Evaluating Rainfall Intensity-Duration-Frequency Curves: A Comparison of Extreme Value Type I and Log-transformed Pearson Type III Distribution Methods in Bangladesh's Northern Region

In semiarid regions, the Intensity-Duration-Frequency (IDF) curves for rainfall are critical for managing water resources, as water scarcity is often the primary limiting factor. This study takes a comprehensive approach to generalize the relationship between daily rainfall and shorter-duration rainfall across varying return periods. Urban drainage infrastructures—like storm sewers, culverts, and other hydraulic designs—must be developed to address both drought and flooding issues. Daily rainfall data are typically sufficient for hydrologic and floodplain analyses related to designing and evaluating water control mechanisms, including polders, flood barriers, irrigation, and drainage systems. Small hydraulic systems such as culverts, storm drains, and drainage systems in urban areas or airports are often designed based on extreme rainfall data. This study utilized 44 years (1980–2023) of annual maximum rainfall data from the Bangladesh Meteorological Department (BMD). The Indian Meteorological Department's (IMD) empirical reduction formula was applied to estimate short-duration rainfall intensities using this data. IDF curves and equations were developed using the Log Transformed Pearson Type III (LPT III) and Extreme Value Extreme-Value Distribution methods. The results obtained using the Extreme Value method was slightly higher compared to the LPT III distribution results. The estimated rainfall intensities agreed with previous studies in certain areas of the study region. IDF equation parameters and correlation coefficients for various return periods (2, 5, 10, 25, 50, and 100 years) were determined using the least squares method. The results demonstrated high correlation coefficients, indicating the reliability of the equations in estimating IDF curves for the studied region. The study also found that rainfall intensity decreases as the duration increases, and those storms of any duration become more intense over extended return periods.