Heavy rain refers to intense, torrential rain that result in very high amounts of precipitation over a short period of time. Heavy precipitation events often occur in summer, typically associated with thunderstorms. One possible consequence is flash flooding, which can lead to flooding in areas far away from the location where the heavy rainfall event occurred. There is also a risk of flooding if, for example, the sewer system backs up. The ingress of water can damage buildings, vehicles and means of transport.
The K.A.R.L.® natural hazard model calculates the risk of heavy precipitation. The impacts of heavy rain are largely dependent the absorption capacity of the local sewage systems. In most cases, these wastewater systems are designed for a 3 to 10-year precipitation event (design rainfall). The decisive factor for risk assessment is how much this design rainfall volume is exceeded during a heavy precipitation event.
Hail
Hail is frozen precipitation with a diameter of at least 0.5 cm. Hailstorms can cause considerable damage to plants and animals, as well as to buildings, cars, aircraft, industrial facilities or people. Drainage systems on roofs or in streets can be blocked by hail, which can lead to water accumulation and thus to localized flooding.
The risk is determined using the hail model integrated into the K.A.R.L.® natural hazard model. The model is based on the calculation of a global hail potential, which incorporates various regional climate parameters (e.g., temperature, altitude of the zero-degree line, lightning frequency) that favor or prevent the occurrence of hail. For the hazard analysis, K.A.R.L.® first determines the local hail potential and then calculates the typical local return period for different hailstone diameters.
Snow/ice
During heavy snowfall, large amounts of snow accumulate in a short period of time. The weight of the snow masses not only damages trees, power lines and buildings, but also impairs the usability of transport infrastructure, which can lead to supply bottlenecks. In addition, large amounts of snow and ice often cause problems for agriculture and forestry as well as for the tourism and event industry.
The snow load values are determined based on globally available climate data. The modeling method for this purpose was calibrated using numerous specific local recommendations and building regulations from different climate zones and topographical altitudes around the world. Building-specific factors, such as the design, are not considered in the risk assessment. In addition, the analysis assumes that for the same amounts and durations of snow, regions where heavy snowfall occurs more frequently are less susceptible to damage.