Compound Events

Conveners: Alexandre Ramos & Nina Ridder

Compound weather and climate events refer to the combination of multiple climate drivers that contributes to societal or environmental risk. Many major climate-related disasters are typically a result of a Compound Event. During such events, multiple weather and climate drivers come together and surpass the coping capacity of the underlying systems.

For instance, three consecutive years of drought, combined with high wind speeds and low relative humidity contributed to the unprecedented extent and intensity of the bushfires during Australia’s Black Summer 2019/20. Within a few months tens of millions of hectares of land were lost to the fires in four different states and territories and more than three billion animals were killed or displaced with some species assumed to be lost permanently. Additionally, to the fires, thick smoke covered major cities in southeast Australia causing hazardous air pollution which increased fatalities from 33 direct deaths to over a hundred. The estimated total cost of the event lies in the billions.”.

Even though our understanding of climate extremes and associated impacts is continuously improving, events that break the coping capacity of social and environmental systems often surprise us. This is because most current risk estimates underestimate the risks associated with correlated compound drivers.

Over the last few years, the notion of compound events has been introduced in the Atmospheric River research: e.g. The role of atmospheric rivers in compound events consisting of heavy precipitation and high storm surges along the Dutch coast (Ridder et al., 2018) or the study by (Fish et al.,2019) about Atmospheric River Families.