According to the Centre for Monitoring Indian Economy (CMIE), India received quantitatively adequate southwest monsoon showers till August 17. The season cumulative rainfall figure so far stands 9.5% above normal. Monsoons showers during the critical kharif planting period of July and August also looks impressive. In the last seven weeks, only the week ending August 2 recorded deficient rainfall, while the remaining weeks saw either normal or excess rainfall.
The distribution of rain geographically, however, has been far from normal.
Of the 703 district for which data is available, a total of 236 districts (34% of geographical area) have received normal monsoon rainfall, as per data from the India Meteorological Department (IMD). The CMIE said this area accounts for less than one-fourth of the gross cropped area.
Till August 17, around 36% of India received large excess or excess rain, and 31% received large deficient or deficient rain.
In comparison, 36% of the country’s geographical area received normal monsoon rainfall in 2021, 16% received deficient rain and 48% received excess rain. No area received large excess or large deficient rain last year.
This year, however, 12% of the geographical area — mainly Telangana, Karnataka and Tamil Nadu — received large excess rain, resulting in floods and crop damage. Around 4% of the country — mainly Uttar Pradesh, Bihar, and Jharkhand — witnessed large deficient rain.
The cumulative rainfall deficit in these sub-divisions stood in the range of 36%-48% by August 17. Poor rain in this region has affected the progress of kharif sowings, particularly rice.
Northern and eastern states parched
In Gangetic West Bengal, rainfall has been deficient in 10 of the 11 weeks in the season so far.
In neighbouring Jharkhand, the scenario was similar with only two weeks of normal rainfall during the week ending 22 June and the week ending 17 August.
In the agrarian state of Uttar Pradesh, the western region was better positioned with five weeks of normal monsoon showers. Rainfall was either deficient or scanty in the remaining seven weeks. This region is known as the grain and sugarcane basket of Uttar Pradesh. The sub-division of eastern Uttar Pradesh received normal rainfall only in two weeks this season, as per the CMIE.
Southern and western states inundated
On the flipside, rainfall has been in excess in the southern peninsula. The region has seen incessant rains since the beginning of July 2022. This has taken a toll on kharif cultivation in most of the southern states.
Cumulative rainfall in Telangana and Tamil Nadu was in substantial excess. It was over 60 per cent above normal. Telangana was subject to floods in July 2022 that led to widespread damage to infrastructure and also affected kharif sowings in the state. The state has been subject to extreme weather this season with excess rainfall in six weeks, deficient rains in four weeks and normal rains in one week.
The rainfall pattern in Karnataka has been similar. The state has seen excess rainfall for most part of July and the first-half of August. Cumulative rainfall in Coastal Karnataka was 5% above normal. In south interior Karnataka and north interior Karnataka, monsoon rainfall was 54% and 44% above normal, respectively.
Western states of Gujarat, Maharashtra and Rajasthan have also received excess rainfall.
The new normal
Before the onset of monsoon this year, the IMD reduced the benchmark to define normal southwest monsoon rainfall to 868.6 mm from the previous 880.6 mm on the basis of availability of fresh data from its network of rain gauges across the country.
The new all-India rainfall normal was calculated on the basis of rainfall data over a 50-year period from 1971-2020 and is being used as the benchmark to measure rainfall in the country.
The IMD issues weather forecasts and summaries in terms of departures from the normal, which is a long period average (LPA) of rainfall received over a 50-year period. The ‘normal’ rainfall or the LPA is updated every 10 years. The last update of the LPA was delayed and done only in 2018. Till then the weather office used the LPA of 1951-2001, which was 89 cm, as the benchmark to measure rainfall.
IMD director-general Mrutyunjay Mohapatra said the definition of the LPA has to be updated every decade as per the international practice.
“We take into consideration various aspects. One of them is the climate variability that changes over the period of time. Second, the number of rain gauge stations increases over the period of time giving us more data that is uniformly distributed. So, it (forecast) becomes more realistic and also caters to requirements of smaller regions and specific locations,” he said.
The previous update had taken place in 2019, after a delay of seven years as gathering of data and analysing it took time, he said.
“We have been able to update the new normals within two years as we now have introduced automated processes of data reception, data delegation and calibration of instruments,” Mohapatra said.
Dry and wet epochs
Mohapatra attributed the gradual decrease in the average rainfall to natural multi-decadal epochal variability of dry and wet epochs of all India rainfall.
“Presently the south-west monsoon is passing through a dry epoch which started in the decade of 1971-80,” he said.
According to Mohapatra, the decadal average of all India south-west monsoon rainfall for the 2011-20 decade is -3.8% from the long-term mean.
“The next decade i.e. 2021-30 will come closer to normal and the south-west monsoon is likely to enter into the wet epoch from the decade of 2031-40,” he said.
The new all India annual rainfall normal, based on the 1971-2021 data, has been fixed at 1160.1 mm compared to the earlier normal of 1176.9 mm based on the 1961-2010 data.
Southwest monsoon rainfall, spread across the months of June-September, contributes 74.9% to the annual rainfall, while the pre-monsoon rains – March-April-May – contributes 11.3%.
Post monsoon rainfall – October, November, December – contributes 10.4% to the annual rainfall, while winter rains in January and February contribute 3.4% to the yearly rainfall.
The new rainfall normal has been computed using rainfall data from 4,132 rain gauge stations distributed across 703 districts of the country.
(With inputs from CMIE and agencies)