Hydrological study links Upper Assam flash floods to extreme rainfall in Nagaland hill catchments
An official hydrological assessment says flash floods in Upper Assam were mainly triggered by extreme rainfall over Nagaland’s hill catchments, with runoff surm
An official hydrological assessment has found that the flash floods that inundated parts of Upper Assam last week were triggered primarily by extreme rainfall over Nagaland’s hill catchments. The report supports the Assam government’s position that the disaster did not begin only due to local rain in Assam.
Rainfall surge in Nagaland traced to steep catchments
The study analysed rainfall between July 18 and 20. It states that Nagaland recorded 85 mm of rain against a normal of 30.3 mm, which is an excess of 181%. It also highlights sharper spikes in several districts, including Mokokchung, Zunheboto and Kiphire.
According to the report, the heavy rain over steep hill terrain produced rapid runoff that fed river systems flowing into Assam. The assessment notes that this helped push rivers beyond their carrying capacity, leading to inundation in areas such as Sivasagar, Jorhat and Charaideo, along with damage to homes, agriculture, roads and other infrastructure.
Flooding also coincided with heavy rain in Upper Assam
The report does not rule out intense rainfall in Assam during the same period. It records exceptionally high rain amounts in several districts, including Charaideo, Golaghat, Jorhat and Sivasagar. However, it concludes that local rainfall alone cannot explain the scale of flooding seen downstream.
The assessment also describes how the same weather system triggered multiple landslides and flash floods across Nagaland, with particular mention of Mon district. This, it says, points to the strength of the event over upper catchments rather than a single local factor in Assam.
The findings align with Assam Chief Minister Himanta Biswa Sarma’s view that the situation needs deeper scientific study. He said the government would examine satellite imagery to understand what happened in Nagaland’s upper catchments and whether the event could repeat. The report-backed approach aims to help Assam strengthen long-term flood mitigation for downstream districts vulnerable to sudden river surges originating upstream.
