According to India Meteorological Department (IMD), during the just concluded Post Monsoon Rainfall for 2021, that included rainfall during Oct-Dec months, India received 177.7 mm rainfall, 43.54% above normal rainfall of 123.8 mm. In the same period last year, India received 124.6 mm rainfall, 0.64% above the normal rainfall. As per IMD[i] definition, the rainfall was in surplus category.
This three-month period from Oct 1, to Dec 31 includes the North East Monsoon that mainly affects parts of South India including Tamil Nadu, Puducherry, Rayalseema, parts of Karnataka and Kerala. However, since the South West Monsoon had not yet withdrawn from the country by Sept 30, a significant proportion of the rainfall in October was contribution of the SW monsoon. This was similar situation in 2019 and 2020[ii] too.
In fact as per IMD Press Release of Oct 28, 2020[iii], SW Monsoon withdrew from India only on Oct 28, 2020 and NE Monsoon set in on the same date.
The period also includes the rainfall that most of North India gets from western disturbances, but that contribution has been below normal this year. La Nina has also made some contribution in increasing the rainfall significantly above normal, which was not the case last year.
In Post Monsoon season of 2019, India received 160 mm rainfall[iv] in this season, 29% above normal, when 2019 was not a La Nina year.
Monthly rainfall The distribution of rainfall for the three months of Post Monsoon 2021 season as per IMD figures is as follows. While the monthly normal and actual rainfall decreases as we go from October to December, the % surplus also decreases and turns into slight deficit by December 2020. There is no evident impact of La Nina here.
|Months||Actual rainfall, mm||Normal rainfall, mm||% departure|
|Post Monsoon 2021||177.7||123.8||43.52|
Major unknown One major unknown, here is that it is not clear if IMD’s these reported figures include the contribution from snowfall and if so what is the contribution of snowfall. It is not even known looking at the IMD website if IMD even monitors the snowfall figures and if so what are they. We cannot find any reporting of the snowfall figures in any case. This is worrying since snowfall is expected to make a significant contribution during winter months and we seem to be in total dark as to what is the quantum of snowfall in different districts, states, in different months & years.
ALL INDIA: State wise rainfall Fourteen States and Union Territories (UTs) had Large Excess Rainfall (more than 60% above Long Period Average or LPA), 9 had Excess (20-59% above LPA), 6 had normal (19% below to 19% above normal) and 8 states and UTs had Deficit Rainfall (20 to 59% below normal) during Oct Dec 2021 period in India. Here LPA is Long period average, taken as average of the rainfall during 1961-2010. Ladakh had the highest deficit at 56%. Pondicherry had the highest rainfall at 1425.1 mm, way above the 2nd highest rainfall in Tamil Nadu at just above 700 mm. Uttarakhand had the highest surplus % at 263%.
Sub-Division wise rainfall Among IMD’s 36 sub divisions, 16 received Large Excess, 9 received Excess, 6 received Normal, 5 received Deficit rainfall. Like in 2020, Andaman and Nicobar Islands received the highest divisional rainfall at 774.4 mm.
River basin wise rainfall The media generally ignores this, but IMD also reports river basin wise rainfall, which is actually the most important way to report rainfall. But this year too IMD unfortunately has done a rather callous job of it. During Post Monsoon 2021 season, IMD reports ZERO rainfall in several basins: Narmada, Tons, Vaippar-Pamba, Kynchiang, Upper Brahmaputra, Imphal & Others, Barak. This is clearly an impossibility. For two river basins (Jhelum and Upper Indus) IMD had no rainfall data (like was the case in 2019 & 2020)!
STATE WISE DISTRICT WISE RAINFALL: NORTH ZONE: Jammu and Kashmir
EAST ZONE: Uttar Pradesh
NORTH EAST ZONE: Assam
SOUTH ZONE: Telangana
WEST ZONE: Maharashtra
[i] India Meteorological Department (IMD) divides a water year (June 1 to May 31) into four seasons: Monsoon: (June 1 to Sept 30), Post monsoon (Oct 1 to Dec 31), Winter (Jan 1 to Feb 28/9) and Pre Monsoon (March 1 to May 31). For rainfall during all these seasons, IMD’s hydro-meteorological website provides a lot of data on daily basis, including daily district wise, state-wise, sub division wise and river wise rainfall maps among many other weekly, monthly and seasonal products. However, one problem with it is that none of this information is achieved. So if you missed seeing or downloading available data on any date, there is no way to look at it even next day. This is even true of the seasonal rainfall maps, unfortunately.