazard and/or one type of weather system, with some studies in recent years starting to focus on compound hazards. Here we systematically examine compound hazards (extreme precipitation, extreme wind gusts, and extreme waves) from a weather system typology perspective. Cyclones and fronts are identified automatically from ERA-Interim reanalysis data, and thunderstorm events are based on lightning observations from 2005 to 2015, defining the study period. Relationships are examined over this period between the different compound hazard types and the weather system types, globally for different seasons. Most of the individual and compound hazards are most likely to be associated with the front-only or cyclone and front weather system types, while in the tropics, most hazards are strongly associated with the thunderstorm-only type. Despite being less frequent than the double weather system types, the triple weather system type shows comparable importance for many of the hazards, and especially the triple hazard. Individual case studies are examined using this compound event framework. It is intended that a greater understanding of compound hazards and the weather systems that cause them in regions throughout the world will help lead to improved preparedness and disaster risk reduction, given the importance of this for our rapidly changing world.