Developing a Flood Severity Index over India

Abstract:

The repetitive and destructive nature of floods in India causes significant economic damage, loss of human lives, and leaving the people living in flood-prone areas with fear and insecurity. To reduce the adverse impacts of these floods, the spatial distribution of its severity from the records of past events would greatly help in many aspects. However, the spatial distribution of the severity of the floods is not available over the country with the actual observational data. The unavailability of observational data of adequate fidelity has hindered observation-based studies in this area. In this study, a flood severity index map is derived over India. To accomplish this, we have created a unique event-based database for medium-range floods by collating information from various official sources and combining it with official flooding thresholds. The database includes coordinates of the gauge station, start time of the flooding event (when the flow exceeded the threshold), end time of the flooding event (when the flow dropped below the threshold), peak flow magnitude, peak flow time (when the peak flow occurred), time to peak (time taken to reach the peak from start time), recession time (time taken from peak time to end time) and the difference between start time and peak time. Taking advantage of this database, flood severity index over point gauges was derived. Further, various geomorphological, climatological, and meteorological variables were extracted to be used as explanatory variables for this index. Various statistical and machine learning models was trained and used to predict the index at ungauged locations. Finally, a flood severity index map is derived over India. With the developed flood severity index map, we were able to highlight the flash floods prone areas in gauged and ungauged regions in India based on official flood warning thresholds, which would be a great asset in various aspects of flood management and climatological evaluation of hydrologic model simulations. This can further be extended into flood risk and exposure models.