Just weeks after the 4-month-long monsoon season commenced in June, “thousands of people are out of their homes, [and] fields and wildlife sanctuaries are under water in Assam,” said hydrologist Dulal Goswami. Goswami is a professor retired from Guahati University in Assam, a state in northeastern India that is ravaged by floods from the Brahmaputra River every year.
India accounts for one fifth of global flood deaths; an average of 1,650 Indians lost their lives every year between 1953 and 2016 as a result of floods. About 40 million hectares in India are prone to flooding, and economic losses average close to US$7 billion each year.
Flood management in India is very complex, according to a new review by researchers at the Indian Institute of Technology (IIT) Bombay. Factors influencing flood management include variables associated with climate change: sea level rise, the intensity and frequency of flood events, and the predictability of downpours. Policy makers must also evaluate the social and economic dynamics of India’s population. Urban floods are a particularly evolving risk due to unplanned city growth and poor drainage infrastructure, the report says.
“The extensive review agglomerates relevant statistics and data patterns on flood management in India, which otherwise is difficult to be analyzed by looking at any individual study,” said lead author Mohit Mohanty.
India’s current flood management strategy largely focuses on structural measures such as embankments and dykes. A mixed approach that includes nonstructural measures such as flood forecasting and community participation in flood risk management would help, researchers concluded.
Four Zones, Multiple Approaches
The IIT team divided India’s flood-prone areas into four river regions: the Brahmaputra, the northwest, the Ganges, and central India and Deccan. Each region has its own flood patterns, and the team recommended flood management approaches tailored to fit each.
In the Brahmaputra region in India’s northeast, for instance, incessant rainfall can be aggravated by earthquakes and landslides, disrupting the natural flow of the river. In addition to structural enhancements such as reinforced embankments, the authors said this region would benefit from greater coordination between India’s Central Water Commission (CWC) and local authorities. Although the CWC releases consistent flood forecasts, the “local administration is not able to use it properly due to a lack of skilled personnel,” the review says.
Causes of floods in the northwest river region vary across the area’s diverse landscapes and require flood mitigation strategies more dependent on infrastructure such as dams and levees. In the Himalayas, flooding is most associated with cloudbursts and glacial lake outbursts. In the arid regions of Rajasthan, thin soil sits atop impermeable layers of bedrock and hard calcium, which prevent water infiltration. In the agriculture-dominated “food bowl” of Punjab, flooding may be more associated with inadequate drainage facilities in irrigated fields.
In the Ganges region, the impact of heavy rainfalls is augmented by earthquakes and unregulated sand mining, which destabilizes riverbeds. Moreover, the Ganges is the most populous river region in the world, and the “high density of population [and] radical land use changes combined with pervasive poverty render flood management a unique global challenge,” said the authors. To address the increasing prevalence of urban flooding along the Ganges and elsewhere in India, researchers recommended improved drainage systems, a real-time flood forecasting system, strict implementation of building codes, and demarcation of flood zones.
The central India and Deccan region is prone to sea level rise, severe coastal erosion, and tidal flooding caused by cyclones. Dams in the region, the authors said, “still follow the conventional ‘Rule Book’ rather than computer-based modeling.” In addition to modernizing dam oversight, they said, watershed vegetation could help prevent soil erosion and sediment deposition.
Overall, the flood-carrying capacity of India’s huge river network is rapidly decreasing because of bank erosion and a rise in sedimentation in the streambed. Both phenomena trigger breaches of flood dykes, said Nayan Sharma, an adjunct professor of water resources at IIT Roorkee who was not involved in the study. Compounding the problem are rapidly shrinking wetlands in India’s floodplains, which would have absorbed water, he added.
Sharma also pointed out that flood detention measures are absent “in most of the 5,500 dams in India,” concepts of embankment construction are “outmoded,” and the country lacks the latest forecasting systems.
The Way Forward
The IIT Bombay researchers recommended that India’s flood management policy should shift from a “passive response” that relies mainly on structural measures to a “progressive response” that emphasizes nonstructural measures such as forecasting, land use planning, warning outreach, and floodplain mapping.
Researchers also recommended a greater role for community leadership in management policy, especially in the Brahmaputra and Ganges regions. Goswami, too, emphasizes the need to shift from engineering restrictions to a “holistic, sustainable, and people-friendly” river management system.
—T. V. Padma (@tvpadma), Science Writer