DEVELOPMENT OF IDF CURVE UNDER NON-STATIONARY METEOROLOGICAL CONDITION

In the present study, hourly data of rainfall for last 30 years (1983 to 2012) have been used to develop Intensity-Duration-Frequency (IDF) curve for Ahmedabad, Gujarat, India. To assess the effect of non-stationarity in rainfall record and development of IDF for study area, the data are sliced into three equal duration of 10 years, viz. 1983-1992, 1993-2002 and 2003-2012. Further, the IDF curves of each sliced duration are also prepared for different return periods. The derived IDF curves have indicated maximum rainfall intensity, for 5 minute duration and 2-year return period, as 88.83 mm/hr, 103.20 mm/hr and 115.23 mm/hr for 1983-1992, 1993-2002 and 2003-2012 respectively. It is observed that, for all three sliced IDF curve, the maximum intensity increases with time for various duration and frequency. The non-stationarity in the rainfall record is clearly observed as maximum rainfall intensity of a given duration has been found to be in increasing order from IDF curves derived for periods 1983-1992, 1993-2002 and 2003-2012. The analysis presented in the study concludes that non-stationarity in the meteorological data (rainfall) must be taken into account while deriving the IDF curves for designing of storm-water drainage system for urban areas.