Tropical Cyclones

Tropical cyclones are among the most destructive weather phenomena. Coastal regions and islands are particularly exposed as they are affected not only by the direct impact of a storm, but also by the secondary hazards, such as storm surges and pounding waves.

The intensity of a storm rapidly decreases as it moves inland because of the friction increase due to the roughness of the Earth’s surface and reduction in the supply of energy (primarily from water vapour) to the storm system. Orographic effects can also lead to high amounts of rainfall, which in turn can result in severe flooding, producing multi-billion dollar losses in populated regions with high GDP.

Current Hazard Analysis of Tropical Cyclone

The current (present day) hazard analysis of Tropical Cyclone is based on Munich Re’s Tropical Cyclone zoning in NATHAN, which uses the following variables for modelling:

• Forward wind
• Maximum wind speed
• Minimum central pressure
• Radius of maximum wind speeds
• Track of the centre (“eye”) in 3- to 6-hourly intervals (in exceptional cases, 12-hourly intervals)

The wind fields of all historical windstorms were simulated and superimposed in a grid network with a mesh size of 0.1 x 0.1 degrees of geographical longitude and latitude. By means of a frequency analysis for each grid coordinate, the maximum wind speed to be expected (probable maximum intensity with an average exceedance probability of 10% in 10 years) was derived for the return period of 100 years. The hazard zoning is represented by a five-level scale based on the Saffir-Simpson scale, multiplied by a gust factor of 1.2.

Tropical Cyclone Projections

The Tropical Cyclone projections are based on published model run results of the High-Resolution Forecast-Oriented Low Ocean Resolution (HiFLOR) model at the NOAA Geophysical Fluid Dynamics Laboratory (GFDL). The HiFLOR model allows the user to assess how climate change will alter the frequency and intensity of tropical cyclones. The scientific results are used for remodeling the NATHAN hazard zones, represented by the five-level scale for the probable maximum intensity with an exceedance probability of 10% in 10 years (equivalent to return period of 100 years). The future projections are available for the scenarios RCP 4.5 and 8.5 for the projection years 2030, 2050, and 2100.

Munich Re’s NATHAN current river flood hazard data (provided by JBA Risk Management) offers state-of-the-art flood hazard information (with a 30m horizontal resolution), available on a global scale.

The global flood maps are constantly improved and are a market standard. They are based on bare-earth digital terrain data and a consistent worldwide digital surface model. The river flood hazard is represented by three return period zones, ranging from Zone 0 (areas of minimal flood risk) to Zone 100 (100 year return period of river flood).

Flood zone Description of flood zones

Flood protection systems are defence structures to reduce the flooding to areas and properties. Globally, the quality of defence information and the structures themselves is highly variable. Hence, there is value in considering the undefended river flood hazard in order to keep global consistency. Munich Re provides both defended and undefended river flood hazard information. Information on the flood defences’ standard of protection (SoP) is also available.

The flood projections follow a hybrid method using the output from the latest high-resolution CMIP5 global climate model runs and global land surface models to estimate changes in peak water runoff at hydrological basin resolution. These changes in peak runoff are then used to scale current river flood maps, using flood depth data from JBA Risk Management. The projections are available for two emission scenarios (RCP4.5 and RCP8.5) for the projection years 2030, 2050, and 2100.

Munich Re’s NATHAN current river flood hazard data (provided by JBA Risk Management) offers state-of-the-art flood hazard information (with a 30m horizontal resolution), available on a global scale.

The global flood maps are constantly improved and are a market standard. They are based on bare-earth digital terrain data and a consistent worldwide digital surface model. The river flood hazard is represented by three return period zones, ranging from Zone 0 (areas of minimal flood risk) to Zone 100 (100 year return period of river flood) and zone 50 (50 year return period of river flood).

Flood zone Description of flood zones

Flood protection systems are defence structures to reduce the flooding to areas and properties. Globally, the quality of defence information and the structures themselves is highly variable. Hence, there is value in considering the undefended river flood hazard in order to keep global consistency. Munich Re provides both defended and undefended river flood hazard information. Information on the flood defences’ standard of protection (SoP) is also available.

The flood projections follow a hybrid method using the output from the latest high-resolution CMIP5 global climate model runs and global land surface models to estimate changes in peak water runoff at hydrological basin resolution. These changes in peak runoff are then used to scale current river flood maps, using flood depth data from JBA Risk Management. The projections are available for two emission scenarios (RCP4.5 and RCP8.5) for the projection years 2030, 2050, and 2100.

According to the IPCC Fifth Assessment Report, the global mean sea level has risen more than 20 centimetres since 1880 and the trend is continuing at an unprecedented speed. Sea Level Rise is primarily caused by processes linked to global warming, such as the melting of glaciers and ice sheets, and the thermal expansion of water. Furthermore, the rising sea level leads to multiple negative effects like coastal erosion, inundations, storm floods, tidal waters encroachment into estuaries and river systems as well as contamination of freshwater reserves.

Sea Level Rise can affect coastal regions worldwide and regions will experience varying impacts based on their topography and mitigation measures. Munich Re provides hazard information on a 30m resolution for flooding hazard by sea-level rise globally. The extents of potentially flooded areas are given by storm surge events with a 100-year return period. Sea-level rise zones were modelled on the basis of high-resolution elevation data from the ALOS elevation model and sea-level rise projections from climate models. This enables the identification of five different hazard classes describing the potential hazard level by sea level rise, from no hazard to extreme hazard.

The sea level rise hazard information is available for the three RCP scenarios (RCP2.6, RCP4.5 and RCP8.5) and the projection year 2100.

Wildfires are a significant natural hazard, capable of being triggered both naturally and by human activities. They ravage vegetation and lead to the destruction of infrastructure and economic resources. Often, wildfires are followed by secondary effects such as erosion, landslides, impaired water quality, and smoke damage. The European Commission’s Joint Research Centre (JRC) highlights that climate change is altering meteorological conditions, impacting both the ignition and spread of wildfires. In response to this, Munich Re offers detailed information on wildfire conditions and an integrated Fire Weather Stress Index based on fire danger modeling.

Fire Weather Stress Index

The Fire Weather Stress Index is built upon the Fire Weather Index (FWI), a metric that encapsulates climatological conditions conducive to wildfires. The FWI, a numeric rating widely recognized in the field, amalgamates several factors: the probability of ignition, the speed and likelihood of fire spread, and the availability of fuel. This index is modeled using daily data on temperature, precipitation, humidity, and wind, primarily from the ERA5 ECMWF atmospheric reanalysis for the reference period. For future projections, the index incorporates data from the latest high-resolution local (CORDEX) and global (CMIP5) climate models.

The Fire Weather Stress Index synthesizes relevant information from the FWI time series, categorizing the fire weather stress situation on a scale from 0 (very low) to 10 (very high).

Key Parameters of the Fire Weather Stress Index

Available upon request in the Climate Expert Mode, the following key parameters describe climatological wildfire conditions:

The Fire Weather Stress Index, along with its underlying parameters, is available for both the reference period and for future scenarios under the RCP2.6, RCP4.5, and RCP8.5 scenarios for projection years 2030, 2050, and 2100.

Rising temperatures and alterations in precipitation patterns are leading to drier weather conditions, which in turn are causing more intense and frequent drought events. Such events have far-reaching economic, environmental, and social impacts. Recognizing this, Munich Re has developed an integrated Drought Stress Index to gauge the impact of climate change on current global drought conditions.

The Drought Stress Index is a nuanced tool that captures changes in the water balance, characterized by variations in precipitation and potential evapotranspiration. It is derived from the Standardized Precipitation-Evapotranspiration Index (SPEI), a state-of-the-art index for delineating drought conditions. The SPEI is a multi-scalar drought index grounded in climatic data, enabling the assessment of the duration, intensity, and severity of drought conditions against normal conditions during a reference period.

To compute the SPEI, daily information about temperature, precipitation, and humidity is utilized. This data is sourced from the latest high-resolution local (CORDEX) and global (CMIP5) climate models, providing a comprehensive view of drought conditions. These models are calibrated over a 35-year period up to 2005, focusing on the projection periods. The Drought Stress Index amalgamates information about projected drought durations and severities from the 9-month SPEI time series, with a range from 0 (indicating very low drought stress) to 10 (indicating very high drought stress).

Available for the three Representative Concentration Pathway (RCP) scenarios—RCP2.6, RCP4.5, and RCP8.5—and projection years 2030, 2050, and 2100, the Drought Stress Index is a vital tool for understanding future drought patterns. Furthermore, for the reference period, the meteorological drought parameter in the Climate Expert Mode is also accessible, based on ERA5 ECMWF atmospheric reanalysis data.

Global warming is significantly increasing the risk of heat stress, impacting humans, infrastructure, and ecosystems. With temperatures on the rise, both the intensity and frequency of heat waves are seeing an upward trend. In response to this growing concern, Munich Re offers detailed information on the meteorological threat posed by heat stress and an integrated Heat Stress Index.

Heat Stress Index

The Heat Stress Index is developed based on relevant heat parameters modeled from ERA5 ECMWF atmospheric reanalysis data (~25 km horizontal resolution) for the reference period. Additionally, it incorporates data from the latest high-resolution local (CORDEX) and global (CMIP5) climate models for future projections. This index amalgamates vital information from these parameters and categorizes the climatological heat stress situation on a scale from 0 (very low) to 10 (very high). The selection of parameters aligns with scientific studies and climate extremes indices as defined by the CCl/WCRP/JCOMM Expert Team on Climate Change Detection and Indices (ETCCDI), aiming to represent heat stress consistently on both local and global scales.

Key Parameters of the Heat Stress Index

Available upon request in the Climate Expert Mode, the following key parameters describe climatological heat conditions:

The Heat Stress Index, along with its underlying parameters, is available for the reference period and for future scenarios under the RCP2.6, RCP4.5, and RCP8.5 scenarios for projection years 2030, 2050, and 2100.

Due to global warming and in particular to warmer oceans, air contains more moisture. This can lead to an intensification of high-precipitation events and an alteration of the frequency of such events. The impact of climate change on precipitation is very heterogenous globally, which is caused by its fine-scale features. This makes it essential to use high-resolution climate models to capture the climate change impacts, which can lead to crop damage, soil erosion and increased flood risk.

Munich Re provides information on the threat by heavy precipitation in the form of detailed precipitation information as well as an integrated Precipitation Stress Index. Relevant precipitation parameters are modelled on the basis of ERA5 ECMWF atmospheric reanalysis data for the reference period and data from latest high-resolution local (CORDEX) and global (CMIP5) climate models for the future. The Precipitation Stress Index combines relevant information from the parameters characterising heavy precipitation and classifies the precipitation stress situation on a scale ranging from 0 (very low) to 10 (very high). The parameters were chosen in accordance to scientific studies and climate extremes indices defined by the CCl/WCRP/JCOMM ETCCDI, with the aim of depicting heavy-precipitation stress consistently, locally and globally.