Causes
Rainfall from the southwest monsoon was 23% higher than normal in Kerala in 2018, with August seeing rainfall 96% above normal. [19] On the evening of 8 August, Kerala received heavy rainfall which was 116% more than usual[ clarification needed ], resulting in dams filling to their maximum capacities. In the proceeding 48 hours, the state received 310 mm (12 in) of rain. Almost all dams had been opened since the water had risen close to overflow levels due to heavy rainfall, which flooded local low-lying areas. [20] [21] For the first time in the state's history, 35 [14] of its 54 [15] dams had been opened. The deluge is considered an impact of global warming. [22] [23]
Independent scientific studies conducted by hydrology experts from IIT Madras, Purdue University, and IIT Gandhinagar concluded that heavy downpour and dam management resulted in the floods. [24] [25] [26] Based on a computer simulation of flood storage and flow patterns by a team of researchers from IIT Madras and Purdue University, it was found that the devastation wrought by the floods cannot be attributed to the release of water from dams. Further, the scientists added that the odds of such floods were 0.06% and no reservoir management could have considered such scenarios. [25] A hydrology expert from IIT Gandhinagar, Vimal Mishra, identified four major factors for the floods: unexpected above-normal downpour, extreme rainfall events occurring almost across Kerala during the season, over 90% reservoir storage even before the onset of extreme rainfall events, and the unprecedented extreme rainfall in the catchment areas of major reservoirs in the state. [26]
The prime reason for the anomalous rainfall in 2018 is the high-frequency mixed Rossby-gravity waves in the mid-troposphere triggered by the synoptic disturbances of the tropical Pacific. [27] [23] These high-frequency waves manifested as cyclonic and anticyclonic circulations and dilated the wind field to establish zones of convection in the tropics, as they propagated across the Indian Ocean basin. Although the Madden-Julian Oscillation phase with 20-to-40-day period has favored convection in the tropics, the high-frequency mode correlates better with the anomalous precipitation during the intervals of extreme events. [27] [23]
Expert bodies like the Central Water Commission have corroborated the findings by scientists from IIT Madras, Purdue University and IIT Gandhinagar. [28] [29] [30]
A report by Adv. Jacob P. Alex, an advisor appointed by the Kerala high court, alleged that the devastating floods of 2018 were the result of bad dam management by the state government. [31] [32] [33] [34] All 79 dams in the state were maintained with the objective to generate hydroelectricity or irrigation and controlling flooding wasn't their purpose. "The major concern of the dam operators was to maximise reservoir levels, which conflicted with the flood control purpose for which the dams could be utilised. The 'flood cushion' of reservoirs – the storage space earmarked in dams to absorb unanticipated high flows – needed review as per the latest guidelines," Alex wrote in his report. "Sudden release of water simultaneously from different reservoirs, during extreme rainfall aggravated the damage," it said, adding that various alerts—blue, orange and red—had been issued not in accordance with the EAP guideline. "No proper follow-up action and effective precautionary steps (especially for evacuating people and accommodating them in safe location) were taken after issuance of Red Alert," it said. As of August 2024 [update] , the high court of Kerala had not accepted the report. [35]
The government of Kerala argued in the Supreme Court that the sudden release of water from the Mullaperiyar Dam by the Tamil Nadu government was one of the reasons for the devastating flood in Kerala. [11] The Tamil Nadu government rejected the argument, saying that Kerala suffered the deluge due to the discharge of excess water from 80 reservoirs across Kerala, spurred by heavy rains from within the state; It also argued that the flood surplus from the Idukki dam was due mainly to the flows generated from its own independent catchment due to unprecedented heavy rainfall, while the discharge from the Mullaperiyar dam was significantly less. [36] [37]
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