Thursday 16 July 2020

Landslide kills at least two in Sindhupalchok District, Nepal.

Two people have died and another three are missing following a landslide in the Sindhupalchok District of Nepal on Wednesday 15 July 2020. Landslides are a common problem in rural Nepal at this time of year, associated with the annual monsoon season. Landslides are a common problem after severe weather events, 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. All of the casualties are reported to be members of the same family, with the dead identified as Nimasyangbo Sherpa, 34, and Anji Sherpa, 16, while those missing are Somsang Sherpa, 84, Chhiring Sherpa, 12, and an as yet unidentified woman of 42. A further six households were forced to evacuate their homes following the incident, with another eighteen warned that they may need to evacuate if the area cannot be stabilised.

The site of the 15 July 2020 Sindhupalchok landslide. eAdarsha.

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.

Diagrammatic representation of wind and rainfall patterns in a tropical monsoon climate. Geosciences/University of Arizona.

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