Last 10 years of southwest monsoon for the Indian sub-continent remained an intriguing story. Between 2012 – 2021, the continent experienced nearly all shades of monsoon. There were 2 droughts (2014 & 2015 ), 3 below normal ( 2012, 2017, 2018 ), 2 normal (2016 & 2021) and 3 above normal (2013, 2019, 2020) seasons. Most contrasting were 2 consecutive years of 2018 & 2019. The year 2018 nearly averted a drought with a seasonal deficiency of -9.4%. The successive year 2019 missed an excess by a whisker and finished with a surplus of 9.96%.
True to its reputation, monsoon continues to be truant. Decoding monsoon remains a challenge as it keeps throwing surprises, both on short and long term basis. 2018 and 2019 not only remained diverse as a season but also were variant in month wise quantum and distribution of rainfall. While 2018 was a good starter and a poor finisher, 2019 had a depressing start and a copious closing.
2018 was an evolving El Nino year. All the 4 Nino indices in the Pacific Ocean mostly remained below the threshold value of + 0.5°C. However, these were blown in to a full fledged El Nino by fall of the year. Warming of equatorial Pacific continued till spring season of 2019. Consequently most numerical models misread the season to remained below normal, with a hint of even possible drought. Accordingly, the monsoon had started on a disastrous note, suffering huge deficiency of 32% in the opening month of June. Statistical records never showed a possible ‘save’ in the later stages. However, the month of September turned an outlier to register a record surplus of 52%. This deluge was attributed to a large spike in the Indian Ocean Dipole (IOD), which registered An enormous rise of > 2°C towards fag end of the season.
The contrasting monsoon of 2018 & 2019 left important inferences for the subsequent seasons. An evolving El Nino need to be considered cautiously, as it has the potential to spoil the seasonal rainfall. Conversely, a strong IOD carries the ability to subjugate, an otherwise dwindling monsoon rains. The current monsoon season 2022 has also commenced under the shadow of -ve and growing IOD index. However, cooling of Pacific Ocean is promising continuation of La Nina conditions well in to the 2nd half of season. Therefore, monsoon 2022 is expected to ride over favorable La Nina, albeit battling adverse effects of -ve IOD.
