Abstract
Compound flooding, characterized by the co-occurrence of multiple
drivers is a cause of concern in many world river basins. High river
flows accompanied by high rain events are responsible for severe
flooding events. Many studies in the recent past have analysed rain and
river-flow dominated compound floods. In this study, we assessed the
rain and river-flow induced compound flooding scenarios in a large
tropical river basin, the Mahanadi River basin, located in eastern
India. Since, many high floods have occurred in the past decade in the
Mahanadi River basin, we analysed how the historical flood (in the year
2000) will unfold in a projected climate change scenario (in the year
2080) under RCP8.5. We used the bias-corrected hydro-meteorological data
of nine Global Climate Models (GCMs) as input forcings to a hydrologic
model MIKE11 NAM-HD to simulate the river flows at the head of the
Mahanadi delta. The mean areal rainfall for the delta region and the
river-flow simulations are forced into a calibrated and validated MIKE
FLOOD model to simulate the historical and projected flood inundations.
Comparison of the compound floods with the rain-induced and
streamflow-induced floods indicate increased compound flooding in the
projected scenario. Both historical and projected floods are found to be
predominantly influenced by the river flows. Also, both the areal extent
and flooding depth are found to be increasing the projected period as
compared to the historical counterpart.