Frequency Analysis

Why the Frequency Analysis is important?

Hydrologic systems can be affected by extreme events such as heavy storms, floods, and droughts. These events vary in severity, and generally, the more severe an event is, the less often it occurs. This relationship—between how extreme an event is and how frequently it happens—is the focus of frequency analysis in hydrology.

The goal of frequency analysis is to use probability distributions to estimate how often extreme events of a certain magnitude are likely to occur. This requires reliable hydrologic data, which should be independent and identically distributed. To meet this requirement, analysts often use the annual maximum value of a variable (e.g., the highest river flow in a year), assuming these yearly values are independent from each other.

It is also assumed that the hydrologic system is random (stochastic), and not affected by time or space—meaning that events are not influenced by trends or specific locations.

The results of this analysis are important for a wide range of engineering and planning applications. They help in designing infrastructure such as dams, bridges, culverts, and flood control systems. They are also used to assess the economic benefits of flood protection projects and to map floodplains and evaluate how land use changes may affect flood risks.