Impacts of floods on Colombo during two decades: Looking back and thinking forward

This research contributes to the current debate on linking flood events and developmental pressure in urban areas. Colombo District has faced frequent flood events during the last two decades which disrupted the socio-economic and environmental setup. Colombo district is the economic hub and the administrative capital of Sri Lanka and it is the area with highest population density in the country. It has experienced rapid urbanization and Land Use Land Cover Changes (LULC) during recent past. The new infrastructure project developments, expansion of impervious spaces, disturbances to the drainage systems have increased the occurrence of floods. This study was carried out to identify areas with the highest flood damage and attempted to find out any the link between population and land use changes with flood impacts from 1999 to 2018. We used Satellite images, Remote Sensing Techniques and Weighted Overlay method in Geographical Information System to detect the LULC change and the flood vulnerability together with population and disaster related data. The results show that north and western parts of Colombo district were mostly affected by floods. The areas with high flood vulnerability have increased by 1.29% while moderately vulnerable areas have increased by 3.76%, and low vulnerable areas have decreased by 5.04%. The total settlements in Colombo district have increased by 20.08% and have had significant increase by 29.60% in the areas with high flood impacts. The results of the present study highlight the threat of unsustainable urban expansion on floods and call for prompt management action for resilience.