The district of Trincomalee is highly prone to flooding and has experienced frequent floods for the recent epochs, affecting over 0.32 million people when the flood occurred. The recurrent flood inundates the study area, particularly the coastal region that is densely populated and vulnerable to natural disasters. This flood is due to a combination of many factors, including increasing intensity of rainfall due to climate change, constructions buildings in low line areas or wetland reservations, poor maintenance of drainage canals in the city areas, and irrigation canals in the cultivation areas silting of tanks, increasing the volume of water from the Mahaweli Ganga and other rivers are the main caused for regular floods. Torrential rains inundate most of the low-lying areas damages agricultural and residential areas. This paper aims to analyse the vulnerable areas to flood and risk levels using a user-friendly application of open-source geospatial technology. This study was used to collect the exposure data using the community participatory method and the JOSM platform. OSM data and vulnerability areas were integrated into Digital Elevation Model. Elevation points were collected using Google Earth and TCX Converter. A vulnerability and flood risk area map was generated in combination with the factors such as elevation, floodwater depth, proximity to water bodies, rainfall intensity, and previous flood records. The rainfall analysis results show that the below-average rainfall with higher variability-CV28.8% in 1961-1990 and above-average rainfall had recoded from 1931-1960. As a result, the frequency of occurrence of floods was higher in the epoch mentioned above. SPI results revealed that out of 150 years of data, 40 years had experienced floods (P=0.266). The extreme flood were occurred in 1913, 1921, 1941, 1944, 1946, 1947, 1957, 1963, 1965, 1984 and 2011and severe floods were in 1896, 1898, 1898, 1923, 1935, 1949, 1961, 1971, 2015 and 2018. The flood risk assessment reveals, out of 230 GN divisions, about 30 GN are under the high hazard-prone areas, 52 GN under moderate risk, and 43 GN low-risk statuses.