In the just concluded South West Monsoon 2021, India received 874.6 mm rainfall, about 99.32% of the Normal SW Monsoon rainfall or just 0.68% less than the normal SW Monsoon rainfall of 880.6 mm as per India Meteorological department. This rainfall will now be categorised as normal rainfall though till the beginning of Sept 2021, the rainfall at national level was 10% below normal. The massive 34.96% surplus rainfall in Sept 2021, thanks to a number of circulations contributed from the Bay of Bengal, ending with Cyclone Gulab and now possibly Cyclone Shaheen has contributed to wipe out the deficit.
In SW Monsoon 2020, the rainfall was 956.7 mm, or about 8.74% above normal and in SW Monsoon 2019 it was 10.4% above normal. The district wise, state wise rainfall figures for June 2021, June-July 2021 and June-Aug 2021 are given in separate articles with maps. Similarly figures for High Rainfall events in June 2021, July 2021, Aug 2021 are given in separate articles.
The SW monsoon is now expected to start withdrawal from Oct 6, 2021, as per IMD forecast. This withdrawal is likely to be second delayed since 1960. In 2019 the withdrawal started on Oct 9. IMD has also predicted a normal winter monsoon. The probabilistic rainfall forecast for winter monsoon in south Peninsular India shows that all five meteorological subdivisions (Tamil Nadu, Coastal Andhra Pradesh, Rayalaseema, Kerala and South Interior Karnataka) of the region are most likely to get ‘normal’ rainfall. Its onset may happen towards the second half of October.
On Oct 25, 2021, IMD declared that the SW Monsoon has entirely withdrawn from the country on Oct 25, 2021. This is the 7th most delayed withdrawal since 1975: The southwest monsoon had completely withdrawn from the country on Oct 28 2020; Oct 25 in 2017; Oct 28 in 2016; Oct 29 in 2010; Oct 25 in 2000 and Oct 27 in 1975.
However, the SW Monsoon has not even started withdrawing from any part of India till Sept 30, 2021, as we write this. However, all the rainfall from now on (i.e. after 0830 hours on Sept 30 2021) will be counted in Post Monsoon season in IMD accounts.
The month-wise distribution of rainfall during the SW Monsoon 2021 was as follows.
|June 2021||July 2021||Aug 2021||Sept 2021||SW Monsoon 2021|
Source: IMD; rainfall figures in mm.
As we can see from the table above, while the monsoon rainfall figure of 99.32% of normal rainfall seems to suggest normal rainfall, in reality, the rainfall varied widely across the four m.. The IMD should not be content that it got its overall prediction right but must analyse how its models could be improved to forecast shortfall as well as excess rains.onsoon months. There has been similar wild variation spatially and within the monsoon months, but we do not have an index of rainfall distribution that captures these variations. What we need is a more detailed, nuanced index of rainfall that will not only capture the quantum of rainfall as it does today, but also the temporal and spatial distribution of rainfall across the monsoon. This will give a better picture of the monsoon rainfall and would also help us understand how this index is changing.
An EDITORIAL in THE HINDU on October 6, 2021 said: “Monsoon 2021 capped a rare three years of healthy rain. In 2020, India received 109% of the long period average (LPA) and in 2019, 110% of the LPA and not since 1996, 1997 and 1998 has India got three consecutive years of normal or above normal rain.”
IndiaSpend wrote on Oct 11, 2021: “Marked by extreme localised rainfall events, an unusually dry August and an unusually wet September, the summer monsoon in 2021 kept India guessing, even on its way out… The IMD should not be content that it got its overall prediction right but must analyse how its models could be improved to forecast shortfall as well as excess rains… The incidence of localised extremely heavy rainfall events in July and September, especially on the western coast, were among the highest in the past five years… At a 24% deficit, 2021 saw the first August drought since 2009… September 2021 was different, recording surplus rainfall of 35 percentage points, the second highest rainfall in September in the last 28 years, after only 2019… “Maharashtra bore the brunt of extreme rain events this year,” R.K. Jenamani, senior scientist with the IMD’s National Centre for Medium Range Weather Forecasting in Noida, told IndiaSpend. “The Raigad floods caused a lot of damage. We have never seen Mahabaleshwar receiving more than 500 mm rain for two days in a row. That one week’s rainfall in the Konkan-Goa belt [in July] made up a big part of our total seasonal rainfall.”… The Ministry of Earth Sciences’ first ever climate change assessment for the Indian region, released in 2020, said that monsoon rainfall had declined by around 6% from 1951 to 2015, with notable decreases over the Indo-Gangetic plains and the Western Ghats.”
State wise Rainfall As we can see from the IMD map above, in the four month long South West Monsoon 2021 concluding on Sept 30, 2021, out of 37 States and Union Territories (UTs), Five had Excess (Actual rainfall 20-59% above normal), 22 had normal (Actual rainfall 19% below normal to 19% above normal), Nine had deficit (Actual rainfall 20-59% below normal rainfall) and one (Manipur) had Large Deficit (Actual rainfall over 60% below normal) in rainfall. The states & UTs in Excess rainfall category were: Telangana, Haryana, Delhi, Andaman & Nicobar Islands and Dadar & Nagar Haveli. Telangana had the highest surplus % at 39%. Ladakh had the lowest rainfall at 21.9 mm. Goa had the highest rainfall at 3125.1 mm.
Sub Division wise rainfall IMD divides India into 36 meteorological divisions (the logic of many of them is questionable). As we can see from the IMD map of Sub Division wise rainfall above of SW Monsoon 2021, 10 sub divisions had Excess rainfall, 20 had Normal rainfall and 6 had deficit rainfall. The 30 sub divisions having normal or above normal rains cover 83% of Indian territory. Konkan and Goa had the highest rainfall at 3559.8 mm and W Rajasthan had the lowest at 317.5 mm rainfall. Marathwada had the highest surplus rainfall % at 48%. NMMT (Nagaland, Manipur, Mizoram, Tripura) had the highest deficit rainfall % at 32%.
River Basin wise Rainfall As we can see from the IMD’s river basin wise rainfall map above, IMD also reports river basin wise rainfall. However, as we have been noting in the past, this reporting remains rather callous and inadequate, unfortunately, though IMD would know that it is much more important to provide accurate figures of river basin wise and sub basin wise rainfall figures.
This is clear from the map, where was can see that IMD reports NO RAIN in whole of the four month long monsoon 2021 in several river basins: Upper Brahmaputra, Imphal and others, Nagvati, East flowing rivers between Godavari and Krishna, East flowing rivers between Krishna and Pennar. THIS IS AN IMPOSSIBILITY, looking at the district wise rainfall in these areas in the maps below, among others. This kind of situation keeps repeating year after year. This is the clearest evidence of IMD’s devil cares attitude in reporting river basin wise rainfall. IMD also reports NO DATA in several basins including: Jhelum, Upper Indus.
We shall be reporting more details about the river basin wise rainfall in a separate article as we did in 2020 and earlier years.
Bar charts for daily rainfall IMD also provides bar charts for All India and regional rainfall figures that give comparison between daily actual and normal rainfall for each of the respective regions as can be seen below.
In the All India bar chart, as we can see, the monsoon started with surplus rainfall by third week of June, but the rainfall then fell and there was deficit in early July. This deficit was bridged by some high rainfall days in third week of July. However, in August the deficit was much higher, which was finally bridged by the high rainfall in September 2021.
In Northwest India, there was massive, upto 64% surplus till mid June, which then grew to huge 15 deficit by mid July. This deficit was wiped out by early August. But the deficit thereafter grew back to upto 14% by around Sept 10. This was significantly wiped out by Sept 30, with season ending with deficit of 4%.
In Central India, the deficit in July grew upto 7%, in August upto 14%, but the season ended with surplus of 3% as can be seen from IMD bar chart below.
In East and North East India, the season ended with highest deficit among all regions at 12%. The deficit has remained around that level since mid August. This is more due to the deficit in North East India rather than East India.
In South Peninsula, the monsoon ended with the highest surplus among all regions, at 11%. The surplus had in fact grown to 22% by around July 28, but dropped to around 3% a month latter and then grew to 11%. Notably, the rainfall has remained in surplus zone in South Peninsula throughout the monsoon.
DISTRICT WISE STATE WISE RAINFALL
NORTH INDIA: Jammu & Kashmiar
NORTH EAST INDIA
Karnataka In Karnataka, SW monsoon ended with 8% deficit as per Karnataka State Disaster Management Authority.
The rainfall map of KSDMA is somewhat different than that of IMD, as we can see below. The deficit was at its peak of 47% at the end of August, the August deficit was highest in four years. The malnad region got 1284 mm rainfall as compared to normal rainfall of 1556 mm, 18% deficit. The coastal region received 2692 mm, compared to normal rainfall of 3101 mm, 13% deficit. The North and South Interior regions received 4% below normal rains. The arid Kolar region received the highest rainfall in in 61 years, at 621 mm, compared to normal rainfall of 398 mm.
Andaman & Nicobar Islands
Daman & Diu
Dadar and Nagar Haveli