Here's what makes 2023 monsoon different from previous ones

Headline numbers suggest that the 2023’s monsoon is average and nothing out of the ordinary. India has received 315.2 mm of rain from June 1 (the average start date) to July 16, according to the gridded dataset of the India Meteorological Department (IMD). For this part of the monsoon (the average end date is September 30), this is the 55th-highest quantity of rain received in the past 123 years for which this data is available — a number recorded roughly in the middle of all the monsoon seasons. It comes closest to the 1961-2010 average of 302 mm. However, a more granular analysis suggests that this monsoon has many peculiarities that make it unique: delay in onset, intensity of rain, and its geographical patterns.To be sure, the overall rainfall quantum that may be normal for the season does not reflect the extremes in a season in terms of impact, distribution and scale of rainfall. For example, till July 18, India recorded zero percent deficiency with 43% excess over northwest India; 19% deficiency over east and northeast India; 23% deficiency over peninsular India and 4% excess over central India.Of 36 meteorological subdivisions, 13 are in the deficient category (-59% to -20%); 12 are normal (-19% to 19%); five are in excess (20% to 59%) and six are in large excess (60% or more). This year, the monsoon made an onset over Kerala on June 8, but conditions were initially weak for two weeks because of extremely severe cyclone Biparjoy.June had ended with a 10% monsoon deficiency. But by the end of June, the monsoon started sprinting. On June 23, the northern limit of monsoon (NLM) or the monsoon line had only covered the peninsula and part of east India, but in two days it covered nearly the entire country leaving only parts of Gujarat, Rajasthan, Punjab, which experts said was unusual because monsoon onset was delayed but it covered the country earlier than the normal date. In July, the Arabian Sea branch of the monsoon became active bringing heavy rainfall to the west coast, including Maharashtra and Konkan region during the first week and thereafter an interaction between a western disturbance and the monsoon winds caused extreme record rainfall over parts of Himachal Pradesh, Uttarakhand, Punjab, Haryana and Delhi.Himachal Pradesh and Uttarakhand faced landslides, mudslides, and massive damage to bridges, highways and other infrastructure while in Delhi, Yamuna breached the 45-year flood level inundating several parts of the city and displacing thousands of people. Interestingly, the IMD had forecast that below-normal rainfall was likely over many areas of northwest, northeast and southeast peninsular India in July. On Sunday, a low-pressure area formed over north Odisha and adjoining Gangetic West Bengal and Jharkhand which is expected to bring heavy and widespread rainfall over central and adjoining east India in the next five days. Rainfall will increase over the west coast. Monsoon will be active for a week according to IMD, but will that mean erratic extremely heavy, record rainfall again for some regions?“This trend is well known. Studies made in 2006 and 2008 based on IMD gridded data (developed by my team and I) clearly showed that the frequency of heavy rainfall events is increasing and the frequency of light to moderate rain is decreasing. Subsequently, there have been many studies suggesting the same conclusion. We attribute this mostly to global warming even though there could be a small influence on natural variability. In the future scenario, climate models suggest this trend will go on. It is very alarming. Heavy rains contribute most of the seasonal total. This is valid whether the monsoon is bad or good. I have pointed out this phenomenon again and again. We need to prepare for it,” said M Rajeevan, former secretary, ministry of earth sciences and climate scientist.“Overall monsoon rainfall may be in the normal category but its impact and scale is far from normal. There's a clear climate shift in monsoon patterns. We are seeing long deficit rainfall periods and short spells of heavy rains in a few days. Some regions are getting a month's rainfall in a day or a few days' time. This is because due to global warming, there's more moisture available, and since the moisture-holding capacity of air increases with temperature, there's more water for a heavy downpour,” said Roxy Mathew Koll, climate scientist, the India Institute of Tropical Meteorology.“Due to global warming, there's more moisture available, and since the moisture-holding capacity of air increases with temperature, there's more water for a heavy downpour,” he added.But there are other elements to this year’s monsoon that are not only unique, but also pose cause for concern.One of the most delayed monsoon onsetsThe official monsoon season begins on June 1 because this is the normal date for the arrival of the monsoon system on the Kerala coast. This year, the system arrived at the Kerala coast only on June 8, seven days later than usual. Monsoon onset dates over Kerala based on the objective criteria in use currently are available from 1971 onwards. This shows that the delay this year is rare. There have been only 10 years since 1971 (apart from 2023) when the monsoon has arrived on or after June 8. To be sure, despite the delayed onset – partly a result of Cyclone Biparjoy -- the monsoon covered most of north-western India earlier than it usually does.Heavier intensity rain ranks higher than overall rainThat 2023 is ranked in the middle of all monsoon seasons for overall monsoon rain, despite being unusually late suggests that it has rained faster this year. This can also be verified. The average rain for the 1961-2010 period shows that 46% of the rain from June to July 16 took place in July. This year 51% of the rain so far has taken place in July. This is also reflected in the intensity of rain. If it rains more than 35.5 mm in a day at a place, the IMD classifies that rain as different kinds of “heavy” and “extreme” rain. HT analysis of IMD gridded data shows that such rain is ranked 33rd highest this year since 1901, although overall rain (of all intensities, taken together) is ranked only 55th highest. This suggests that such heavy-intensity rain has been more than usual this year.How much more than usual is such rain this year? 12% compared to the 1961-2010 average, the benchmark for rain. In comparison, “light” rain (up to 7.5 mm in a day) is 4% less than the 1961-2010 average making it ranked 44th lowest, while “moderate rain (7.5 mm to 35.5 mm in a day) is 1% less than the benchmark and the 55th lowest.Rain is unusual for three-fourths of the countryIt is not just the delay in onset and the intensity of rain that is unusual this monsoon. Its geographical patterns are also unusual. Close to three-fourths of the country's area (73%) has received either too little or too much rain. Only 27% of the country by area has received rain with a surplus or deficit of less than 20% than the 1961-2010 average, a benchmark the IMD uses for calling rain "normal" at the local level. 38% of the country has a deficit of 20% or more, with 6% of India having an acute deficit of 60% or more. Similarly, 36% of India has received a surplus of 20% or more, with 21% having a large surplus of 60% or more. Number of days of rain unusual for a fourth of the countryApart from the amount of rain, the number of days it has rained is also unusual for around one-fourth of the country. To be sure, there is no official metric for measuring how unusual the frequency of rain is, like the 20% or higher deviation that the IMD uses as a benchmark for the amount of rain. HT has considered an increase or decrease in days of rain by seven days as a benchmark for this analysis, and found that while 72% of the country fulfilled this benchmark in the 46 days of monsoon up to July 16, in 9% of the country’s area, it rained for a week or fewer days than it rained on average during the 1961-2010 period. In 18.9% of the country’s area, it has rained for a week or longer than it did on average during the 1961-2010 period.“There was heavy rainfall over north India even before the monsoon set in due to various weather systems. That had affected vegetables. Now in July, a rare interaction between a western disturbance and the monsoon trough caused intense rainfall, landslides and floods which impacted vegetables and fruits that cannot withstand heavy rain. On the other hand, the sowing of crops was delayed in central and east India because of delayed monsoon rainfall. The skewed distribution will have an impact on the availability of food and food prices this monsoon,” said Mahesh Palawat, vice president, climate and meteorology, Skymet Weather.

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