# Frequency Analysis, Risk, and Uncertainty in Hydroclimatic Analysis

## Abstract

Analysis of extreme events like severe storms, floods, droughts is an essential component of hydrology and hydroclimatology. The extreme events have catastrophic impact on the entire agro-socioeconomic sector of a country as well as of the whole world. It has aggravated in a changing climate. Thus, it has become really important to predict their occurrences or their frequency of occurrences. This chapter focuses on different methods to analyze these extreme events and forecast their possible future occurrences. At the very beginning of the chapter, the concept of return period has been discussed elaborately which is the building block of any frequency analysis. However, identification of the best-fit probability distribution for a sample data is essential for any frequency analysis. Concept of probability paper is important in this regard, and its construction is discussed along with graphical concept of frequency factor. Next, the concept of frequency analysis is discussed using different parametric probability distributions, such as normal distribution, lognormal distribution, log-Pearson type III distribution, Gumbel’s distribution. Basic concepts of risk, reliability, vulnerability, resiliency, and uncertainty are also explained which are inevitable in any kind of hydrologic design based on frequency analysis of extreme events.