Every year during the monsoon, we hear familiar flood stories of rivers overflowing, homes underwater, landslides, and families struggling to stay safe. But little is known about the flood patterns and the magnitude and intensity of floods that different regions in India experience and how they have been changing over time.
Riverine floods are not new to India. Last year alone, India experienced massive flooding in the states of Assam, Arunachal Pradesh, Sikkim, Manipur, Tripura, Uttar Pradesh, Himachal Pradesh, Kerala, Meghalaya and Gujarat. The floods and the subsequent landslides in the Wayanad district of Kerala, which was the worst hit, killed at least 373 people, injured over 200 and left 218 people missing.
However, a recent study finds that riverine floods are changing in magnitude and timing in interesting ways! To explore how riverine floods in India have evolved over the past 40 years, from 1970 to 2010, researchers Kuntla, S. K., Saharia, M., and Jain, S. K., from the Indian Institute of Technology (IIT) Delhi and the Indian Institute of Technology (IIT) Roorkee looked through records of river flows from 173 different monitoring stations spread across the country.
Floods are decreasing in some places, but not everywhere
The analysis reveals that monsoon flooding is decreasing across most of India, with this decreasing trend observed at as high as 74 percent of the gauging stations.
The central region of the Ganga basin shows a significant decrease in monsoon flooding by around 17 percent per decade. The Narmada basin too shows a consistent decreasing trend in the monsoon flooding, possibly due to the construction of dams in the region.
In the dry/arid Marathwada region of the Deccan plateau, which has been experiencing severe droughts in recent times, river flows are found to be decreasing at an average rate of 8 percent per decade during the monsoon season and 31 percent in pre-monsoon.
But this decrease is not to be found everywhere. The west-flowing rivers from Tadri to Kanyakumari (Chaliyar, Periyar, Bharathapuzha, Vamanapuram, etc.) in the Malabar coast interestingly show an increasing trend at an average rate of 8 percent per decade during pre-monsoon (March–May months) floods in the region.
The calendar is shifting: Floods come earlier or later
The timings of floods are also shifting. For example, the catchments covering the lower Yamuna basin located south-west of the Ganga show a shift towards an earlier calendar day, with floods occurring early due to early rainfall. In contrast, catchments in the upper Ganga experience late or delayed floods due to delays in rainfall. On an annual scale, catchments in the southern region of the country tend to experience floods later, whereas those in the central region have earlier flood occurrences.
What are the factors leading to regional changes in flood magnitude
Declining rainfall and soil moisture
The researchers find that the decrease in flood magnitude over central Ganga is associated with the decline in rainfall and soil moisture. This decline in the annual and monsoon rainfall is thought to be because of the warming of the Indian Ocean and the presence of atmospheric aerosols in the region.
Conversely, the increase in flood magnitude over the west-flowing rivers from the Tadri to the Kanyakumari basin on the Malabar coast of the country is because of the increasing magnitude of the pre-monsoon rainfall. Early rain leads to early pre-monsoon floods, and since rivers in the region do not receive any snow, all floods are rainfall-generated, and temperature does not seem to have any direct influence on floods.
A significant decrease in flood magnitude over arid climates during all seasons is seen, and that is observed to be due to climate change and various anthropogenic activities. Drylands are more sensitive to global warming and its impact, leading to increasingly arid conditions.
Smaller catchment areas can increase vulnerability to floods
A catchment is the area of land where rainfall collects and drains off into a common outlet—like a river, lake, or reservoir. Big catchments gather water from a wide region, while small ones respond more directly to local rainfall.
The researchers find that larger catchments are seeing floods getting smaller over time—possibly because they are better at absorbing and slowing down floodwaters, and climate or land-use changes might be reducing extreme events over large regions. At the same time, smaller catchments (under 1000 sq.km.) are seeing the opposite trend: floods are increasing. This is because these areas respond quickly to intense rainfall, do not have much room or natural systems to “store” floodwater (like wetlands or large riverbeds), and are thus prone to flash floods—sudden, dangerous floods after heavy rain.
The increasing flood trend in smaller catchments could mean higher risks for communities living nearby, especially with more frequent and intense rainstorms caused by climate change. Urbanisation (like replacing soil with pavement) can make this even worse.
Population and dam storage have a dampening effect on floods
More people using more water leaves less runoff to fuel floods. Large dams have a higher capacity to hold water, reducing peak flood magnitudes. These factors show the strongest negative correlation with rising floods in larger catchments.
Elevation affects how water arrives
The mean elevation of a catchment does not seem to directly impact how flood magnitudes are changing. So, a valley or mountain catchment does not impact stronger or weaker flood trends over time.
But elevation affects how water arrives. With global warming, snowfall zones are shifting to rainfall zones. More rain and less snow in high-altitude areas means earlier floods in spring/pre-monsoon. For India, snowfall may drop by 30–70 percent across major basins by 2070–2100. Regions like the Indus, Ganges, and Brahmaputra could see significantly earlier floods. Also, orographic effects (how mountains shape weather) cause highly localised climate-flood behaviour.
It’s time for India to rethink its approach to managing flood risks
Flood magnitudes are dropping across most of India, with the Ganga basin seeing a 17 percent decrease every decade. It also finds that the timing of floods is changing in different regions in India, indicating the complexity of flood dynamics in the country. If we do not understand and adjust to these changes, it could hurt the economy and environment, given that reservoir filling, ecosystems, and communities are adapted to the typical seasonal flooding patterns.
For example, smaller floods might not fill reservoirs enough, affecting water, farming, and power generation. In places like the Upper Ganga, early floods could cause big problems since emergency plans would need a complete overhaul. And on the Malabar coast, heavier pre-monsoon floods might damage crops during harvest time.
These findings can help us better understand how floods are changing in India and can guide improved ways to manage flood risks across different regions. To deal with these changes, we need a well-rounded approach—using better forecasts, smarter land planning, and climate-friendly water management—to reduce future damage, both in India and around the world.
Citation: Kuntla, S. K., Saharia, M., Jain, S. K. (2025). The changing magnitude and timing of riverine floods in India. npj Natural Hazards, 2 (44).