An Experimental Study on The Correlation of Natural Rainfall Intensities and Raindrop Size Distribution Characteristics

Abstract

This paper aims to study the natural raindrop size distribution characteristics based on the experimental works for three (3) different rainfall intensities, which are 32.41 mm/h, 56.84 mm/h and 85.73 mm/h. A tipping bucket rain gauge was used to record rainfall data during the field study and a professional DSLR camera (Sony α6000) was used to the capture raindrop distribution during rainfall events. A sufficient number of photographs were taken with necessary adjustments on camera setting to produce the required sharpness of the images and to significantly reduce noise disturbances. Sharp images were selected for image segmentation using a customized coding script to further process the images on MATLAB. The segmented or processed images presented in the form of numerical data would provide the details on the number of drop counts in addition to the diameters of the individual drops captured. The raindrop sizes or diameters ranging from 0.5 mm to 4.5 mm were divided into group of 0.5 mm intervals. It is found that lower rainfall intensity at 32.41 mm/h has the highest volumetric drop distribution of 1.0–1.5 mm interval drop group 78.64%. The relatively higher rainfall intensity at 85.73 mm/h tends to produce higher counts in larger droplet sizes with increments of 6.90% for 2.5–3.0 mm and increment of for 3.45% 4.0–4.5 mm. The study also recorded a significant increment of median droplet sizes (D50) ranging from 1.18 mm to 1.33 mm as the rainfall intensity increased from 32.41 mm/h to 85.73 mm/h, respectively.