Abstract
During and just after flash flood, data regarding water extent and inundation will not be available as the traditional data collection methods fail during disasters. Rapid water extent map is vital for disaster responders to identify the areas of immediate need. Real time data available in social networking sites like Twitter and Facebook is a valuable source of information for response and recovery, if handled in an efficient way. This study proposes a method for mining social media content for generating water inundation mapping at the time of flood. The case of 2015 Chennai flood was considered as the disaster event and 95 water height points with geographical coordinates were derived from social media content posted during the flood. 72 points were within Chennai and based on these points water extent map was generated for the Chennai city by interpolation. The water depth map generated from social media information was validated using the field data. The root mean square error between the actual water height data and extracted social media data was ± 0.3 m. The challenge in using social media data is to filter the messages that have water depth related information from the ample amount of messages posted in social media during disasters. Keyword based query was developed and framed in MySQL to filter messages that have location and water height mentions. The query was validated with tweets collected during the floods that hit Mumbai city in July 2019. The validation results confirm that the query reduces the volume of tweets for manual evaluation and in future will aid in mapping the water extent in near real time at the time of floods.
Highlights
Change in climate, urbanization and other human activities across the globe disturbs the hydrological cycle and cause various water related issues like water pollution, floods, droughts, etc., (Lyu et al 2019a; Luo et al 2019, 2020)
During Chennai flood 2015, authorized official report on inundation map was released by Disaster Management Support (DMS) Division, National Remote Sensing Centre (NRSC/Indian Space Research Organization (ISRO)), India on March 2016 after a field survey that was carried out on December 24 to 26, whereas flood disaster occurred on December 2 2015 (National Remote Sensing Centre 2015)
The Facebook pages related to Chennai flood, 2015 and the Twitter search query was given in Additional file 1
Summary
Urbanization and other human activities across the globe disturbs the hydrological cycle and cause various water related issues like water pollution, floods, droughts, etc., (Lyu et al 2019a; Luo et al 2019, 2020). In general inundation map is prepared based on the field data, remote sensing data and hydraulic models(Grimaldi et al 2016). Utilizing remote sensing data for rapid water extent mapping have some limitations that includes restricted availability(Mason et al 2012), limited spatial and temporal resolutions(McDougall and Temple-Watts 2012). Apart from these traditional data content, user generated crowd sourced content called volunteered geographical information(VGI) were widely used for water extent mapping and validation(McDougall 2011; Hirata et al 2018; Rollason et al 2018). As the data from social media are posted real time with no time delay, the same can be mined for rapid water inundation mapping
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