On 16 August 2018, severe floods affected the south Indian state Kerala, due to unusually high rainfall during the monsoon season. It was the worst flood in Kerala in nearly a century. Over 483 people died, and 15 went missing. About a million people were evacuated, mainly from Chengannur, Pandanad, Edanad, Aranmula, Kozhencherry, Ayiroor, Ranni, Pandalam, Kuttanad, Malappuram, Aluva, Chalakudy, Thrissur, Thiruvalla, Eraviperoor, Vallamkulam, North Paravur, Chellanam, Vypin Island and Palakkad. All 14 districts of the state were placed on red alert. According to the Kerala government, one-sixth of the total population of Kerala had been directly affected by the floods and related incidents. The Indian government had declared it a Level 3 Calamity, or "calamity of a severe nature". It is the worst flood in Kerala after the great flood of 99 that took place in 1924.
35 out of the 54 dams within the state were opened, for the first time in history. All five overflow gates of the Idukki Dam were opened at the same time, and for the first time in 26 years 5 gates of the Malampuzha dam of Palakkad were opened. Heavy rains in Wayanad and Idukki caused severe landslides and had left the hilly districts isolated. The situation was regularly monitored by the National Crisis Management Committee, which also coordinated the rescue and relief operations as the dam got opened it has disrupted many lives living nearby.
With the recurrence of flood events in the state in the subsequent years, several studies which ensued explain the manifestation of westward-propagating high frequency tropical atmospheric waves of characteristic phase speed of nearly 12 m/s, which originated near east equatorial Indian Ocean or tropical West Pacific and travelled to the east coast of Africa, and coincide with the same period of extreme rainfall events over Kerala. Moreover, the waves appeared as cyclonic and anti-cyclonic circulations trapped to the equator, which dilated the wind field and transported moisture as it propagated. The waves not only stimulated convection along its trajectory, but also ensured sufficient moisture availability. Therefore, the convective activities which intensified in the mid-troposphere, were the direct consequence of the equatorially-trapped high frequency waves, which played a significant role in driving the recurrent anomalous precipitation in the South Indian state.
Causes
The southwest monsoon was in 23% excess in Kerala in the year 2018, with August of that year seeing rainfall 96% above normal. On mid-evening of 8 August, Kerala received heavy rainfall which was 116% more than the usual, resulting in dams filling to their maximum capacities. In the proceeding 48 hours, the state received of rain. Almost all dams had been opened since the water level had risen close to overflow level due to heavy rainfall, flooding local low-lying areas. For the first time in the state's history, 35 of its 54 dams had been opened. One reason is believed to be the levelling of wetlands. The deluge has been considered an impact of global warming.