Last Year Rainfall In Tamilnadu

[Kristy Suzuki]

Duringthe Northeast Monsoon (NEM) of 2023, Tirunelveli, a coastal district in the southern part of Tamil Nadu witnessed record-breaking rainfall of 123.9 cm. This observation was 146% higher than the seasonal average of 50.3 cm, according to data from the Regional Meteorological Centre (RMC).

On December 18, 2023, a weather station in Kayalpattinam in Thoothukudi district, recorded 94.6 cm, the highest rainfall ever witnessed in 24 hours during NEM in Tamil Nadu. This new observation is equivalent to 90% of usual rainfall received by the entire district in a year.

In Tamil Nadu, the average rainfall levels during the southwest and northeast monsoons are 328.4 mm and 443.3 mm respectively. However, a close analysis of the RMC data shows that both the monsoon periods have been erratic in Tamil Nadu since 2015, resulting in extreme weather events such as floods and drought.

Extreme weather events, such as intense rainfall that results in floods or droughts, were predicted by an assessment report from the Intergovernmental Panel on Climate Change (IPCC) in 2021, especially in Asia.

Global warming affects the solubility of gases, including oxygen and the exchange of gases between the ocean surface and the atmosphere. The study warned that it could lead to the natural mixing between nutrient-rich deep waters and the relatively nutrient-poor surface waters of the Bay of Bengal being hindered. More stratification could make this basin far less productive than its western neighbour, the Arabian Sea, it further elaborated.

El Nio is a natural phenomenon that creates a warming effect in the Pacific Ocean periodically. The easterly wind which lifts the clouds hits the Amazon basin with heavy rainfall. Geographically located opposite to the Pacific, it brings dry weather, resulting in droughts in the Indian subcontinent.

The combination of global weather phenomena, El Nino and Indian Ocean Dipole (IOD), involving sea surface temperature variability in the Indian and the Pacific Oceans and their influence on rainfall over the Indian region would continue to prevail, the officials added.

S. Balachandran, Additional Director General of Meteorology, Chennai, said that going by the records since 1901 in Tamil Nadu, rainfall during the northeast monsoon had either been normal or in surplus during 16 occasions when a combination of El Nino and IOD had prevailed.

This year, Tamil Nadu has had normal southwest monsoon as IMD considers September as the month that it officially ends. Wet cover that persisted for many days in September had helped the State scrape through with 8% more rain than average this year.

Mr. Balachandran noted that this southwest monsoon ended in complete contrast to last year. The State had received 45% surplus rain during the previous monsoon. While there was good rain between June and August last year, this year, most of the rainfall occurred in September.

Similarly, Chennai was among the districts that received surplus rain this season. It received 74% in excess of its average of 44.8 cm. Last year, it received only normal rain during the southwest monsoon. A good MJO and development of convective activity in September had led to good monsoon. Meenambakkam received 94.6 cm of rain for the season, one of the highest amount received in the past few decades. The department has forecast wet weather to continue over the State till October 6.

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From October to December each year, a very large area of south India, including Tamil Nadu, the coastal regions of the Andhra Pradesh and the union territory of Puducherry, receives up to 60 percent of its annual rainfall from the northeast monsoon (or winter monsoon). The northeast monsoon is the result of the annual gradual retreat of monsoonal rains from northeastern India. Unlike during the regular monsoon, rainfall during the northeast monsoon is sporadic, but typically far exceeds the amount produced by the regular monsoon by up to 90 percent. This excessive rainfall can be exacerbated by an El Nio of order of the magnitude which has since been evaluated to every year, such as 2015.[20]

The coastal districts of Andhra Pradesh usually bear the brunt of heavy rains that occur during the northeast monsoon; with numerous river systems and wetlands, Puducherry and eastern Tamil Nadu are prone to flooding.[20] The city of Chennai alone experienced five major floods between 1943 and 2005, with the 1943, 1978 and 2005 floods causing particularly severe damage.[21] In addition, unplanned and often illegal urban development has led to many wetlands and natural sinks being built over; this, along with ageing civic infrastructure and poorly designed drainage systems, has resulted in an increased frequency of severe flooding.[20]

Though rainfall from the earlier low-pressure system ended on 24 November, another system developed on 29 November, bringing additional rain and the India Meteorological Department predicted heavy rainfall over Tamil Nadu until the end of the week.[31][32] On 1 December, heavy rains led to inundation in many areas of Chennai.[33] By afternoon, power supplies were suspended to 60% of the city while several city hospitals stopped functioning.[34] The same day, Chief Minister of Tamil Nadu Jayalalithaa announced that, because of the continued flooding and rains, half-yearly school examinations originally scheduled for 7 December would be postponed until the first week in January.[35] For the first time since its founding in 1878, the major newspaper The Hindu did not publish a print edition on 2 December, as workers were unable to reach the press building.[36] The Southern Railways cancelled major train services and Chennai International Airport was closed until 6 December.[34]

Chennai was officially declared a disaster area on the evening of 2 December.[29] At the MIOT Hospital, 14 patients died after power and oxygen supplies failed. With a letup in rainfall, floodwaters gradually began to recede in Chennai on 4 December, though 40 percent of the city's districts remained submerged and safe food and drinking water remained in short supply.[37] Though relief efforts were well underway across most of the area by 3 December, the lack of any coordinated relief response in North Chennai forced thousands of its residents to evacuate on their own.[38] As intermittent rains returned, thousands of displaced residents from Chennai, Kancheepuram and Tiruvallur districts attempted to flee the stricken region by bus or train and travel to their family homes.[39] Chennai International Airport was partly reopened for cargo flights on 5 December, with passenger flights scheduled to resume from the following morning.[40] By 6 December, rescue efforts had largely concluded and relief efforts intensified, with the Chennai Corporation beginning to disburse relief packages.[41] Mobile, banking and power services were gradually restored; fuel and food supplies were reaching their destinations, the airport had fully reopened and rail services slowly resumed. Many city neighbourhoods, however, remained flooded with some lacking basic necessities due to the uncoordinated distribution of relief materials. With the city slowly beginning to recover, state and national health officials remained watchful against disease outbreaks, warning that conditions were right for epidemics of water-borne illnesses to occur.[42] Chennai Corporation officials reported at least 57,000 homes in the city had suffered structural damage, mostly those of working class. State housing boards said they would conduct safety inspections of both public and residential buildings.[43] After being closed for the past month, schools and colleges across the affected districts began to reopen from 14 December.[44] Relief operations were largely wound up by 19 December.[45]

After Chennai district, Cuddalore district was among those most severely affected by the flooding. Six of the district's 13 blocks suffered extensive damage during the floods in November.[51] The resumption of heavy rainfall from 1 December again inundated the Cuddalore municipality and the district, displacing tens of thousands of people.[52] Rains continued through 9 December.[53] Despite the state government and individuals sending rescue teams and tonnes of relief materials to the district, thousands of those affected continued to lack basic supplies due to inadequate distribution efforts; this resulted in several relief lorries being stopped and looted by survivors.[53][54] Large swaths of Cuddalore city and the district remained inundated as of 10 December, with thousands of residents marooned by floodwaters and over 60,000 hectares of farmland inundated; over 30,000 people had been evacuated to relief camps.[53][55]

Puducherry sustained relatively minor damage in November as the depression largely remained offshore; some trees were downed and several banana and sugarcane plantations at Kuttchipalayam were severely damaged.[61] Puducherry reported receiving 55.7 mm of rainfall over the 24-hour period from 14 to 15 November. Water entered several houses in low-lying areas, while three houses collapsed in Uppalam. Mudaliarpet, parts of Rainbow Nagar, Muthialpet, Krishna Nagar and Lawspet Main Road were inundated, along with portions of roadways near Karuvadikkuppam and the Shivaji statue on the ECR, causing traffic problems. Several roads were badly damaged, hindering motorists, while some members of the public took the initiative to begin clearing areas of water without directions from the government. Chief Minister N Rangasamy stated the official machinery had been readied in preparation for any flooding, while local administration officials closed all schools and colleges in Puducherry and Karaikal districts on 16 November, anticipating further rainfall.[62]

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