This year’s monsoon may be normal for the country as whole, but its distribution has been quite erratic – many states are experiencing widespread rain leading to floods and landslides, while some are facing a sizeable deficit, big enough to affect the sowing reason.
While most of northeast India received surplus rain in June, in July and August that dropped drastically. Large parts of north, central and western India were also struggling to cope with poor rainfall in these months.
The tide turned in July and August, when swathes of central, west and south India were deluged. The northern states of Uttar Pradesh (UP), Bihar, and Jharkhand are still struggling to cope with a huge deficiency. However, India on the whole has had normal rains so far.
Slow start in June
If one looks at the Indian Meteorological Department’s (IMD) sub-divisional rainfall map, from June 1-30, Assam and Meghalaya together received 858 mm of rain against their usual quota of about 486.6 mm, i.e., 76 percent more than normal. Such rainfall is considered a ‘large excess’. The two states suffered a series of devastating floods and landslides during this time.
With 727.5 mm of rainfall instead of the regular 455.9 mm, or a 60 percent excess, sub-Himalayan West Bengal and Sikkim was the only other sub-division with large excess rain in June.
The Jammu and Kashmir-Ladakh region (+53 percent), Rayalseema (+47 percent), Tamil Nadu-Puducherry-Karaikal (+56 percent), and Arunachal Pradesh (+37 percent) regions received 'excess rain’ during the same period.
All in all, two of the 36 sub-divisions received large excess rain, while four had excess rain in June. Ten sub-divisions had normal rain - four in the northwest, central, and eastern parts, while the rest were in central and southern India.
Twenty sub-divisions spread across the northern, central and western parts experienced deficient rainfall. East and west UP, Saurashtra and Kutch, Gujarat , Kerala, and Mahe experienced more than 50 percent deficit.
There were no areas with ‘large deficiency’ or no rain in June.
Rainfall deficiency ranging from -99 to -60 percent is considered ‘large deficient’ in Met (meteorological) parlance; -59 to -20 percent is ‘deficient’, and -19 to +19 is 'normal’. ‘Excess’ ranges from +20 percent to +59 percent. Anything above 60 percent or more is ‘large excess.’
A shift in July-August
From July 1-31, there was a gradual shift in the distribution. Eight sub-divisions across the northeast, Sikkim, UP, Jharkhand, and West Bengal – comprising 21 percent of the sub-divisional area – had deficient rain.
Assam and Meghalaya saw a significant swing from a 76 percent excess in June to a 47 percent deficit in July. Bihar, which got normal rain in June, was the only sub-division with large deficient rainfall (-60 percent) in July.
Nineteen Met sub-divisions across northwest, central and south India – comprising 54 percent of the sub-divisional area – recorded either large excess or excess rain, leading to flash floods in many states.
Eight sub-divisions spread across the northern, central, southern, and eastern parts had normal rain in July.
From August 1-23, things got better for Jharkhand and Gangetic West Bengal. These sub-divisions recorded excess and normal rain, respectively.
In the northeast, the dry spell continued in Assam and Meghalaya, which recorded a 49 percent deficit. With a minus 60 percent shortfall, Arunachal Pradesh reported large deficient rains.
The Gangetic states of UP and Bihar had a large deficit, with east UP recording a -38 percent deficiency. West UP had -45 percent and Bihar -48 percent deficiency in August, affecting paddy sowing in these states as well as the northeast.
Punjab, Haryana-Chandigarh-Delhi, and Marathwada, which had good rains in July, recorded -58 percent, -43 percent, and -37 percent deficit, respectively, in August.
Of the rest, 12 sub-divisions recorded excess, four reported large excess, and 10 had normal rain in August. West Madhya Pradesh (MP) and west Rajasthan had 76 and 73 percent excess rain, respectively.
Despite this wide variation, India as a whole registered normal rainfall with a -8 departure in June, +17 percent in July and a +11 percent departure from August 1-23. From June 1-August 23, India had surplus rainfall of 9 percent, which is considered normal.
A variable pattern
Explaining the monsoon pattern this year, R.K. Jenamani, senior scientist at IMD, said that thus far, the spatial distribution of the rainfall in August has been similar to that of July.
“There was excess rain over peninsular and central India. The areas that recorded deficient rains in July continued to get less rain in August as well. For example, northeast India and parts of north India covering Bihar and UP,” Jenamani added.
Gangetic West Bengal and Jharkhand showed some improvement but were still deficient with -28 to -30 percent below normal rain between June1-August 23, Jenamani said. The deficit was -47 to -49 percent between June 1-July 31.
According to Jenamani, July had four monsoon low pressure systems that moved from the Odisha coast, across central India along the monsoon core zone, and reached south Rajasthan, in over 21 days.
This movement kept the monsoon trough south of its normal position on most dates barring July 28-31, because of which it rained over central and peninsular India, while parts of the north and north-east saw deficient rainfall, he added.
In August, he explained, the wind pattern behaved like July. August also had four low pressure systems, which became a depression for 26 days. That again kept the trough south of its normal position, resulting in decreased rain in parts of the north and northeast.
In fact, this August was the first time since 2005 that such a large number of depressions formed over India, Jenamani said, adding that three of them were over the Bay of Bengal, off the Odisha-West Bengal coast.
Despite the deficit in July-August, Assam-Meghalaya and Arunachal Pradesh overall recorded normal rain from June 1-August 23 on account of the June surplus. The Nagaland-Manipur-Mizoram-Tripura sub-division, however, reported a 25 percent deficit overall, according to IMD data.
Climate change vs. variability
IMD director general Mrutyunjay Mohapatra said that even in a good year, some parts face a deficit while others experience excess rainfall, and this is normal.
“Monsoon variability cannot be attributed to climate change,” Mohapatra told MoneyControl.
Mohapatra, however, said that sudden spells of very heavy rain can be due to climate change, and this has made weather forecasting difficult. “India is a huge country with different features, and variations are natural. The monsoon sees large variations year on year, and within the same year too.”
This year, he said, only UP and Bihar have seen less rain throughout the season.
One has to look at 100 years of data to establish a clear trend, Mohapatra said, adding that the monsoon has been more or less trendless on the whole.
“But some trends have been observed, such as less rain in the northeast and more rain in Rajasthan, Saurashtra and Kutch,” Mohapatra said.
Incidents of heavy rainfall are increasing and those of light rain are decreasing, and need in-depth study, he added.
Explaining the variability and the intense rain patterns, Roxy Mathew Koll, climate scientist at the Indian Institute of Tropical Meteorology, Pune, said rising global temperatures have led to an overall increase in moisture levels.
“This is because warmer air holds more moisture and for a longer time. Hence, it does not rain for a long time, but when it rains, it dumps all the moisture within a few hours or days,” Koll said.
Monsoon patterns have shifted in recent decades, Koll added. The most significant change is that instead of moderate rain throughout the season, we have long dry periods and short spells of heavy rains.
“This causes floods and droughts in the same season, and occasionally in the same region, or in different parts of the country,” Koll said.
In UP, Bihar, and Jharkhand the total rainfall has declined over the decades. This is associated with weakening monsoon winds and circulation, which are not penetrating to the northern-most inland states as earlier, Koll said.
According to Raghu Murtugudde, a professor at the department of atmospheric and oceanic science, University of Maryland, rain distribution is erratic because of a northward shift in the low-level jet, or the south-westerly winds, over the Arabian Sea.
This has produced a deficit over Kerala but excess over northern Maharashtra and Gujarat into Pakistan.
“This shift also explains the deficits elsewhere. But monsoon extremes continue because of global warming. The northeast is getting most of its moisture from the Bay of Bengal,” he said.
Multiple influences on the onset and evolution of the monsoon shapes its behaviour, Murtugudde said, adding that it is not done yet because more weirdness is on its way.
“Because the Arctic is warmer and La Niña is active, withdrawal (of the monsoon) may be delayed and we may get more extremes in September,” he warned.
The uneven distribution and deficiency in some states led to a fall in the sowing of paddy in July. Paddy is one of the main crops of the kharif season from June-October. A fall was reported from Bengal, UP, Bihar, Jharkhand, Odisha, Tripura, and Assam, among others.
As per union agriculture ministry data, as on July 29, paddy had been sown in over 23.15 million hectares (mha). This is 3.55 mha less than 2021, when 26.7 mha was covered.
On August 18, the paddy sowing area increased to 34.37 mha, but was still less than 2021 when 37.46 mha was covered. The normal area under paddy at this time of the year is 39.7 mha.
Group Captain S.N. Mishra, an independent climate change expert, agreed that there was a shortfall in the kharif crop as the rain deficit in some states had impacted paddy sowing.
“However, enhanced rainfall subsequently over the eastern regions, and the storage of surplus water in reservoirs, augurs well for the rabi crop,” he said.
West UP, Mishra said, may end up as the most rainfall deficient subdivision, but it is mostly irrigated through a network of canals and the rabi crop may not be impacted.
Variability is intrinsic to the monsoons, he said, adding that a few regions will always be impacted by either temporal or spatial variability.
Mahesh Palawat, vice-president of meteorology and climate change at Skymet, said there was little chance of the monsoon becoming active over UP and Bihar. Northern Bihar and the UP foothills may witness a few spells from August 26, which may continue on and off till September 5 or 6, Palawat said.
“But I do not think these rains will be enough to boost agricultural output. Continuous rain is ruled out. September may turn out to be deficit for east and northeast India,” he added.