Why Assam is Witnessing Unprecedented Flooding

Context

Assam has been experiencing one of its most severe flood events in recent years, resulting in significant loss of life and large-scale displacement. Floodwaters peaked on 19 July, affecting more than 7 lakh people, while over 1.15 lakh people sought shelter in relief camps.

Key Highlights

• As floodwaters gradually receded, nearly 6.54 lakh people across 810 villages in 10 districts remained affected, according to the Assam State Disaster Management Authority (ASDMA). Some areas of Sivasagar district continued to remain inaccessible.
• The State initially linked the flooding to a cloudburst in Mon district of Nagaland. However, the Meteorological Centre, Kohima, clarified that the rainfall did not qualify as a cloudburst, as 137 mm of rain fell over 8–9 hours, rather than exceeding 100 mm within one hour.
• The Chief Minister stated that rainfall recorded over 18,19 July in parts of Nagaland and Assam’s Charaideo district was unprecedented, surpassing a similar rainfall event recorded in 2017.
• Experts attribute the floods to multiple factors, including reduced groundwater infiltration in urban areas, riverbank excavation and mining, which increase sediment deposition and reduce river carrying capacity, and deforestation in upstream watersheds. They have also emphasised the need for extensive afforestation and improved rainfall forecasting systems.

Key Concepts

Cloudburst

• According to the India Meteorological Department (IMD), a cloudburst is rainfall exceeding 100 mm in one hour over a limited geographical area.
• Such events are generally associated with rapid uplift of moisture-laden air over mountainous terrain.

Brahmaputra River System

• The river originates as the Yarlung Tsangpo in Tibet near Mansarovar.
• It enters India through Arunachal Pradesh as the Siang (Dihang), becomes the Brahmaputra in Assam after joining the Dibang and Lohit rivers, and enters Bangladesh as the Jamuna.
• It is a braided, sediment-rich river, making it highly vulnerable to channel migration, erosion and flooding.

Why Assam is Highly Flood-Prone

• Assam accounts for nearly 10% of India’s flood-prone area.
• Major causes include intense monsoon rainfall, steep Himalayan catchments feeding into a low-lying floodplain, heavy sediment deposition, seismic activity (including changes caused by the 1950 Assam earthquake), and occasional embankment failures.

Assam State Disaster Management Authority (ASDMA)

• Constituted under the Disaster Management Act, 2005, ASDMA is the State’s apex disaster management body.
• It is chaired by the Chief Minister and is responsible for disaster preparedness, mitigation and response.

Disaster Management Act, 2005

• The Act established India’s three-tier disaster management framework comprising the National Disaster Management Authority (NDMA), State Disaster Management Authorities (SDMAs) and District Disaster Management Authorities (DDMAs).
• It also provides for institutions such as the National Disaster Response Force (NDRF), National Institute of Disaster Management (NIDM) and disaster response funds.

Percolation and Surface Runoff

• Percolation refers to the downward movement of water into soil and aquifers.
• When land becomes compacted, paved or deforested, infiltration decreases while surface runoff increases, intensifying flood peaks and sediment transport.

Extreme Rainfall Events

• IMD observations indicate a rising frequency of very heavy (>115.5 mm/day) and extremely heavy (>204.5 mm/day) rainfall events.
• A warmer atmosphere can hold nearly 7% more moisture for every 1°C increase in temperature, contributing to more intense rainfall episodes.

Causes :

1. River bank erosion problem
2. ⁠Climate change
3. ⁠Deforestation/ Rapid loss of Forest Cover
4. ⁠Excessive Excavations of River Valley sides (likely because of Mining)
5. ⁠Overflow of Bhramaputra and its tributaries
6. Inadequate watershed management & Flood forecasting 

Way Forward

• Shift from an embankment-focused strategy towards integrated river basin management, including floodplain zoning, wetland restoration and catchment afforestation.
• Improve impact-based flood forecasting through satellite-based precipitation monitoring, hydrological modelling and enhanced upstream data sharing among Nagaland, Arunachal Pradesh and Assam.
• Regulate riverbed mining and hill-slope excavation to reduce sediment accumulation and preserve river channel capacity.
• Establish a North-East river basin authority to strengthen coordinated inter-state and transboundary data sharing and flood management across the Brahmaputra basin.