Weather Report: Clear skies in August to affect agriculture

Monsoon 2023 started with a weak onset in the country during June but bountiful rains in July covered the deficiencies and placed the pan India seasonal rainfall at +7 per cent by month end. Now since the beginning of August, pan-India rains have seen a significant reduction as the monsoon takes a break. [caption id=“attachment_12994572” align=“alignnone” width=“657”] A satellite imagery of Sunday afternoon show weak and mere cloud cover over India[/caption] One might wonder why the monsoon would take a break? Theoretically the atmosphere is a fluid after a period of time absolute saturation is achieved and it tries to adjust with a phase of dry weather, Monsoon has active and break phases as its seasonal features. How does the monsoon take a break? The synoptic features influencing the entire monsoon track and changes in them result in increase or reduction in rains. • The low pressure area that forms up in the Bay of Bengal drives rain in the core monsoon zones ie central and western India and some parts of peninsula, a pause in the formation of low pressure areas results in dry weather conditions over large parts of the country. • The monsoon axis decides the movement of low pressure systems from Bay of Bengal to interiors of the country, when the eastern of monsoon axis or say trough is not connected with low pressure it starts shifting towards the foothills of India, once the trough establishes over Himalayas rains reduces across plains of north India, technically 80 per cent of country faces dry weather conditions under such scenario and rais are mainly restricted to Himalayan foothills and east and north east India. August show has been poor across country, pan India rainfall till 12 August stands at 73.4 mm against the normal of 106.8 mm the departure from normal stands at -31 per cent, the matrix of seasonal rains stands at 540.4 mm against the normal of 552.6 mm departure turns negative at -2 per cent for the period of 1st June till 12 August 2023, giving a fair dent on good numbers from July. [caption id=“attachment_12994582” align=“alignnone” width=“732”] Rainfall statistics of monsoon rains 2023 so far[/caption] El Nino show started, does it mean longer breaks in monsoon? The ENSO conditions have strong impact over India, El Nino years if dominates relates to longer spells of dry weather during the core monsoon months, but interestingly there has been regional distribution of its impact as well studied over the years, as per the latest study done by the team of scientists in IITM Pune, it has been reported a significant change in El Niño–monsoon relationship over the north, central, and south India. They find that while the El Niño–monsoon relationship has stayed moderately strong and stable for south India, it has become exceptionally stronger over time for north India, while it has considerably weakened and become non-existent over the central Indian region (core monsoon zone) in the recent decades. El Niño–monsoon relationship The Indian monsoon has waxed and waned over time. The year-to-year fluctuations of the monsoon are largely modulated by the fluctuations in ocean temperatures in the Pacific. These oscillations in the Pacific Ocean are dominated by the El Niño and La Niña, the warm and cool water phases in the central-east Pacific, known as the El Niño Southern Oscillation (ENSO). Generally, an El Niño event weakens the trade winds that blow across the Pacific. These trade winds are connected to the moisture-laden monsoon winds over India, and thereby dampens the monsoon too, reducing rainfall over the Indian subcontinent. Historically, at least half of the El Niño years were monsoon droughts (where the All-India monsoon rainfall is less than 10 per cent of the long-term average) [caption id=“attachment_12994592” align=“alignnone” width=“760”] Pan India monsoon performance in the period of 1871 till 2020 as per ENSO conditions[/caption] Regional variability over time The ENSO impact over the Indian subcontinent is not the same everywhere. The relationship between ENSO and monsoon has not remained the same throughout the period from 1901 to the present. We notice that the ENSO–monsoon relationship started getting stronger from 1901 to 1940, became stable from 1941 to 1980 and then the relationship has weakened in the recent period (1981 onwards). These changes in the ENSO–monsoon relationship are regionally non-uniform. Over south India, there is no considerable variation in the ENSO–monsoon relationship. Whereas over north India the ENSO–monsoon relationship is becoming strong in recent decades. On the contrary, association between the rainfall over central India (core monsoon zone) and ENSO has diminished in the recent decades. The monsoon rainfall is also influenced by the strength of the monsoon trough and related changes in monsoon depressions. The monsoon trough and depression related variability has emerged as the primary cause of rainfall variability over central India, surpassing the dominance of ENSO. For the rainfall over south India, the influence of ENSO and strength of monsoon trough and depressions have been consistent over the entire period. Over north India, rainfall variability is increasingly dependent on ENSO, while the role of the monsoon trough and depressions is decreasing. This may be due to the decreasing strength of the monsoon due to Indian Ocean warming, and the weakening reach of the monsoon depressions into the north Indian region in recent decades. [caption id=“attachment_12994632” align=“alignnone” width=“988”] The correlation of El Nino with regional rainfall distribution in India during 40 years to data sizing[/caption] What does the monsoon performance look like in the remaining days of the season? The answer is Poor, the way monsoon break has kick started in the August and two weeks have nearly passed the rainfall anomaly has gone negative, as per the weather models there is no significant rain expected in any region of the country for nearly next two weeks, this is haunting as seasonal rainfall anomaly by the month end might surpass over -8 per cent to -10 per cent which is currently at -2 per cent, the delta becomes hard to cover specially in the month of September where climatology wise rains on average are lower. With El Nino on the front seat, Good rains are now under the cloud cover of El Nino and the stress on agriculture will start becoming intense as August progresses with clear skies or empty clouds. The writer, better known as the Rohtak Weatherman, interprets and explains complex weather patterns. His impact-based forecasts @navdeepdahiya55 are very popular in north India. Views expressed in the above piece are personal and solely that of the author. 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