Natural hazards pose significant risks to people and assets in many regions of the world. Quantifying associated risks is crucial for many applications such as adaptation option appraisal and insurance pricing. However, traditional risk assessment approaches have focused on the impacts of single hazards, ignoring the effects of multi-hazard risks and potentially leading to underestimations or overestimations of risks. In this work, we present a framework for modelling multi-hazard risks globally in a consistent way, considering hazards, exposures, vulnerabilities, and assumptions on recovery. We illustrate the approach using river floods and tropical cyclones impacting people and physical assets on a global scale in a changing climate. To ensure physical consistency, we combine single hazard models that were driven by the same climate model realizations. Our results show that incorporating common physical drivers and recovery considerably alters the multi-hazard risk. This framework is implemented in the open-source climate risk assessment platform CLIMADA and can be applied to various hazards and exposures, providing a more comprehensive approach to risk management than conventional methods.

<p>Wildfires are devastating events destroying large parts of physical assets exposed to them in many regions of the world. Therefore, a high-resolution hazard model is needed to accurately assess socio-economic impacts caused by wildfires. Moreover, a probabilistic representation of the hazard covering the range and likelihood of possible wildfire events under certain conditions allows for a more comprehensive risk assessment. This is crucial for many applications, among others the prioritization of adaptation measures and the pricing of insurance.</p><p>We determine burning probabilities based on MODIS hotspots and a set of predictors (weather variables, geography, land use) by using a country-specific machine learning model based on the efficient tree boosting system XGBoost. Subsequently, stochastic wildfire events are generated on the basis of these burning probabilities.</p><p>Lastly, the open-source climate risk assessment platform CLIMADA is used to compute socio-economic impacts as the combination of the newly developed hazard, an exposure and a vulnerability. The used exposure LitPop spatially distributes macroeconomic indicators (e.g. produced capital) as a function of night light intensity and population density. The vulnerability is represented by an impact function that was calibrated on historic fire damage data. Combining the stochastic impacts with their respective probabilities results in a globally consistent country-specific model of wildfire risk to physical assets.</p>

<p>Extreme weather events are among the most destructive natural hazards, affecting a large number of people and causing significant monetary damage globally each year. The impact of these events is increasing due to climate change and socio-economic development. While traditional approaches to risk assessment have focused on the impacts of single hazards, the combined risk of multiple hazards may be different from their sum. Their spatial and temporal co-occurrence may also be influenced by climate change. In this study, we develop a framework for modelling the combined risk of multiple climatic hazards, where risk is defined as the combination of hazard, exposure and vulnerability. We illustrate this method based on globally consistent river floods and tropical cyclones and their impacts on both population and assets. Both hazards are driven by global climate models to investigate their risk at current and future levels of warming. The combined impacts are evaluated by aggregating single hazard models on an event basis, where events are driven by the same climate model outputs. This allows us to not only consider the average annual impact, but also for example to assess combined extreme events or return periods. Additionally, spatially and temporally compounding events can be analysed. This framework is implemented in the open-source climate risk platform CLIMADA and can be applied to different climate risks, providing a more comprehensive approach to understanding and managing the risks posed by extreme weather events in a changing climate.</p>