On almost all days in June so far, North and Northwest India have experienced ‘heatwave’ to ‘severe heatwave’ conditions. The southwest monsoon that made an early onset over Kerala has advanced until Maharashtra, but maximum temperatures in the plains of North India have sustained around 45-47 degrees Celsius.
The June-September southwest monsoon brings more than 70% of India’s annual rainfall. Climatologically, the monsoon arrives over the Andaman Sea in the third week of May and advances into the mainland through Kerala, June 1 being the normal date of onset.
It then advances in surges — typically, the progress until central India is fast, after which it slows down. The monsoon normally reaches north Uttar Pradesh, Delhi and neighbourhood areas by the end of June, and covers the entire country by July 15.
An early or timely onset of the monsoon does not guarantee good rainfall or its distribution over the country throughout the four-month season. And a delayed onset does not necessarily mean below-average rainfall for the entire season.
Cumulative rainfall over the country from June to September depends on multiple factors. It also shows natural inter-annual variability, which makes every monsoon different. Alongside the quantum of rainfall, its distribution is also vital.
The India Meteorological Department (IMD) has forecast ‘above normal’ rainfall this season. Quantitatively, it is expected to be 106% of the Long Period Average of 880 mm (1971-2020 data).
The ‘above normal’ rainfall is being attributed mainly to the soon-to-emerge La Niña conditions, which are known to positively influence the Indian monsoon, and a positive phase of the Indian Ocean Dipole (IOD).
The monsoon arrived over the Andaman Sea and Nicobar Islands on May 19, and hit the Kerala coast on May 30, two days ahead of its normal date. It reached over Nagaland, Manipur, Mizoram, Arunachal Pradesh, and parts of Tripura six days early — marking a rare but not-unheard-of simultaneous onset over Kerala and large parts of Eastern India.
After May 30, the monsoon progressed every day, and it had covered Andaman & Nicobar Islands, Kerala, Lakshadweep, Mahé, Tamil Nadu, Puducherry, Karnataka, Telangana, and large parts of Andhra Pradesh and Maharashtra by June 10.
This kept the all-India rainfall positive at 36.5 mm, or 3% surplus as on June 10. Over all these states and UTs, the monsoon arrived three to five days early.
From June 11 onward, the monsoon has remained stagnant, and dry and hot conditions have returned to the Southern peninsula. Over the past week, all-India rainfall has been consistently below average. On Tuesday, it was minus 20% (64.5 mm against normal 80.6 mm).
“Initially, the monsoon came in as a big current but did not bring much rain. This is not a typical monsoon flow, compared to what was expected,” M Rajeevan, former secretary, Ministry of Earth Sciences, said.
On Tuesday, the Northern Limit of Monsoon — the imaginary line indicating the monsoon’s progress — passed through Navsari, Jalgaon, Amravati, Chandrapur, Bijapur, Sukma, Malkangiri, Vizianagaram and Islampur.
The overall deficit is mainly due to states where the onset of the monsoon has been delayed. These include Odisha (minus 47%), West Bengal (minus 11%), Bihar (minus 72%) and Jharkhand (minus 68%) as on Tuesday.
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