Compound Events in a Changing Climate

Traditional approaches to understanding the risks associated with climate change have focused on a single climate variable or indicator at a time e.g. changes in the frequency of heatwaves or the intensity of droughts. However, a growing body of knowledge and experience recognizes that the additional stress created by the interactions between processes, jointly referred to as compound
events, can challenge communities in ways potentially exceeding the simple sum of the individual processes. Interactions between drought and heatwaves, for example, can greatly increase the risk of wildfires. Storm surges and elevated water levels can force the closure of sluices in river systems, exacerbating the risk of river flooding if accompanied by heavy rain. Still and dry periods can severely impact the energy supply by simultaneously limiting the production of both wind and hydro-energy. The processes related to imposing compound events tend to occur at a range of spatio-temporal scales and analogue events have possibly only occurred prior to when routine observational records have
started. This adds substantial challenges into the process of study design and analyses. Improving our understanding of the current and future likelihood of such compound events is essential to adapting our society to the challenges of a changing climate. In this study, we will assess the risks to certain types of meteorologically-driven compound events now and in the future. Given the large range of potential events that can be considered, it is first necessary to identify a subset of events to focus on: this selection process will be supported by surveying existing knowledge and events both in Denmark and internationally.
Dialogues with stakeholders in Danish society may also be used, together with the development of storyline approaches. Methodologies to quantify the most relevant and interesting events will then be developed, tested, and - if applicable - applied to Denmark as the central case study region. Finally, the method(s) will be applied broadly to consider future changes in these events in a broader perspective.The work will take place in connection with DMI’s Klimaatlas. Klimaatlas provides state of the art projections of the regional and local climate of Denmark down to the level of local authorities (“kommuner”), where it is used as a central tool in, among other, climate adaptation planning. The network of stakeholders associated with Klimaatlas will play a key role in helping shape and identify the type of events to focus on. Furthermore, the results produced in this work will form a necessary background for a direct use in Klimaatlas, aiming to produce future climate projections in high geographical detail to guide the planning of Danish authorities around compound events.