With the increase of both magnitude and frequency of extreme hydrological events such as drought and flooding, the significance of adequately modeling extreme hydrological events is fully recognized. Estimation of extreme rainfall/flood for various return periods is of prime importance for hydrological design or risk assessment. However, due to the lack of knowledge and data limitation, uncertainty arising from extrapolating beyond available data is huge. In this book, different sources of uncertainty in statistical modeling of extreme hydrological events were studied in a systematic way. This was done by focusing on several key uncertainty sources using different rainfall duration and time distribution of rainfall with various return periods.