IIT Madras study reveals air pollution could help improve rainfall, urban floods forecasting

The Indian Institute of Technology Madras (IIT Madras) conducted an international study and found that atmospheric air pollution could have an important role in improving the forecasting of rainfall and floods.

The engineering institute-led study revealed that explicitly accounting for atmospheric aerosols, tiny particles suspended in the air that can influence cloud formation and rainfall, can substantially improve simulations of extreme rainfall and the resulting urban flooding.

Explaining the importance of the research, Chandan Sarangi, department of civil engineering, IIT Madras, said: “Urban flood forecasting is often treated primarily as a rainfall-to-runoff problem. The problem in urban flood forecasting is that rainfall spatial and time distribution is not well captured by our weather models. What happens in the atmosphere before and during rainfall can significantly influence the spatial rainfall pattern. By explicitly representing aerosol–cloud interactions, we can better capture the spatial and temporal characteristics of extreme rainfall within urban regions and consequently improve flood inundation simulations”

The IIT Madras’s study used the Weather Research and Forecasting (WRF) model to simulate the atmospheric processes associated with the 2015 Chennai event under different aerosol conditions.

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IIT Madras's study on atmospheric science, hydrology

The resulting rainfall fields were then coupled with HEC-HMS for hydrological modelling and HEC-RAS for hydraulic and flood-inundation modelling over the Adyar basin, the official statement read.

The results showed that explicitly representing aerosols led to an approximately 22% improvement in simulated rainfall over the Adyar basin compared with the control simulation.

This improvement propagated through the modelling chain, resulting in an approximately 50% improvement in the accuracy of simulated flood inundation compared with the control case, it added.

The research was carried out through a multidisciplinary collaboration between IIT Madras, GFZ Helmholtz Centre for Geosciences, Germany, Japan Aerospace Exploration Agency (JAXA), and Kathmandu University, bringing together expertise in atmospheric science, hydrology, hydraulic modelling and Earth observation.

The researchers used Chennai’s December 2015 extreme rains and flooding event as a case study. By incorporating aerosols and cloud condensation nuclei (CCN), particles around which cloud droplets form, into high-resolution atmospheric simulations, they investigated how changes in atmospheric aerosol conditions affect rainfall and, subsequently, runoff, reservoir inflows and flood inundation.

The findings were published in Natural Hazards and Earth System Sciences, a peer-reviewed, open-access international journal covering research on natural hazards, their impacts on society, environment, processes and interactions within the Earth system that drive hazard risk.