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Addressing the challenge of compound events, multi-risk modelling and cross-risk assessment methods (co-organized)
Convener: Jakob Zscheischler  | Co-Conveners: Marleen de Ruiter , Seth Westra , Xuebin Zhang , Bart van den Hurk , Olivia Romppainen-Martius , Philip Ward , Michael Leonard , Thomas Wahl , Gabriele Hegerl , Lisa Alexander , robert vautard , Sonia Seneviratne , James Daniell 
 / Fri, 28 Apr, 15:30–17:00
 / Attendance Fri, 28 Apr, 17:30–19:00

This session focuses on modeling compound events as well as multi- and cross-risk assessments. Hazards such as floods, wildfires, heatwaves and droughts often result from a combination of interacting physical processes that take place across a wide range of spatial and temporal scales. The combination of physical processes leading to an impact is referred to as a “compound event". Compound events have been identified as an important challenge by the World Climate Research Programme (WCRP) ‘Grand Challenge’ on extreme events.

In this context, managing the impact of natural hazards is also important. Various methods have been developed to assess risks related to natural hazards by combining indicators related to the hazard, exposure and vulnerability. Such assessments are usually developed and performed separately for different hazards, despite using similar data and approaches, and for areas that may face multiple hazard types. Compared to single-risk modeling, there are several factors complicating multi-risk modeling, such as: interactions between different hazards (i.e., compounding events); cascading effects; and substantial differences in risk assessment methodologies between different hazards.

The purpose of this session is to bring together scientists and studies from a wide range of discipline areas to illustrate how including multiple perspectives improves risk assessments. Specifically, papers are sought to address the following themes:

• Document: Which climate variables need to be assessed jointly in order to address related impacts and characterise the relevant class of compound event? How much is currently known about the dependence between these variables? Are the observations sufficient to underpin the assessment of these variables and their dependencies in the historical climate? What are the state-of-the-art multi-risk assessment methods and tools used?

• Understand: What are the processes that lead to dependence between the identified climate variables? What is the role of spatial and temporal scale at which the processes are analyzed in influencing the strength of dependence between variables? How are these processes expected to change as a result of anthropogenic climate change? What can risk assessments learn from methodologies from other disciplines and in what ways can the difficulties in multi-risk modeling be addressed and improved?

• Simulate: Are models able to reliably simulate the dependence between climate variables and how they might change in a future climate? What methods are available to evaluate the capacity of models to simulate an appropriate level of dependence between variables? What methods are available to assess the interaction between different hazards?

• Attribute: To what extent are historical and/or projected changes in the identified compound events attributable to particular causes? Are the available modeling tools appropriate to enable attribution of compound events or classes of events? Does forcing change the physical mechanisms involved in compound events, leading to stronger or weaker connections?