Representational image

(Aniruddhasingh Dinore/BCCL Nagpur)

For India, June marks a seasonal change where the summer’s excruciating warm and dry conditions get replaced by the pleasant, wet weather triggered by the arrival of the southwest monsoon. As the month goes on, more and more states begin to get drenched by the monsoonal rains, starting from the southernmost tip of Kerala around June 1 to the northernmost parts of the Western Himalayan Region by June end.

June 2022, however, has been slightly unusual in terms of the precipitation it has seen. Between June 1 and 29, all parts of India except the eastern-northeastern region recorded below-average rainfall. India as a whole registered just 141.7 mm rainfall — a 10% deficit compared to the 157.7 mm long-period average (LPA). Listed below are their exact recorded figures and their deviations from the norms.

  • East and Northeast India: 382.2 mm rain recorded — a 21% excess of LPA 315.8 mm
  • South India: 132.9 mm rain recorded — a 14% deficit of LPA 154.9 mm
  • Central India: 109 mm rain recorded — a 33% deficit of LPA 161.9 mm
  • Northwest India: 58.6 mm rain recorded — a 20% deficit of LPA 72.9 mm

But what has led to this below-par monsoon performance in the opening month? According to The Weather Company’s senior meteorologist Takahisa Nishikawa, the following three factors are mainly to blame.

1. Below-average surface temperatures in the Arabian Sea

(Australian Bureau of Meteorology)

The surface temperatures across the Earth’s seas and oceans rarely remain stable. Take the Indian Ocean for example — every few years, its surface temperatures ‘swing’, with its western half getting alternately warmer and then colder than the eastern half.

This oscillation, technically referred to as the Indian Ocean Dipole (IOD), has a notable impact on the Indian monsoon. The IOD is said to be in an active or positive phase when the western part of the ocean is warmer than the east. During this phase, the greater-than-average sea-surface temperatures in the region result in greater precipitation in the western Indian Ocean region, including mainland India.

The IOD was last positive in 2020, and at present, it is neutral and approaching a negative phase. Due to this very fact, the sea-surface temperatures in the Arabian Sea have remained lower than average. This, in turn, has diminished the energy resources for the southwest monsoon by decreasing the moisture supply and effectively led to the below-average precipitation across India through June.

There could be more bad news. Nishikawa adds that the negative phase of the IOD may begin from July onwards, with the peak expected in September. If these projections hold, the ongoing trend of below-normal monsoon rainfall may continue throughout the season for some parts of the country.

2. MJO pulse staying away from India

Phase diagram showing the evolution of the last 40 days of observations along with the 15-day operational GFS forecast. Blue line is the operational GFS forecast with the green line (Ensemble Mean GFS) displayed for comparison. Thick (thin) lines refer to week 1 and week 2 respectively.

(NOAA/ National Weather Service)

The Madden-Julian Oscillation (MJO) is an oceanic-atmospheric phenomenon most prominent in the Indian and Pacific Oceans. It is defined as an eastward moving ‘pulse’ of clouds, rain, winds and pressure near the equator that typically recurs every 30 to 60 days, bringing significant fluctuation in tropical weather in weekly to monthly timescales.

As the MJO moves from west to east, it causes more cloudiness, rainfall and even storminess in the enhanced convective phase and more sunshine and dryness in the suppressed convective phase. Naturally, its arrival in the Indian Ocean during the monsoon season brings along good rainfall over the Indian subcontinent.

But between early to mid-June this year, the MJO remained closer to Africa and away from India, effectively resulting in below-average countrywide precipitation during the start of the monsoon, Nishikawa explained.

It entered the Indian Ocean only towards the end of the previous week (around June 24) but is expected to move away once again by the beginning of July.

3. Boreal heat movement

The third reason can be attributed to Boreal Summer Intra-Seasonal Oscillation (BSISO). While the term sounds very complicated, it describes the simple movement of convection (heat) from the Indian Ocean to the western Pacific Ocean. This movement occurs roughly every 10 to 50 days during the monsoon season, and is representative of the monsoon’s ‘active’ and ‘break’ periods.

Similar to the MJO, the BSISO is also divided into phases that represent the location of the BSISO convective centre. The closer this convective centre is to India, the better it fuels the country’s monsoon activity.

Its impact on the Indian monsoon is the highest when it passes through Phase 3-5. But this month, the BSISO didn’t begin transitioning to Phase 3 until June 23, thereby contributing to the drier nature of monsoon during the first half of June 2022.

To add to it, forecasts indicate that the BSISO may directly transition to phase 8 without passing through phase 4-5, and this could result in below-normal precipitation across India for the next few weeks as well.

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