Friday 16 August 2019

Seventeen missing in landslide in Sichuan Province, China.

Seventeen people are still missing after a landslide hit construction workers working in a railroad in Ganluo County in in Siichaun slightly before 12.45 pm on Wednesday 14 August, The incident buried about 70 metres of the Lianghong-Aidai section of the Chengdu-Kunming Railway, while maintenance work was being carried out. Eleven people were pulled from the debris alive, but it is becoming increasingly unlikely that further survivors will be found as time passes. The landslide was the latest in a series of events in the area, triggered by exceptionally heavy rains across South China this summer. 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.

A section of the Chengdu-Kunming Railway, buried by a landslide on 14 August 2019. Liu Zhongjun/China Daily.

The climate of Sichuan Province is heavily influenced by the Asian Summer Monsoon, with heavy rainfall common in the summer. 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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