Under new benchmark, Delhi sees 4.6mm drop in annual rain

August, Delhi’s wettest month, now has a monthly rainfall average of 233.1mm -- a drop of 14.6mm from the previous normal of 247.7mm.

The decision by the India Meteorological Department (IMD) to revise its long-period average (LPA) for monthly rainfall for all states and Union territories from the earlier benchmark of 1960-2010 to that of the 1970-2020 period has resulted in Delhi seeing a 4.6mm drop in its normal annual rainfall mark.

IMD data shows that Delhi received 34.8mm of rainfall in June 2021, a deficit of 47% as compared to the normal of 65.5mm. This year, the city received 24.5mm rain in June, a deficit of 67% as compared to the new normal of 74.1mm. (ANI)

Met officials say the new LPA came into effect from June, and Delhi’s normal annual rainfall as per the revised LPA now stands at 774.4mm, compared to the 779mm earlier.

“Overall, there is a reduction in the annual rainfall mark by 4.6mm and Delhi is expected to receive 774.4mm as compared to 779mm until last year. Based on this figure, we compare whether Delhi received above average rainfall or below average,” a Met official said, on condition of anonymity.

These figures all pertain to rainfall Delhi receives at the Safdarjung observatory, which is considered representational of Delhi’s weather, both in terms of temperature and rainfall.

The change in the normal benchmarks for each month has also resulted in an increase in the city’s average rainfall for five of the first six months, most notably in May, which now has a monthly rainfall average of 30.7mm as compared to 19.7mm until last year. In comparison, most months in the second half of the year have seen a reduction in the monthly normal mark, including the monsoon months of July, August and September. August, Delhi’s wettest month, now has a monthly rainfall average of 233.1mm -- a drop of 14.6mm from the previous normal of 247.7mm.

In August 2021, Delhi received 214.5mm of rainfall, a 13% deficit as compared to the previous normal of 247.7mm. This year, the city received just 41.6mm of rainfall in August – a deficit of 82% as compared to the revised normal of 233.1mm, the data shows. (HT Illustration)

The Met official quoted above said that for a significant increase or decrease in the normal to take place, there has to be a significant change in the rainfall Delhi received between 1960-1970 and the last decade.

“If there is a decrease in the normal, for instance in August, which has now reduced by nearly 15mm, it means Delhi did not receive enough rain over the last one decade as compared to what it had in the 1960-1970 period and that has impacted the overall average. It is also significant as August is the wettest month for Delhi in terms of rainfall and a reduction of 15mm is again not a small amount,” the official said.

IMD data shows that Delhi received 34.8mm of rainfall in June 2021, a deficit of 47% as compared to the normal of 65.5mm. This year, the city received 24.5mm rain in June, a deficit of 67% as compared to the new normal of 74.1mm.

Similarly, Delhi in July 2021 received 507.1mm of rain compared to a normal of 210.6mm -- an excess of 141%, while this year, Delhi in June received 286.3mm of rain, an excess of 37% as compared to the new normal of 209.7mm.

In August 2021, Delhi received 214.5mm of rainfall, a 13% deficit as compared to the previous normal of 247.7mm. This year, the city received just 41.6mm of rainfall in August – a deficit of 82% as compared to the revised normal of 233.1mm, the data shows.