Evaluating 2021 extreme flash flood of Teesta River

Abstract Due to global warming, extreme hydroclimatic events (e.g., floods) are expected to happen more frequently and last longer. This study investigated such an extreme flood in the transboundary Teesta River that occurred in October 2021. We attempted to quantify the event's impact using data from time series flood levels, precipitation-related satellite images, and two-dimensional hydromorphological modeling. We found it challenging for people to cope with such a hazardous event since the depth of the flooding increased 6.98-fold in just 24 h. Our simulation results indicate that a sand-filled sediment measuring 0.27 m thick covered more than 33% cropland, and the velocity increased by almost 2.5 times. 136,000 individuals were marooned in the water. Compared to previous flooding events in its basin, which occurred in India and Bangladesh, the river appears to have some natural shock absorption features, i.e., a wide braided plain. We propose impact-based forecasting with a proactive early response as a valuable tool for managing such extreme events.