Three people have been confirmed dead and another two are missing following a flash flood in the Keyi Panyor District of Arunachal Pradesh State, India, on Wednesday 24 June 2026. A further 54 families have been displaced by the incident, in which waters from the Rangandani River Dam Lake over-topped a wall surrounding a residential camp for employees of the North Eastern Electric Power Corporation working on the Panyor Lower Hydroelectric Project (also known as the Rangandani Dam), following days of heavy rain associated with the Summer Monsoon.
About thirty houses were destroyed at the dam workers colony, with another ten houses destroyed and fourteen damaged in related incidents in neighbouring communities, which have also been hit by flooding and landslide events caused by heavy rains in the area. Landslides are a common problem after severe weather, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall. Several major roads in the area have also been damaged, and the heavy rains are making air transport difficult, hampering the efforts of rescue workers.
Arunchal Pradesh has a monsoon season that begins around the end of April or beginning of May and ends around September, bringing 2-4000 mm of rain to the region each year. In the twenty four hours prior to the incident, 74 mm of rainfall had fallen in the area, which is high, but should not have been sufficient to cause flooding at a camp with flood defences on a dam lake where the water level can be controlled to some extent by releasing water from the dam. This has led to speculation that an earlier incident, such as a landslide, may have temporarily blocked the flow of the river upstream of the dam lake, and that when this temporary blockage failed, a large amount of water surged downstream overcoming the colony's flood defences.
Monsoons are tropical sea breezes triggered by heating of the land during the warmer part of the year (summer). Both the land and sea are warmed by the Sun, but the land has a lower ability to absorb heat, radiating it back so that the air above landmasses becomes significantly warmer than that over the sea, causing the air above the land to rise and drawing in water from over the sea; since this has also been warmed it carries a high evaporated water content, and brings with it heavy rainfall. In the tropical dry season the situation is reversed, as the air over the land cools more rapidly with the seasons, leading to warmer air over the sea, and thus breezes moving from the shore to the sea (where air is rising more rapidly) and a drying of the climate.
This situation is particularly intense in South Asia, due to the presence of the Himalayas. High mountain ranges tend to force winds hitting them upwards, which amplifies the South Asian Summer Monsoon, with higher winds leading to more upward air movement, thus drawing in further air from the sea. However, despite the incidents in Arunachal Pradesh this week, the Indian Monsoon is predicted to be be week this year, due to a developing el Niño system over the southern Pacific Ocean, leading to concerns that the country could suffer widespread droughts and famine this year.
The el Niño is the warm phase of a long-term climatic oscillation affecting the southern Pacific, which can influence the climate around the world. The onset of el Niño conditions is marked by a sharp rise in temperature and pressure over the southern Indian Ocean, which then moves eastward over the southern Pacific. This pulls rainfall with it, leading to higher rainfall over the Pacific and lower rainfall over South Asia. This reduced rainfall during the already hot and dry summer leads to soaring temperatures in southern Asia, followed by a rise in rainfall that often causes flooding in the Americas and sometimes Africa. Worryingly climatic predictions for the next century suggest that global warming could lead to more frequent and severe el Niño conditions, extreme weather conditions a common occurrence.
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