Why is Bangkok sinking?

Parts of Bangkok sank 10 cm a year. The reason is underground: soft clay, 10 to 15 metres thick. Below it, layers of sand hold groundwater. In the 1980s, wells pumped about 1.4 million cubic metres a day. Water drained out of the clay, and it squeezed down like a sponge. Around Hua Mak, the ground sank about 10 cm a year, from 1978 to 1985. Then pumping was curbed, and groundwater came with a bill. Nowadays, the ground sinks only about 1 cm a year. We tell you everything you need to know about Bangkok. Follow for more!

Bangkok stands on soft clay. When wells pumped out the groundwater below it, the clay squeezed like a sponge: around Hua Mak the ground sank about 10 cm a year in 1978–1985. Since pumping was curbed, Bangkok sinks about 1 cm a year on average.

• Bangkok's subsoil is mainly soft clay down to 10–15 m, over a sequence of sand and clay layers (JICA, 2006).
• In the 1980s, wells around Bangkok pumped an average of about 1.4 million m³ of groundwater a day; in 1954 it had been around 8,360 m³ a day (Soonthornrangsan et al., 2025).
• Pumping lowers the water pressure in the sand layers, so water flows out of the clay above and below them, and that flow compresses the clay (Bandara, 1997).
• Near Ramkhamhaeng University, at Hua Mak, the ground sank about 10 cm a year in 1978–1985 and about 1.3 cm a year in 2005 (Department of Groundwater Resources survey, reported by TCIJ).
• From 3 February 1985, groundwater bills were collected to limit pumping; the government's measures eventually slowed the sinking, which continues at around 1 cm a year on average (TCIJ; Soonthornrangsan et al., 2025).
• Satellite radar over Bang Kapi, the district that includes Hua Mak, measured yearly averages between about +2 and −5 mm in 2018–2022 (Pumpuang and Aobpaet, 2024).

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Sources:
– JICA and Nippon Koei (2006): The Study on Implementation of the BMA Subcenters Program in the Kingdom of Thailand (Case of Lat Krabang), Final Report, §5.3 Flood Protection Plan: https://openjicareport.jica.go.jp/pdf/11829579_07.pdf
– TCIJ (9 August 2015): Land subsidence caused by groundwater over-extraction in the Bangkok area at a rate of 2–3 cm/year and in certain areas up to 1 meter: https://www.tcijthai.com/news/2015/08/english/5725
– Bandara (1997): Relationship between subsurface geology and ground subsidence of Bangkok Metropolis, Thailand. Ceylon Journal of Science: Physical Sciences 4(1):47–59: https://dl.nsf.gov.lk/bitstreams/d3d5eebc-c3cf-47b6-9807-413717d3fa05/download
– Pumpuang and Aobpaet (2024): Evolution Pattern of Land Subsidence Using InSAR Time-Series Analysis in Bangkapi, Bangkok, Thailand. Journal of Current Science and Technology 14(3), Article 49: https://doi.org/10.59796/jcst.V14N3.2024.49
– Soonthornrangsan, Bakker and Vossepoel (2025): Linked Data-Driven, Physics-Based Modeling of Pumping-Induced Subsidence with Application to Bangkok, Thailand. Ground Water 63(2):145: https://pmc.ncbi.nlm.nih.gov/articles/PMC11875053/

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