Ecostani | Monsoon pattern changing with Himalayas, west coast recording more extreme rain
Unless India has a plan to build climate-resilient urban infrastructure, the flooding of cities will become more intense in the future
This year’s monsoon has again shown that the intensity of extreme weather events is rising, leading to an increase in excessive flooding and damage to infrastructure apart from human loss.
The 2024 monsoon is one of the wettest recorded in India’s history with 927 mm of rainfall recorded as against normal of 861 mm, a positive departure of 7.7%, until September 28. While the number of deaths has not been high because of timely intervention by relief agencies, the impact on physical infrastructure has been huge with states seeking relief worth thousands of crores of rupees from the National Disaster Relief Fund (NDRF).
Rainfall data analysis by the Indian Institute of Technology, Gandhinagar (IIT-G), however, showed a localised increase in extreme rainfall, indicating that unusually heavy rainfall was occurring and impacting some places more than others. Even though an area’s annual total rainfall may remain within expected levels, it could see more concentrated and extreme rainfalls over shorter periods, leading to flash floods and overwhelming drainage systems.
“We are observing shifts in weather patterns and extremes that challenge the assumptions based on historical data,” said Udit Bhatia, who leads the Machine Intelligence and Resilience (MIR) Laboratory at IIT Gandhinagar, adding that relying too much on historical rain patterns might no longer be the safest approach. Infrastructure designed using outdated data may not be fully equipped to handle the intensity of future extremes, he said.
The lab has developed the Precipitation Extremity Volatility Index (PEVI) which measures the ratio between the magnitudes of return periods and provides a clearer picture of where additional investment in infrastructure resilience is needed. It identifies areas more vulnerable to extreme rainfall based on historical rainfall data.
Nationally, the analysis said, the trends in PEVI from 1901-1960 to 1961-2023 suggest a nationwide increase in vulnerability to extreme precipitation events. The median PEVI value for India has risen from 1.27 to 1.31, reflecting a growing risk of extreme weather events across the country, according to the study. Coastal regions, especially in Gujarat and Kerala, have seen the largest increases in PEVI, with significant rises in both the frequency and intensity of extreme rainfall.
In Kerala, an increase in extreme precipitation events over time is more profound in the central and southern regions of the state. Up to a 30% increase in PEVI values has been observed across multiple districts including Wayanad and Kozhikode. The IIT identified areas in parts of Idukki, Kottayam, and Pathanamthitta districts as hotspots for increased precipitation volatility.
In the 1901-1960 period, Kozhikode showed mostly low to moderate PEVI values (light blue to green), ranging approximately from 1.20 to 1.30, which increased to 1.40 in the period 1961-2023. Similarly, PEVI in Wayanad increased to 1.35, in some places even to 1.45, indicating high extreme rainfall vulnerability.
In Gujarat, an analysis of PEVI across two periods—1901-1960 and 1961-2023—showed that there was a sharp increase in the index in coastal areas such as Kachchh, Devbhumi Dwarka, Jamnagar, and Porbandar. In contrast, inland areas like Vadodara and Bharuch show decreased PEVI values, indicating that flooding in these regions may be more a consequence of poor urban planning and drainage infrastructure than extreme rainfall events.
The northern plains, covering states like Rajasthan and Uttar Pradesh, exhibit positive changes in PEVI values, particularly in many districts where increases of 10-30% have been observed. In contrast, regions such as Haryana, Punjab, and Delhi show mixed signals, reflecting varied patterns of weather extremes. This variability suggests that local factors, including land use changes, irrigation practices, and urbanisation, could be driving these mixed results.
Similarly, Maharashtra—both its coastal and inland regions—has seen a significant increase in PEVI values, with changes of up to 35%. This indicates a growing intensity of extreme weather events across the state, presenting new challenges for its infrastructure systems. Coastal Maharashtra, in particular, has become increasingly vulnerable to extreme rainfall, exacerbating the risk of urban flooding, especially in densely populated cities like Mumbai, the analysis said.
Among the Himalayan states, the PEVI value has increased by 24-32% all across from Himachal Pradesh to northeastern states. In recent years, extreme rainfall events have occurred in Himachal Pradesh, Uttarakhand and Sikkim causing huge loss of life and damage to hydel projects such as Rishi Ganga in Uttarakhand and Teesta IV and V in Sikkim in 2023 and 2024 respectively.
However, the eastern states have witnessed low PEVI values showing minimal changes in rainfall patterns even though parts of northern Bihar have witnessed frequent floods of heavy rainfall in the catchment area of the Kosi river originating from Nepal.
The Indo-Gangetic Plain, stretching from Punjab to West Bengal, shows a mixed pattern of change. While some areas (e.g., parts of Uttar Pradesh and Bihar) show slight decreases in PEVI, others (e.g., parts of Punjab and Haryana) show moderate increases. “This heterogeneity suggests localized factors may be influencing precipitation patterns in this densely populated and agriculturally important region,” the analysis said.
The analysis also highlights the increasing vulnerability of urban areas to extreme rainfall as the infrastructure is not built to cope with sudden increases in rainfall. During this monsoon, people in Delhi, Mumbai, Surat, Jaipur, Chandigarh, Gurugram and Bengaluru saw massive flooding.
Unless India has a plan to build climate-resilient urban infrastructure, the flooding of cities will become more intense in the future as the intensity of extreme rains increases. There is enough science available on building climate-resilient infrastructure: India needs to invest in it to improve life in cities where half of the country’s population will live by 2050.
Chetan Chauhan, national affairs editor, analyses the most important environment and political story in the country this week
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