Assessing the Combined Risk of Fire and Flood on a National Scale for Sweden

Floods and wildfires are two critical hazards that impose substantial direct and indirect costs to society, including the resource needs of rescue services. Their occurrence is strongly linked to meteorological conditions, playing a fundamental role in hazard development and assessment. These hazards are notably distinguishable due to opposing weather requirements, wet conditions for floods and dry conditions for wildfires. However, certain regions are exposed to the convergence of these hazards simultaneously or in temporal proximity, demanding different levels of resources and mitigation strategies. Consequently, there is a vital need for a comprehensive combined risk assessment to enhance the effectiveness of rescue services to face such risks. This study presents an analysis for the combined risk of wildfires and floods on a national scale in Sweden over an 11-year period based on daily values on the Fire Weather Index (FWI) and river flow data, taken as proxies for the occurrence of fire and flood, respectively. The present study employed different methods to assess the joint occurrence of fire and floods including simultaneous plots of FWI and flow timeseries, scatter plots with risk categorization, and index plots combining standardized FWI and flow, offering both qualitative and quantitative insights into combined risk assessment.