Climate change and dam management intensify flood risks in India

By Raj Kumar Sinha*
Due to the average global temperature increase, there has been an increase in prolonged periods without rain and sudden, extreme rainfall events leading to floods. Just before the disaster, Wayanad, Kerala, experienced unprecedented rainfall. The district received 6 percent of its annual average rainfall in just one day. Over the past few years, climate change has been affecting the intensity and frequency of rainfall. Heavy rainfall in a short period suddenly increases the risk of flooding.
Heavy rainfall does not necessarily mean that the total amount of rainfall in a location has increased. It means that rainfall is occurring in intense events. Changes in rainfall intensity, when coupled with changes in the interval between rainfall events, can lead to changes in total rainfall. It is important to monitor the frequency of heavy rainfall events and calculate what percentage of a particular location's total rainfall in a given year has come in the form of extreme one-day events.
India is highly susceptible to widespread flooding because the country receives more than 70 percent of its annual rainfall during the four-month period from June to September. Excessive rainfall does not cause flooding in most river basins because its nature is fragmented. The transformation of excessive rainfall into floods depends on the catchment area. Therefore, it is essential to focus on flood monitoring and forecasting efforts, keeping in mind the spatial extent of excessive rainfall and the catchment area. If this is not heeded, controlling and managing the increasing flood events due to a warming climate could become challenging.
Another important aspect is to assess siltation in dams. This will allow for water planning according to the current water storage capacity in the reservoir. The structure of the Bargi reservoir is such that the speed of the sediment particles flowing from its upper reaches does not decrease. Instead of settling in the outer parts, most of the sediment flows rapidly into the main reservoir and settles at the bottom. There is a need to deeply understand the erosive and sediment size changes in the Bargi dam.
This information illustrates the complex relationships between dams, stream-bed erosion, sediment, and flood risk. The uncertainty of flood assessment over the thousands of square kilometers of catchment areas of large reservoirs, compared to small reservoirs, increases flood risk. Continuous rainfall in the dam's catchment area increases the water flow, making it necessary to open the dam's gates, leaving no way to prevent flood disasters downstream. Consequently, the districts along the Narmada River below the Bargi dam, such as Jabalpur, Narsinghpur, and Narmadapuram, have suffered significant economic losses in recent days, and all transportation routes were blocked. Thus, instead of controlling floods, the dam increases their intensity.
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*Senior activist of the Bargi Dam Displaced Persons Association