A Multidimensional View of Flood Regimes in the Narmada Basin, India

Flood hazards in large river basins are shaped by multiple interacting factors, including how long a flood lasts, how high the peak flow becomes, and how much water passes through the river system. Traditional approaches that focus only on the flood peak often miss important aspects of flood behaviour and can underestimate risks, especially for long, slowly building floods or short, intense flash events. This study provides a basin-wide assessment of flood characteristics in the Narmada River Basin, India, using 50 years of daily streamflow data from 13 monitoring stations. Instead of analysing peak flows alone, we consider three dimensions of flood behaviour—peak discharge, volume, and duration—and combine them into two complementary metrics. The Short-Duration Flood Index (SDFI) highlights quick, intense floods typically driven by burst rainfall and rapid runoff, while the Long-Duration Flood Index (LDFI) represents slower, persistent floods that build up over days as catchments saturate. These indices allow floods to be compared across the entire basin despite large differences in catchment size and hydrologic setting. The analysis reveals clear spatial contrasts in flood behaviour. Upstream mountainous and plateau regions experience more sustained, long-duration floods, reflecting greater storage and slower runoff processes. Mid-basin tributaries show pronounced flashiness and frequent short-duration floods driven by intense rainfall and limited buffering capacity. Downstream areas receive the highest overall flows as water converges from upstream, but exhibit mixed characteristics depending on event type and rainfall distribution. Importantly, the index-based approach identifies severe flood events that traditional peak-only assessments tend to overlook. By capturing both flash floods and slow-building high-volume floods within a single framework, the method provides a more complete picture of basin-wide flood hazard. Although demonstrated in the Narmada Basin, the approach is applicable to other major river systems and can support flood mitigation planning, early-warning design, and water-resource management—especially as climate change continues to alter rainfall patterns and flood regimes.

Keywords: Multivariate flood analysis; Flood indices; Flood frequency analysis; Hydrological extremes; Narmada River Basin