Rain Drop Size Distribution Modelling in Singapore - Critical Diameters

This paper analyzes and presents the measured drop size distribution (DSD) for five rain rates 4.20, 22.80, 66.54, 100.57 and 141.27 mm/hr in Singapore (1deg20'N, 103deg41'E). The ranges of rain drop diameters that are critical to the DSD are identified and the significance of their relationship is analyzed. The modified gamma model is used to describe the DSD in Singapore. Root mean square error (RMSE) in percentage is calculated for all the rain rates for both lognormal (using maximum likelihood estimators and using moment estimators) and modified gamma models. Over the critical diameter range (0.771 mm to 5.3 mm), the modified gamma model fits very well with the measured data and produces least RMSE compared with other models except at the lower rain rate considered.