A survey of the effectiveness of flood maps on flood memory and risk perception: a case study from Kelani River Basin, Sri Lanka

Flood maps are important for the floodplain communities to identify the inundation regions and to make future decisions related to their behavior. The understanding of the flood maps may vary based on several factors, including age, education, previous flood experiences, income level and the length of the residence. Based on the memory/understanding of the flood maps, the risk perception of the communities can change and it may affect the reaction against the impending disasters. The memory of the risk information provided by the flood maps decays over time and it is important to know about this decays process to initiate awareness programs at suitable intervals to increase the risk perception.

To understand the effect of flood maps on the floodplain communities, a study was conducted in the Lower Kelani River Basin (LKRB), Sri Lanka. LKRB is susceptible to frequent flood conditions. Under the changing climatic conditions, the frequency and intensity of floods may further increase in future. To realize the study objectives, maps with return periods of 10-yr, 50-yr and 100-yr were distributed to a selected sample from LKRB and their understanding was assessed based on 2 interview surveys. First survey was conducted in April 2022 after the distribution of flood maps and the second survey was conducted in October 2022 with the participation of the same set of respondents. A total of 124 responses were used for the analysis. The understanding of the flood maps was evaluated based on a defined criterion. Furthermore, the risk perception of the community was assessed during the Survey 1 and 2.

As per the results of the surveys, a significant decline of the memory of the flood maps was observed from Survey 1 to 2. The level of education showed a significant correlation with the memory of the flood map contents. Further, a clear improvement of the risk perception was identified during the Survey 2. The community actions and engagement following the map distribution was crucial to translate the risk perception to actual behavior.