Impact of Deforestation on Recent Floods in Assam: Expert Insights

Understanding the Flood Triggers in Assam

Guwahati, July 31: The recent catastrophic floods affecting Jorhat, Sivasagar, and Charaideo districts have been primarily linked to the significant loss of forest cover in the upper regions of Nagaland. According to renowned river expert Professor Nayan Sharma, the intense rainfall led to an overwhelming flow of stormwater laden with silt, which inundated homes and elevated riverbeds.

Professor Sharma explained that a substantial flood hydrograph was produced by rapid, silt-heavy stormwater resulting from approximately 239 mm of rainfall recorded from July 18 to 20 in Mon district.

In an interview, the former IIT Roorkee professor noted that an estimated 800 square kilometers of forest have been lost in Nagaland from 2013 to 2023, a figure that may have increased. This reduction in stabilizing vegetation has intensified surface runoff and soil erosion, increasing by 1.5 to 2 times during heavy rainfall, adversely affecting watershed hydrology. Vegetation typically allows a significant portion of stormwater to seep into the groundwater, reducing surface runoff. Without this cover, stormwater and silt rushed into Assam, causing severe flooding and erosion.

He remarked that the force of the water was so great that residents struggled to evacuate or salvage their belongings. With silt now covering homes and agricultural land, the rehabilitation of affected individuals poses a significant challenge.

Professor Sharma highlighted the disconnect between macro and micro-level disaster management. While space-based assets like ISRO’s INSAT satellites can effectively monitor atmospheric changes, the data is not always translated into timely local alerts. Local disaster management units may still depend on manual processes rather than automated systems.

During the extreme rainfall events in Nagaland on July 18-19, water levels surged over 400% above normal. A critical issue identified was the absence of automated systems linking upstream hydrological sensors to the National Disaster Management Authority’s Common Alerting Protocol (CAP) platform.

He pointed out that deforestation and hill cutting in the Northeast exacerbate the problem, as rivers carry significant silt, leading to rising riverbed levels and reduced flood-carrying capacity. Observations of the Bhogdoi river revealed that in some areas, the riverbed was higher than the surrounding land.

Additionally, Professor Sharma noted that landslides in Arunachal Pradesh frequently lead to sudden floods in Dhemaji district. The Jorabat area, connecting upper and lower Assam, often experiences flooding after brief rain due to hill cutting in Meghalaya. He emphasized the need for regional cooperation to address these issues through a dedicated coordinating body.

For effective flood forecasting, satellite data products can be accessed for free from the Japan Space Agency’s JAXA site, which provides Global Satellite Mapping of Precipitation (GSMaP). Other satellites can also offer insights into atmospheric changes that may lead to extreme rainfall. Authorities should prioritize the implementation of AI-driven satellite-based flood forecasting systems to deliver timely alerts via geotargeted mobile notifications, potentially saving lives and property.

Professor Sharma further warned that as riverbed levels continue to rise due to silt accumulation, embankment breaches from overtopping are likely. Strengthening embankments in vulnerable areas with advanced surface armoring technologies, such as geocells and geogrids, is essential. Comprehensive watershed management, restoration of wetlands, and proper drainage systems must be prioritized, along with addressing encroachments in floodplains.

As a long-term strategy, the government should consider building medium-sized multipurpose dams with flood storage capabilities in the upper river reaches, such as Dikhow, Bhogdoi, and Desang, to mitigate the impact of extreme rainfall. Retrofitting existing hydel dams into multipurpose structures could also help manage floodwaters effectively, significantly reducing flood risks.