It is possible to be killed by floods in Mumbai, but not really to be surprised by them. On 29 August, the city was battered by a monsoon storm which left homes, highways and hospital floors submerged, and shut down the commuter railway which has to carry more people every day than live in Denmark. More than 20 people are dead: swept away or crushed as multi-storey buildings collapsed. Bodies are still washing ashore.

Instead of feeling surprise, though, Mumbai treated the deluge like an unwelcome guest who keeps coming by and trashing the place. The most unnerving collective flashback was to 26 July 2005. Ferocious rainfall that day turned the city into a lethal aquatic obstacle course, which 700 people did not survive. That year’s flood, like this one, was followed by a flood of assurances from elected leaders, and civic pledges to protect waterways and mangroves, and renewed attention to how a metropolis built largely on tidal estuary and marine “reclamations” could so easily return to the water.

The storm in Mumbai deposited 15% of the city’s annual rainfall in a single day

As Mumbai wades through deja vu, provinces further east are struggling to keep their heads above water, as they have been for weeks. Hundreds of villages have been abandoned in Bihar, West Bengal and Assam. The direct death toll may exceed 800 (no one is likely to count the lives lost or stunted in the longer term – the result of crops, homes and public works swept away in some of India’s poorest states).

Like Mumbai, though, these are places accustomed to flooding. Some of the world’s largest rivers flow through them, and spill their banks each monsoon. The mutability of land and water is an essential trait of parts of Bengal and Assam, and a theme in their literature. Amitav Ghosh, the bard of this theme in the English language, wrote of Bengal’s mangrove forests: “Here, in the tide country, transformation is the rule of life: rivers stray from week to week, and islands are made and unmade in days.” So are the plains, on occasion.

Flood-affected villagers in Morigaon district, east of Gauhati, Assam. Photograph: Anupam Nath/AP

Floods in eastern India are often woven into tradition, as part of the cycle that rejuvenates fields, fish stocks and wetland forest. This inclines Indians to acceptance. “Don’t try to fight nature,” the actor Amitabh Bachchan tweeted on the night of 29 August, as the storm abated in Mumbai. “Don’t put blame.” Well, we do put blame, and object to state incompetence, reckless urbanisation and failures of disaster response. Afterwards, though, especially when watching from indoors, we cherish the monsoon’s show of strength and surplus, and feel the familiarity of the flood. This is a deadly mistake.

In Mumbai and Assam, recent floods have occurred where flooding is traditional, but no longer for traditional reasons. The storm in Mumbai deposited 15% of the city’s annual rainfall in a single day. The same occurred on 21 August in Chandigarh, northern India. Bengaluru, in the south, received 30% of its annual average on 15 August – the heaviest rainfall recorded in the past century.

Mumbai’s storm is classed as an “extreme rain event”. Climate change models predict that they will become more frequent and proliferate into parts of India never thought of as monsoon hotspots, where the pumps are even less likely to be primed. This is the new, turbulent nature of our monsoon: that we are receiving more and more of our rainfall in extreme doses (which causes floods), and less in between the major deluges, which is when fields are fed and water tables recharged. For India, more flooding and more drought are not two possible futures. Both are here together, already.

The submergence of so much of India by this monsoon is not an expression of timeless natural rhythms or even classic state failures. Extreme rain events mean that, as environmental scientist Sunita Narain put it, “floods in the time of drought are India’s new normal”. Recognising this is integral to creating homes, farms and infrastructure which can survive the changing monsoon.

The government of Narendra Modi was elected, in part, on a promise of economic development, which it has struggled to deliver. One way to defend our gains, in real terms, is by moving fast to help cities and districts adapt: both to control flooding and save lives, and to harvest heavy rainfall and save water.

• Raghu Karnad is journalist and editor-at-large at The Wire