What happened: Kerala’s flood impacts worsen when extreme rainfall hits modified river basins
Kerala’s intensifying floods are explained through a mechanism in which extreme rainfall interacts with river-basin conditions that have been modified by land-use change and changes to river channels and river management. The key proposition is that flood severity depends not only on rainfall intensity, but also on how rainfall becomes runoff and how rivers store and convey floodwater during heavy rainfall.
Background and earlier position: flood peaks depend on runoff, storage, and river conveyance
Flood outcomes in a river basin can be understood through a hydrology chain. Rainfall is converted into runoff in the catchment; some water is temporarily stored on the landscape through floodplains, wetlands, and vegetated areas; and the river channel then conveys the remaining flow downstream as a flood wave.
Natural flood buffers—such as functioning floodplains and wetlands—can slow down runoff and provide temporary storage. When these buffers are reduced, the landscape absorbs and delays less excess water, which can increase the likelihood of sharper and more damaging flood peaks.
What changed now: urbanisation and river-channel and management changes can amplify flood peaks
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