The Diameter of Raindrops in Pontianak (West Kalimantan, Indonesia) in the Study of Variation and Its Relationship with Rainfall Intensity

Research has been carried out regarding the size of raindrop diameter in Pontianak city using a disdrometer. The purpose of this study was to determine the variation of raindrop diameter. The results show that for 2 years (2018–2019), the diameter of raindrops ranges from 4 to 12 mm, the minimum raindrops’ diameter 4.67 mm occurs in February, the maximum raindrops’ diameter 11.57 mm occurs in October, average raindrops diameter 7.85 mm, and median values raindrops diameter of 7.8 mm. When compared with the reference in 1976 at the same locations in a tropical climate, which states the average diameter of a raindrops is 3 mm and maximum raindrops diameter is 4.4 mm. This shows that there has been an increase in the size of raindrop diameter by 2–3 times from before. It is this change in the size of the raindrops that causes the potential for hydrometeorological disasters to get worse, both in quantity and in quality. This is because the larger the size of the raindrops, the higher the intensity of rain (floods, landslides, and moving ground) and the greater the speed of falling raindrops (landslide and moving ground). Raindrops measuring 12 mm will have a rain intensity of 322.36 mm/h and a falling speed hitting the ground of 24.2 m/s (equivalent to the momentum is 0.17 kg m/s) compared to raindrops measuring 5 mm, which only has a rain intensity of 134 mm/hour and a speed of falling raindrops of 10.08 m/s (equivalent to the momentum is 0.01 kg m/s).