Guwahati: Just two days of intense rainfall in Nagaland have kept parts of Upper Assam flooded for five days, underscoring how short, extreme rain spells can outweigh an overall monsoon deficit and cause widespread devastation if downstream communities are not warned in time.Despite below-normal seasonal rainfall across the northeast, Nagaland received nearly 100% excess rain over the past week. Heavy to very heavy rainfall in Mon, Mokokchung and Longleng districts on Sunday and Monday triggered landslides and flash floods in Nagaland and sent a surge of water into the adjoining Assam districts of Sivasagar, Charaideo and Jorhat. The Assam govt has attributed the flooding primarily to very heavy rainfall in neighbouring Nagaland between July 18 and 20.The Dikhou and Disang rivers in Sivasagar remained above the danger level on Thursday evening, according to the Central Water Commission. The Dikhou was still rising. The CWC places the danger levels of the Dikhou at Sivasagar and the Disang at Nanglamoraghat at 92.40 metres and 94.46 metres, respectively.IMD data show that the rainfall was heavily concentrated over two days. Longleng recorded 79.8 mm on Sunday and 52.7 mm on Monday before rainfall declined to 19.7 mm on Tuesday and 3.8 mm on Wednesday.Mokokchung received 85.4 mm and 69.2 mm on Sunday and Monday, followed by 12.6 mm on Tuesday and 2.2 mm on Wednesday.In Mon, rainfall rose from 44 mm on Sunday to 137 mm on Monday. The observatory recorded no rain on Tuesday and 14 mm on Wednesday. Mon was among the worst-hit districts, while flash floods and landslides also caused extensive damage in Mokokchung and other parts of Nagaland. (ipr.nagaland.gov.in)Although the rainfall did not fall in the IMD’s “extremely heavy” category, it triggered massive landslides in Nagaland and severe flooding downstream in Assam.The Assam State Disaster Management Authority attributed the floods mainly to rainfall, but experts said detailed data analysis and field studies would be required to establish whether changes in drainage and land use intensified the disaster.State parliamentary affairs minister Pijush Hazarika told the assembly on Wednesday that the devastating upper Assam floods were caused by an extraordinary natural calamity triggered by massive water inflows from Nagaland’s hills.“A detailed assessment is needed to determine whether natural drainage channels have been obstructed or their water-carrying capacity has declined. Factors such as deforestation and hill cutting in the upstream areas may also have contributed to landslides,” said Prof Dhrubajyoti Sahariah of the geography department at Gauhati University.The flooding has also highlighted the need for faster sharing of rainfall and river-flow information between upstream and downstream administrations, particularly during short spells of intense rain.All seven northeastern states have recorded deficient rainfall since June 1. Up to Wednesday, Nagaland was 6% below normal and Assam 24% deficient, while Manipur had the region’s highest deficit at 46%.Between June 1 and July 22, Nagaland received 460.7 mm of rainfall and Assam 557.6 mm, showing how seasonal averages can mask the threat posed by intense, localised downpour.
