Paluuaika

Paluuaika is a statistical concept used especially in hydrology, meteorology and risk assessment to describe the recurrence interval or return time of a specified extreme event. It expresses, on average, how often an event of a given magnitude or larger is expected to occur under a chosen statistical model.

Calculation relies on a probabilistic framework. In a simple Poisson model with rate lambda of events per year, the paluuaika T is 1/lambda. When expressed as annual exceedance probability p, the return period is approximately 1/p. For example, a 100-year flood has a 1% chance of being exceeded in any given year, and thus a paluuaika near 100 years.

Important caveats include that paluuaika is an average over many realizations, not a guaranteed schedule. Real-world events can cluster; data are finite; and non-stationarity—such as climate change—can alter event frequencies, making historical paluuaika estimates less reliable for future planning. The concept also depends on the chosen threshold or magnitude and the assumed statistical model.

Applications include civil engineering, flood risk assessment, dam and bridge design, insurance, and land-use planning. Paluuaika informs design standards and risk communication but must be interpreted with awareness of model assumptions and uncertainties.

See also: Recurrence interval; Return period; Extreme value theory; Exceedance probability.