100årsflöden

100årsflöden, or 100-year floods, are a concept used in hydrology and flood risk management to describe a flood event that has a 1% probability of occurring in any given year. This does not mean that such a flood will only happen once every 100 years, but rather that the probability of a flood of that magnitude occurring in any year is one in one hundred. These events are statistically derived based on historical rainfall and river flow data.

The term "100-year flood" is often misunderstood. It is a statistical measure of probability, not a prediction of frequency. Therefore, it is possible for multiple 100-year floods to occur within a short period, or for a period of 100 years or more to pass without such an event occurring. The actual magnitude of a 100-year flood can vary significantly depending on the specific river basin, its geography, climate, and other factors.

Understanding 100-year flood levels is crucial for urban planning, infrastructure development, and the implementation of flood defense measures. Building codes and land-use regulations in many areas are often based on these flood levels to mitigate potential damage and loss of life. Hydrologists use complex models and historical data to estimate these flow rates, which are then used by authorities to inform decisions about development in flood-prone areas.