At least 113 people have died across northern India after five days of heavy monsoon rainfall unleashed devastating flooding, as officials said the annual deluge was the greatest in 25 years.

Torrential rain began to fall across the states of Uttar Pradesh and Bihar on Thursday, submerging several major towns and cities. On Monday, officials in Uttar Pradesh said 93 people had died in three days from drowning, the collapse of homes and snake bites. 

Dozens of people were also killed in Bihar, where rescue workers used boats to reach residents trapped by waist-deep flooding in the state capital, Patna, home to some two million people. 

A major city hospital was inundated, with muddy waters filling wards in which patients still lay in beds. Authorities were also forced to evacuate 900 inmates from a prison in eastern Ballia district, police officer Santosh Verma said.

Deaths were also recorded in the states of Gujarat, Uttarakhand, Madhya Pradesh and Rajasthan.

Experts believe such extreme weather events are intensifying due to climate change, and that India will suffer heavier and more erratic rainfall with more frequent floods in the coming years.

The Indian Meteorological Society (IMS), a non-profit organisation, said that the ongoing deluge will ensure this September will be the wettest in over a century. 

The waters flooded a hospital in PatnaCredit:
Sachin Kumar/AFP

The Indian government’s Meteorological Department (IMD) said on Monday that monsoon rainfall was 10 per cent above average this year – its highest level for a quarter century. 

The monsoon – which accounts for around 75 per cent of annual rainfall – usually lasts between June and September, but this year is predicted to last until mid-October.

Its start was also delayed this year, with June rainfall 33 per cent below the long-term average, according to the IMS. This contributed to drought in the state of Maharashtra with 20,000 villages reporting a severe drinking water crisis.

Much of India was then lashed by excessive rainfall from July onwards, causing floods in several areas.

Over 160 people died in Kerala and Karnataka in August, with deaths also recorded in Odisha and Assam.

The Intergovernmental Panel on Climate Change predicts an annual increase in temperature in South Asia of 3.3°C by 2100. Studies say rising temperatures are creating a more moisture-laden monsoon system and higher levels of precipitation.

Many deaths in Uttar Pradesh were caused by house collapses, as well as drowning, lightning and snake bitesCredit:
Rajesh Kumar Singh/AP

The International Centre for Integrated Mountain Development predicts monsoon rainfall will increase by 25 per cent over the next 100 years.

“A study by the Council of Energy, Environment and Water (CEEW) shows in India mean precipitation is likely to increase in future,” said Dr Hem Dholakia, a senior research associate at CEEW. “Climate change will also make rainfall more erratic with longer dry spells and a higher risk of floods.”

Urban sprawl and poor city planning are thought to have worsened flooding.

“Deforestation, the absence of drainage systems and the flagrant violations of building norms in the entire state mean there has been a clear increase in water discharge,” said Anil Sood, the president of Spchetna, an NGO studying the effects of climate change in India.