A Below-Normal September Ahead
The India Meteorological Department (IMD) has predicted that rainfall for September 2026 is most likely to be below normal across the country as a whole. This is defined as less than 91% of the Long Period Average (LPA), which for September is approximately
167.9 mm. The primary driver for this subdued forecast is the strengthening El Niño conditions over the Pacific Ocean, which are known to suppress monsoon rainfall in India. However, the forecast isn't uniform. While many parts of the country are expected to see a deficit, some areas in the northwest, northeast, and parts of southeast peninsular India might receive normal to above-normal rainfall. This regional variation is key to understanding the specific impact on different urban centres.
Why the Final Month is Critical
September is the withdrawal month for the monsoon, a gradual retreat that begins in the northwest around the first week and slowly moves southeast over several weeks. These final spells of rain are vital for topping up the reservoirs that supply drinking water to millions of urban residents throughout the long, dry months that follow. A poor performance in September can leave reservoirs with a significant deficit, placing immense stress on water management systems for the next nine to ten months. The season has already seen significant rainfall deficits, with overall storage in India's major reservoirs below the levels of the previous year as of late July. A dry end to the season could worsen this situation.
Mumbai: A Cautious Position
For Mumbai, a city entirely dependent on the seven lakes in its vicinity, the monsoon's performance is a direct measure of its water security. As of September 1, 2026, the collective water stock in these lakes stood at 95.87% of their total capacity. While this figure seems comfortable, it is slightly lower than the levels recorded at the same time in both 2025 and 2024. A below-normal September could prevent the lakes from reaching 100% capacity, which is the ideal buffer. While the IMD's short-term forecast up to September 8th predicts fairly widespread rainfall for the Konkan coast, which includes Mumbai, any subsequent weakness in the monsoon could leave the city with a smaller-than-desired water reserve for the coming year.
Chennai's Complicated Water Math
Chennai's primary rainfall comes from the Northeast monsoon (October-December), but the performance of the Southwest monsoon is crucial for replenishing regional reservoirs like Mettur and for groundwater recharge. The city is already facing a significant water supply deficit in 2026. The Mettur Dam, a key source for the delta region, was opened on September 1 with its water level at just over 91 feet against a full capacity of 120 feet, reflecting the strain from a weaker monsoon season. While the IMD forecast suggests a chance of normal to above-normal rain for parts of southeast peninsular India, which could offer some relief, the overall subdued national picture is a concern. The city administration is already undertaking extensive desilting of drains in preparation for its main monsoon season, highlighting the constant battle against both flooding and water scarcity.
Bengaluru and Delhi: Groundwater and River Woes
Bengaluru's water crisis is a chronic issue, stemming from depleting groundwater and the strain on the Cauvery river. The city has struggled with a weak monsoon, and a dry September would only intensify the pressure on its already stressed aquifers. Much of Bengaluru's water security now depends on capturing rainwater to recharge groundwater, a practice that becomes less effective with reduced rainfall. For Delhi, the situation is different. Its water supply depends on rivers like the Yamuna and the Beas, which are fed by monsoon runoff in the northern plains and the Himalayas. The IMD forecast of potentially normal to above-normal rain in parts of Northwest India could be a positive sign for river flows supplying the capital. However, a low-pressure area active over Central India in early September is expected to bring heavy rainfall to Uttar Pradesh and Madhya Pradesh, which could influence river levels downstream.
