Heavy Rainfall in India in Oct-Nov 2021

India has seen rather heavy rainfall in October and November 2021, with October All India Rainfall being 33% above normal and November rainfall being record breaking 86% above normal. The combined Oct + Nov Rainfall was 48% above normal, and by Dec 7, as we write this, it is already 53% above normal for the period from Oct 1 to Dec 7, 2021.

While lingering South West Monsoon brought large part of the excess rainfall in first half of October, the unusually active North East Monsoon with continuous supply of moisture from Bay of Bengal has been the main reason for the high rainfall since late October. The onset of La Nina has also contributed to this and with La Nina forecast to remain in place till March 2022, we are in for continued wet spell in South India, it seems. IMD has already forecast above normal rainfall in South Karnataka during Dec 2021 to Feb 2022.

All India Rainfall Maps As can be seen from the IMD’s Meteorological division wise rainfall map for North East Monsoon as on Nov 30, 2021, 15 divisions had Large Excess, 12 divisions had Excess, 4 divisions had Normal and 5 divisions had deficit rainfall during Oct-Nov 2021.

The state-wise IMD map shows that 15 states/ Union Territories had Large excess, 9 had Excess, 5 had Normal, 7 had deficit and only Manipur had Large Deficit.

The River Basin wise IMD rainfall map for the same period shows IMD’s callousness in providing misleading picture with several river basins including Narmada, Tons, Vaippar-Pamba and some in North East India showing to have received NO rainfall and NO DATA for several basins in North India.

High Rainfall instances Peninsular India recorded the highest ever rainfall in November 2021 since 1901, said the India Meteorological Department [i] (IMD) while noting that even the ‘heavy’, ‘very heavy’ and ‘extremely heavy’ rainfall events last month were the highest over the last five years. Andhra Pradesh, Tamil Nadu, Puducherry, Kerala and south interior Karnataka received 169% excess rainfall in November while the country witnessed 645 ‘heavy’ (64.5 to 115.5 mm), 168 ‘very heavy’ (115.6 to 204.5 mm) and 11 ‘extremely heavy’ (over 204.5 mm) rainfall events in November. If we look at district wise daily rainfall figures, we see that in November 2021, there were 127 instances when district rainfall was 50-100 mm, 25 instances when rainfall was 100-150 mm, 2 instances each when rainfall was 150-200 and above 200 mm. In October, there were 237, 37, 11 and 3 instances respectively, higher than those in November.

South India IMD figures show that October contributed more rainfall at all India level (100.7 mm, 33% above normal rainfall of 76 mm) compared to November (all India rainfall 56.5 mm, 86% above normal rainfall of 30.4 mm). However, in most of the South Indian states/ meteorological divisions, it as the November rainfall that has been much higher than October rainfall, as can be seen from the table below.

Area	Oct 2021: Actual Rainfall, mm	Oct 2021: Normal Rainfall, mm	Oct 2021: % departure	Nov 2021: Actual Rainfall, mm	Nov 2021: Normal Rainfall, mm	Nov 201: % departure
Rayalseema	146.4	129.8	13	302	70.2	*330*
Tamil Nadu	228	177.2	29	423.1	178.8	*137*
Pondicherry	380.5	262	45	986.3	401.4	*146*
South Interior Karnataka	267.2	141.6	89	212	50.6	*319*
Kerala	589.9	303.4	94	394.5	153.4	*157*
India	100.7	76	33	56.5	30.4	86

Source: IMD’s Daily District wise rainfall bulletins for respective dates

As we can see, both the absolute quantum of rainfall and the % departure in South India is higher in November than October in almost all cases, except the quantum of rainfall in case of Kerala and SIK. Even in these cases, the % departure in November is much higher in November than compared to October.

Karnataka Rainfall highest in 60 years Karnataka received [ii] an all-time high rainfall of 249% excess in Nov 2021. Bengaluru got third highest rainfall, 224 mm, 329% above rainfall in this month, only 1916 and 2015 had higher rainfall.

According to data from the Karnataka State Natural Disaster Monitoring Centre [iii], the State as a whole recorded an actual amount of 322 mm of rainfall as against the normal rainfall of 173 mm during Oct-Nov 2021, with the percentage departure from normal being 87%. This is the highest in the last 60 years. During the two-month period, South Interior Karnataka recorded a 143% departure from normal, which was the highest in the last 60 years, and for November alone too, which was a 293% departure from normal. Coastal Karnataka had 119% more rainfall for the two months, the second highest in 60 years. For November, it was the highest in 60 years with a 311 % departure. Similar was the case with Malnad, where the 113% departure for two months was the highest in 60 years, and 259% departure in November the second highest for the same period. North Interior Karnataka had only a 12% departure in October-November, but for November, it saw 168% departure, the fifth highest in 60 years. “During the northeast monsoon season, the State average rainy days are 10. This year, we had 18 rainy days; South Interior Karnataka had 22 rainy days instead of the normal 12, Malnad 25 instead of 12, and the Coastal region 24 instead of the normal 13 rainy days,” KSNDMC officials said.

The Rainfall map of Karnataka districts for Oct-Nov 2021 rainfall given below from IMD provide district wise rainfall departures for Oct-Nov 2021. As we can see, all the Deficit (two districts), Normal (3), Excess (5) rainfall districts are in North and all the Large Excess Rainfall districts (20) are in the south, with Tumkur having the highest departure at 219% excess rainfall.

Andhra Pradesh The IMD’s rainfall map for Andhra Pradesh shows that like in case of Karnataka, the Deficit (two districts), Normal (5), Excess (2) rainfall districts are all in the North, while all the four Large Excess Rainfall districts (three of Rayalseema and Nellore) are in Southern part of the state.

Tamil Nadu The IMD’s rainfall map for Tamil Nadu shows that out of 38 districts in the state, one district had normal rainfall, 7 had Excess rainfall and 30 had large excess (60% or more above normal). 13 of them had more than 100% above normal rainfall, with Villupuram having the highest excess at 169%. Six districts had above 1000 mm rainfall, with Chennai having the highest rainfall at 1150.2 mm during the two months of Oct-Nov 2021.

Kerala All the 14 districts of Kerala had Large Excess Rainfall in Oct Nov 2021 as we can see from IMD map. Nine of them had excess above 100% and four had rainfall above 1000 mm, with Patanamitta having the highest rainfall (1619.4 mm) and highest departure from Normal (193%).