Short-duration rainfall analysis for Bangladesh

Various methods exist for developing Intensity-Duration-Frequency (IDF) curves, each potentially leading to significantly different engineering decisions. To develop IDF curves for short-duration rainfall, observed pluviograph data is needed, which, however, is limited for Bangladesh. In this case, empirical methods are adopted to estimate short-duration design rainfall values where 24 h design rainfall is reduced to a short duration using a factor. This study compares two widely used approaches for Bangladesh: the empirical intensity reduction formula proposed by the Indian Meteorological Department (IMD) and the rainfall depth ratios recommended by the World Meteorological Organization (WMO). Hourly rainfall values were initially derived by frequency analysis, followed by power regression to develop smoothed IDF curves for durations ranging from 5 min to 12 h. The analysis showed that WMO estimates were consistently higher than IMD by about 3 to 5% for durations below 24 h, with differences slightly increasing at longer sub-daily durations. The IMD-derived curves were generally closer when benchmarked against Brisbane, Australia. The WMO approach produced systematically higher values by about 4 to 7% across all the selected stations. This study is being continued to develop a design rainfall portal and guideline for Bangladesh like Australia.