Reconstituting past flood events: the contribution of citizen science

Abstract

Information gathered on past flood events is essential for understanding and assessing flood hazards. In this study, we present how citizen science can help to retrieve this information, particularly in areas with scarce or no authoritative measurements of past events. The case study is located in Yeumbeul North (YN), Senegal, where flood impacts represent a growing concern for the local community. This area lacks authoritative records on flood extent and water depth as well as information on the chain of causative factors. We developed a framework using two techniques to retrieve information on past flood events by involving two groups of citizens who were present during the floods. The first technique targeted the part of the citizens' memory that records information on events, recalled through narratives, whereas the second technique focused on scaling past flood event intensities using different parts of the witnesses' bodies. These techniques were used for three events that occurred in 2005, 2009 and 2012. They proved complementary by providing quantitative information on flood extents and water depths and by revealing factors that may have contributed to all three flood events.

A method to reconstruct flood scenarios using field interviews and hydrodynamic modelling: application to the 2017 Suleja and Tafa, Nigeria flood

“…In the study, flood depths and extents were retrieved for multiple flood events (between 2005, 2009, 2012) based on personal recollections using two (independent) sets of community representatives. Sy et al (2020) observed a good agreement after comparing flood spatial extents derived with a communitybased approach and remotely sensed data. Given observed progress in the application of community-based data and the urgent need for understanding flood risk, especially in vulnerable regions, Assumpção et al (2018) and Sy et al (2020) have recommended exploring new alternatives in integrating such data into hydrodynamic models in data-scarce regions.…”

“…Recent reviews by Assumpção et al (2018) and Sy et al (2019) showed that studies that utilize data, collected from affected communities, to reconstruct past flood scenario are increasing. Such an approach, using knowledge from affected communities, is particularly encouraged in data-scarce regions given their potential to provide low cost and sizeable data with good spatial and temporal coverage (Sy et al 2019(Sy et al , 2020Assumpção et al 2018). For example, several studies have reconstructed past floods using either water depths and velocity retrieved from texts, pictures and videos uploaded to social media platforms (see review by Assumpção et al 2018)) or flood duration derived using interviews (e.g.…”

“…Focussing on field visits, several researchers have integrated face-to-face interviews for the collection of post-event observations and subsequent application for past flood reconstruction using a GIS approach (e.g. Poser and Dransch 2010;Singh 2014;Sy et al 2016Sy et al , 2020. A recent advancement in mapping past floods in typical data-scarce regions using interviews was carried out by Sy et al (2020) in Yeumbeul North, Senegal.…”

“…Poser and Dransch 2010;Singh 2014;Sy et al 2016Sy et al , 2020. A recent advancement in mapping past floods in typical data-scarce regions using interviews was carried out by Sy et al (2020) in Yeumbeul North, Senegal. In the study, flood depths and extents were retrieved for multiple flood events (between 2005, 2009, 2012) based on personal recollections using two (independent) sets of community representatives.…”

A generic physical vulnerability model for floods: review and concept for data-scarce regions

“…Furthermore, vulnerability indices have been identified to lack a stand-alone meaning outside a relative comparison of building vulnerability (Tarbotton et al, 2012;Dall'Osso and Dominey-Howes, 2013). This is a major limitation given the quality of information contained in the vulnerability index.…”