Weather Bee | As monsoon season nears end, skew in rainfall persists across India

At the country level, India has received 853.7 mm of rain so far this monsoon, according to the gridded data of the India Meteorological Department (IMD). This is the 11th highest rain for the June 1-September 11 period since 1901, the earliest year for which IMD has published gridded data. It is also 12% more than the 1971-2020 average (considered the Long Period Average or LPA for measuring rain’s performance) for this part of the season.

The above statistics mean that there is little doubt that this is a very rainy monsoon season so far. In fact, it is also likely to end up in a very rainy season. For example, the 853.7 mm of rain India has received so far is just 3.3 mm short of the LPA for the entire June-September period. The rains in the remaining 19 days of the season can easily surpass that 3.3 mm shortfall, as IMD’s extended range forecast shows most of India receiving some rain every week up to the week ending October 3.

Although a surplus is likely for the season overall, not all parts of the season have been equally rainy. For example, while June had a 7% deficit compared to the LPA, the departure in July, August, and September so far is a surplus of 15%, 18%, and 23% respectively. This, however, must not be taken to mean that September is responsible for most of the season’s surplus. As the accompanying chart shows, the departure in September in absolute terms is not as much as it was in August or July.

Similar to the skew seen in individual months, there is a skew in the geographical distribution of rain. Only 35.6% of the country has received rain within 19% of the LPA that the IMD classifies as “normal”. On the other hand, 20.9% of the country has a deficit of 20% or more, which is classified as “deficient”; and 43.5% of the country has a surplus of 20% or more, which is classified as “excess”.

To be sure, the geographical skew has seen one kind of improvement over the course of the season. The deficient area has decreased over time. Such area was 33.2% on July 31 (the middle of the season) but is now only 20.9%. However, this improvement has not increased the area under normal rain much, as some regions with normal or deficient rains up to July 31 have a big surplus now. The 12.3 percentage points decrease in the deficient area has increased the normal area by just 2.7 percentage points but increased the area under excess rain by 9.6 percentage points. The latter kind of change has happened largely because of Gujarat and Rajasthan, which were flooded due to cyclone-like weather systems in the past few weeks.

The most worrying aspect of the geographical skew is, however, not that 21% of India is still deficient. Like all averages, the average rainfall for India always hides regional variations. The worrying aspect of the deficient area is its concentration in the Indo-Gangetic plains, a trend also seen mid-season. These plains have been drying up long-term in the monsoon season, with the 2024 season extending that trend further. As HT explained earlier, this can create future economic distress in this region, as it is more dependent on agriculture than the rest of the country.

Abhishek Jha, HT’s assistant editor-data, analyses one big weather trend in the context of the ongoing climate crisis every week, using weather data from ground and satellite observations spanning decades.