;Abstract Raindrop size distribution (RSD) has significant implications meteorology, hydrology, remote-sensing, radio-wave communication and in hydrology. In this thesis an attempt has been made to comprehend RSD characteristics of seasonal, and tropical cyclones rainfall at different observational sites located in Indo-Pacific region as well as to assess the rainfall erosivity for Taiwan region that was induced due to tropical cyclones (also called typhoons). To achieve the above mentioned goals, a wide range of ground-based (disdrometers, radars and rain gauges), remote-sensing (MODIS and TRMM), and re-analysis (ERA-interim) data sets have been used. A comparison study conducted for the summer season (16 June -31 August) RSD characteristics for Palau and Taiwan observational sites showed clear demarcations in RSD between these two islands. Rainfall over Taiwan has a higher concentration of mid and large drops than Palau. The rain integral parameters as well as other gamma parameters showed clear distinction between these two islands. Both complex topography (central mountain range) and relatively higher aerosol loading were found to be the causative mechanism responsible for these RSD variation between these two islands. The RSD characteristics of summer (16 June -31 August) and winter (December-February) seasons rainfall over north Taiwan reveled a higher concentration of large drops in summer and small drops in winter. Both remote-sensing and re-analysis data sets revealed that the deeply extended clouds with intense convective activity and relatively higher ground temperatures in summer are responsible for the RSD distinctions between summer and winter seasons. The statistical analysis of RSD characteristics for Indian and Pacific Ocean tropical cyclones (TCs) revealed that the number concentration of small drops is higher in TCs of Indian Ocean than Pacific Ocean, whereas, the number concentration of mid-size and large drops is higher in Pacific Ocean TCs. The radar reflectivity- rain rate (Z-R) and slope- shape (μ-Λ) relations of Indian Ocean and Pacific Ocean are found to be distinctly different. The rainfall erosion caused by typhoon rainfall over Taiwan are assessed by using fifteen years of RSD and 60-years of hourly rain gauges data, and established that typhoons’ mean rainfall erosivity is higher than the global mean rainfall erosivity. Moreover, regional variability of typhoons rainfall erosivity showed an increasing pattern from north to south, with relatively higher values over eastern and southern part of Taiwan.
