Major floods occurred during the 2011 monsoon season in Thailand. Provinces located in the Chao Phraya and Mekong River basin, including Bangkok and surrounding neighborhoods were most severely affected directly or indirectly by inundation. Flooding also affected most provinces in Thailand's south. Flooding began around July 2011, and continued into December 2011. Over 12.8 million people were affected, and the World Bank estimated damages reached 1,440 billion baht (US$45 billion) as of December, 2011. As of December 3, 2011 some areas still remained 6 feet underwater and many factory areas remained closed. The World Bank's estimate for this disaster means it ranks as the world's fourth costliest disaster as of 2011 surpassed only by the 2011 earthquake and tsunami in Japan, 1995 Kobe earthquake, Hurricane Katrina in 2005.
The flooding inundated about six million hectares of land, over 300,000 hectares of which is farmland, in 58 provinces, from Chiang Mai in the North to parts of the capital city of Bangkok near the mouth of the Chao Phraya. It has been described as "the worst flooding yet in terms of the amount of water and people affected". Seven major industrial estates were inundated by as much 3 meters (10 feet).