Severe flooding occurred during the 2011 monsoon season in Thailand. The flooding began at the end of July triggered by the landfall of Tropical Storm Nock-ten. These floods soon spread through the provinces of northern, northeastern, and central Thailand along the Mekong and Chao Phraya river basins. In October floodwaters reached the mouth of the Chao Phraya and inundated parts of the capital city of Bangkok. Flooding persisted in some areas until mid-January 2012, and resulted in a total of 815 deaths and 13.6 million people affected. Sixty-five of Thailand's 76 provinces were declared flood disaster zones, and over 20,000 square kilometres (7,700 sq mi) of farmland was damaged. The disaster was described by an unnamed Thai government official as "the worst flooding yet in terms of the amount of water and [number of] people affected".

Bangkok, officially known in Thai as Krung Thep Maha Nakhon and colloquially as Krung Thep, is the capital and most populous city of Thailand. The city occupies 1,568.7 square kilometres (605.7 sq mi) in the Chao Phraya River delta in central Thailand and has an estimated population of 9.0 million as of 2021, 13% of the country's population. Over 17.4 million people (25%) lived within the surrounding Bangkok Metropolitan Region at the 2021 estimate, making Bangkok an extreme primate city, dwarfing Thailand's other urban centres in both size and importance to the national economy.