Weather Bee: Why India has a heavy rain deficit despite rain-related disasters

Flash floods have been reported from hilly regions in India’s north this month. While the loss of lives due to rains has been relatively small in metros such as Delhi and Mumbai, and often resulted from electrocution, building collapse, or infrastructure failure, these cities have also seen rain-related deaths this month. This might lead one to believe that the rains in the 2025 monsoon season – the season runs officially from June to September – are extreme. This is the case for the regions where disasters have struck, but the overall amount of intense rainfall in the country or the expanse of such rainfall is not, an HT analysis shows. Here's how.Country-level trends in the amount of intense rain can be assessed by tracking the average of “rather heavy” or higher-intensity rain (hereafter referred to as heavy rain) in the country.India Meteorological Department (IMD) defines heavy rain as rainfall of more than 35.5 mm at a place in 24 hours, the highest frequency at which it provides gridded data for rain.By adding up heavy rain at all places that received such rain, and then averaging the amount over the country’s entire area, one can obtain an area-averaged amount of heavy rain for the country, which combines both the amount and expanse of heavy rain in one number.The average heavy rain in the 2025 monsoon season for India is 258.7 mm. This is the 36th lowest amount of heavy rain since 1901, the earliest year for which IMD has published gridded data. It is also 7.2% less than the 1971-2020 average for heavy rain. IMD considers the 1971-2020 average as the Long Period Average (LPA) for tracking rainfall performance.To be sure, while the 36th lowest rank is low, the 7.2% deviation is within one standard deviation of heavy rain in the 1971-2020 period, which is 11%. This suggests that while there is a deficit in heavy rain this year, and a few years might have recorded such a deficit, a deviation of 7.2% from the LPA is not abnormal. However, as trends in lower intensities of rain show, heavy intensity rain is indeed a drag on the monsoon’s overall performance this year. Both light and moderate intensity rainfall have a surplus in this monsoon season. Is it the case that there is a deficit in heavy rain overall in the season, but not in August, when disasters often appear to have struck? Not really. Both July and August – two rainiest months of the monsoon season – have a deficit in heavy rain. It is the relatively drier month of June that had a surplus in heavy rain. If the deficit in heavy rain in 2025, including in August, appears counter-intuitive to the news of disasters, it can be visually understood by comparing this year’s monsoon with 2024’s. The 2024 monsoon had received 310 mm of heavy rain up to August 22, ranked 17th highest since 1901; and its contrast with the 2025 monsoon highlights one reason why heavy rain has a deficit at the country level this year. Heavy intensity rain has a surplus in parts of Himachal Pradesh, Uttarakhand, Jammu and Kashmir, as well as Delhi and Mumbai in both years, places most vulnerable to disasters when rain is intense. The shift from surplus heavy rain to no heavy rain has happened in other places, like the extreme western parts of Rajasthan and Gujarat, which are less densely populated and, therefore, less vulnerable to a disaster. As the maps suggest, the expanse of heavy rain decreasing is one reason why there is a deficit in such rain at the country level. Numbers make this even clearer. 38% of the country had a surplus of 20% or more in heavy rain last monsoon compared to 32% of the country this monsoon. Similarly, 17% of the country has received no heavy rain this monsoon compared to 15% last year.Clearly, heavy rain at some places is no guarantee of a surplus at the country level. This analysis also highlights that disaster frequency need not be correlated with the country-level average of heavy rain. This is because disasters are a combination of intense rain and a place’s ability to cope with it. Heavy rain in uninhabited or sparsely populated land has less chance of resulting in disasters.