Geological natural hazards such as earthquakes and volcanic eruptions are triggered by activities taking place in the earth's interior. Gravitational natural hazards are defined as landslides, rockfall, debris flows or avalanches, since rock, mud or snow masses slide down the slope due to gravity. They can be caused by earthquakes or by extreme weather conditions. Meteorological natural hazards are weather-related hazards such as heat, drought, forest fires, storms, floods, high water or heavy rain.
For risk and disaster management, chain reactions, domino effects and cascade effects in particular are a major challenge, since correlations or causes are not always (early) recognizable and when very complex precautionary measures have to be taken. An example of such chains of events was the earthquake off the Japanese coast on March 11, 2011. The tsunami triggered by this event caused severe damage to the nuclear power plant in Fukushima. This led to a nuclear accident.
Not all natural hazards can be detected or even predicted early on. Nevertheless, there are, for example, construction measures to protect against some of these natural hazards. However, concrete options for action can also be derived from these measures in order to quickly get to safety, to initiate evacuation measures or to act with foresight and planning. In this way, it is possible to avoid settling in flood areas, to build dikes, to install safety nets on slopes or to regularly check water levels. In addition, sensor technologies are now available that provide early information about an imminent danger or trigger an alarm if a measured value is exceeded, so that suitable protective measures can be initiated immediately. Inclinometers for slopes at risk of slipping or more complex early warning technologies such as those used for the early detection of tsunamis are worth mentioning here. There is a classic three-step procedure for the systematic recording of risks and the establishment of an associated risk management system, which is used to build up a corresponding precautionary system to cope with the crisis situation and to provide aftercare. This three-step procedure consists of the:
1. risk analysis: In this phase, possible dangers are identified and associated with possible damages that may result from the dangers. The question "What can or could happen?" is the main focus here. Often different scenarios (worst-case/best-case) are used here, which are oriented along the severity of an event.
2. risk assessment: Here the question "What may happen?" is central. This is where the risk situation and the assessment of possible dangers from the perspective of society are carried out. For example, what preventive measures does society expect, and what should be taken first in the event of damage? The answers to these questions form the basis for the third phase.
3. action planning: "Where can we start concretely, what needs to be done? These questions lead to the concrete action level. Based on the available financial, technical and human resources (e.g. existing know-how), it is now decided which measures are suitable and feasible to minimize existing risks for the population.
Economically strong industrial nations usually have better opportunities to develop costly adaptation strategies and precautionary measures for impending natural disasters at an early stage. For example, they can raise and reinforce dikes at an early stage if there is a medium or long-term threat of sea-level rise. These opportunities, which require high investments, are often not available to poorer societies. The focus there is often on improving living standards. But here, too, measures can be taken to significantly increase the chances of survival in the event of a disaster. This is more a matter of developing coping strategies. Here, too, these may include technical and structural protective measures, but also more extensive measures such as risk education, the creation of risk awareness, the preparation of risk and hazard maps, but also the marking of escape routes. All these are important precautionary measures to minimize the risk of natural hazards.