HYDERABAD: Raindrops may look all the same from the ground, but where they fall can influence how they are formed. A new study of Hyderabad has found that urbanisation can influence the development of rain clouds and the size of the raindrops they produce.
The study, led by researchers from the National Atmospheric Research Laboratory (NARL) and the Indian Institute of Science Education and Research (IISER), Tirupati, claims to be the first in India to examine how urbanisation affects the microphysics of rain — the processes through which tiny cloud droplets grow into raindrops — across different parts of Hyderabad.
To understand how the city influences rainfall, researchers studied rain over Hyderabad’s upwind, downtown and downwind regions and compared the observations with those from a nearby rural location. They found that rain-producing systems tended to develop deeper over the upwind and urban-core areas than over the downwind and rural regions.
That difference matters for a city that has expanded rapidly. Hyderabad’s urban area increased by 16.5% over the past two decades, while the city has also seen a rise in rainfall and losses linked to extreme weather. Its annual mean rainfall increased from 796 mm during 1971-1990 to 840 mm during 1991-2020.
The October 2020 deluge remains a stark reminder of what that vulnerability can look like. Hyderabad received 324 mm of rain on October 12 and 13, with more than 100 people reported killed and economic losses estimated at about USD 1.23 billion, according to the study.
So, what exactly is the city doing to the clouds? According to the researchers, the urban environment creates conditions that favour the development of deeper convective clouds.
Higher moisture, atmospheric convergence and other local weather conditions contribute to stronger vertical development of rain clouds over parts of Hyderabad. Storms rising beyond 10 km were found to occur about 2-3% more frequently over the upwind and downtown areas than over the downwind and rural regions.
But the story does not end with the clouds. The researchers also found differences in the distribution of raindrop sizes across Hyderabad’s urban landscape.
Urban growth doesn’t always mean more rain, warns study
The upwind and rural areas had large numbers of small raindrops. However, the upwind region also recorded a higher concentration of large drops, while the rural region had fewer large drops than the downtown and downwind areas. In the urban core, collisions among smaller droplets appeared to promote the formation of medium and larger raindrops.
The researchers arrived at these findings through an extensive field campaign using rain-monitoring instruments at four locations representing different parts of Hyderabad’s urban sprawl. ICRISAT was used as the upwind site, the India Meteorological Department’s Hyderabad centre as the downtown site, Anurag University at Aushapur as the downwind site and the National Remote Sensing Centre at Shadnagar as the rural reference site.
Rainfall observations collected from 2023 to 2025 were combined with satellite and atmospheric datasets to understand the differences across these locations.
The researchers, however, caution against a simple conclusion that urbanisation means “more rain”. Instead, the city alters the local atmosphere in complex ways, influencing rainfall intensity, timing, cloud development and raindrop formation. Urban heat, aerosols, changes in surface characteristics and turbulence can all interact with atmospheric conditions.
The findings could also have practical implications. The researchers said a better understanding of rainfall microphysics could help improve quantitative rainfall estimation using weather radars and the modelling of extreme weather events, with potential applications in mitigating hydrometeorological disasters.
They have also called for similar rain-microphysics studies across other Indian cities, noting that rainfall patterns can vary considerably from one urban environment to another.
The study was authored by Basivi Radhakrishna, Thota Narayana Rao and Roshan Kadbhane from NARL, and Kadiri Saikranthi from IISER-Tirupati.