Rain check: How the monsoons went from 33% deficient to 10% higher than normal, all in three months

In a normal year, the monsoon begins to withdraw from the Indian subcontinent on September 1. But this year, the withdrawal is likely to start on October 10, more than a month late, according to Indian meteorological department.

Even though the department predicted a near-normal monsoon back in April, the entire season has been remarkable in its unpredictability. First, the monsoon winds arrived one week late in Kerala, slowing down further as they travelled up the peninsula, reaching Mumbai three weeks later.

The delayed onset of the monsoons initially meant a rainfall deficit of 33% in June. But the season is ending with 10% higher rainfall than the long term average.

This is largely because of concentrated bursts of heavy rain in short periods of time, say scientists. The extreme precipitation has caused destructive floods in as many as eight states. At the start of August, 80 people died in Karnataka. Nearly the same number perished in Bihar towards its end of September.

‘A special feature’

The average rainfall recorded for the months of June-September, taken over 50 years from 1951-2000, comes to 88 cm of rain. This year, the country as a whole received 97 cm of rain. This is 110% of the long period average.

The cumulative rainfall departure from normal – which is how much the rain departed from the long period average for June 1 to that week – shows the deficit was very high in the first three weeks of the season.

It then made up very quickly to normal and above-normal in most districts by its seventeenth week.

DS Pai, a scientist at Indian meteorological department in Pune, said that rainfall received in this year’s monsoon season was a “special feature” that is not likely to repeat next year.

This year’s rainfall would fall under the category of “above normal”, he said. In June and July, the rainfall deviation from the long term average was 82%. By the second half of the monsoon season, in the months of August and September, this had jumped to 110%.

“We predicted ‘normal’ but we got 10% more rain of what was predicted,” Pai said. This happened because of a greater intensity of low pressure systems that cause the air to rise and form clouds, leading to precipitation, he explained.

Asked why the Indian meteorological department’s prediction was inaccurate, Pai claimed heavy spells of rainfall can only be predicted few days before they occur, not “four months in advance.”

Regional variations

Central and South India received the most rain, in contrast to last year, when both areas ran a deficit. Parts of the country’s North West and North East still received deficient rainfall, especially Delhi, Haryana and Western Uttar Pradesh. This was especially worrisome in the North East, because the region also ran a 24% deficit last year.

Impact of an unpredictable monsoon

The delay in the monsoon this year led to delayed sowing of kharif or summer crops. Then, destructive rains in several regions caused extensive damage of crops.

Still, the cumulatively above-average rainfall means that reservoirs are full, some groundwater has been replenished and that farmers sowing for the rabi or winter season will have the water they need for a bumper crop.

Also read: How reservoirs in India went from dry to overflowing all in two weeks