Chennai, October 5: Accounting for atmospheric aerosols in weather and flood models could improve the simulation of extreme rainfall and urban flooding, according to an international study led by the Indian Institute of Technology Madras (IIT Madras).
The study, which examined Chennai’s extreme rainfall and flooding in December 2015, found that explicitly representing aerosol–cloud interactions improved simulated rainfall over the Adyar basin by about 22% compared with a control simulation. The improvement was carried through the modelling chain, resulting in an approximately 50% improvement in the accuracy of simulated flood inundation, according to the researchers.
Atmospheric aerosols are tiny particles suspended in the air that can influence cloud formation and rainfall. The researchers examined how variations in aerosol conditions and cloud condensation nuclei (CCN)—particles around which cloud droplets form—affect rainfall and, consequently, runoff, reservoir inflows and flood inundation.
The research involved IIT Madras, the GFZ Helmholtz Centre for Geosciences in Germany, the Japan Aerospace Exploration Agency (JAXA) and Kathmandu University, Nepal. The collaboration combined atmospheric science, hydrology, hydraulic modelling and Earth observation.
The findings were published in Natural Hazards and Earth System Sciences, a peer-reviewed international journal.
The researchers used the Weather Research and Forecasting (WRF) model to simulate atmospheric processes during the 2015 Chennai event under different aerosol conditions. The resulting rainfall fields were then used in HEC-HMS for hydrological modelling and HEC-RAS for hydraulic and flood-inundation modelling over the Adyar basin.
Dr Chandan Sarangi of the Department of Civil Engineering, IIT Madras, and corresponding author of the study, said conventional urban flood forecasting often treats rainfall primarily as an input to runoff models, while the atmospheric processes that influence the spatial and temporal distribution of rainfall may not be fully represented.
“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,” Sarangi said.
Prof S. N. Kuiry of the Department of Civil Engineering, IIT Madras, said rainfall forecasting for a megacity such as Chennai also has implications for water-resources management because the timing and spatial distribution of extreme rainfall can influence runoff, reservoir inflows and flood forecasting.
The study could have implications for reservoir management and urban flood preparedness in Chennai, particularly during extreme rainfall events when decisions on reservoir storage and releases are time-sensitive, the researchers said.
The researchers, however, cautioned that the framework is not yet an operational flood-forecasting system. They said further studies are required to determine whether the improvements observed during the 2015 Chennai event can be reproduced consistently across other extreme rainfall events and in other cities.
They also identified the need for better high-resolution observations of atmospheric aerosols, CCN and urban emissions to improve model representation and validation. Reducing the computational demands of such high-resolution simulations would also be necessary for their potential use in operational forecasting.
The study was supported by the Asia-Pacific Network for Global Change Research (APN).
The researchers said the modelling framework could eventually be tested in other rainfall-prone megacities where rapid urbanisation, intense precipitation and limited water-storage capacity create complex flood-management challenges.
The study was co-authored by Dr N. Nithila Devi of IIT Madras and GFZ Helmholtz Centre for Geosciences; Dr Rakesh Teja Konduru of JAXA; Dr Kundan Lal Shrestha of Kathmandu University; Oscar Paul, Prof Soumendra Nath Kuiry and Prof Chandan Sarangi of IIT Madras.
Comments are closed.