Air pollution could improve urban flood forecasting: IIT Madras study
Chennai, Oct 5 (TNT): Atmospheric air pollution could play a key role in improving rainfall forecasts and urban flood simulations, according to an international study led by the Indian Institute of Technology Madras (IIT Madras).
The study found that explicitly accounting for atmospheric aerosols, tiny particles suspended in the air that influence cloud formation and rainfall, could substantially improve simulations of extreme rainfall and resulting urban flooding.
The study was conducted by researchers from IIT Madras, GFZ Helmholtz Centre for Geosciences, Germany, Japan Aerospace Exploration Agency (JAXA) and Kathmandu University, Nepal, the Institute said in a release on Monday.
The researchers used Chennai’s December 2015 extreme rainfall and flooding event as a case study and incorporated aerosols and cloud condensation nuclei (CCN) into high-resolution atmospheric simulations to examine their impact on rainfall, runoff, reservoir inflows and flood inundation.
The findings were published in the peer-reviewed journal Natural Hazards and Earth System Sciences.
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 data were coupled with HEC-HMS for hydrological modelling and HEC-RAS for hydraulic and flood-inundation modelling over the Adyar basin.
The study found that explicitly representing aerosols resulted in an approximately 22 per cent improvement in simulated rainfall over the Adyar basin compared with the control simulation.
The improvement subsequently led to an approximately 50 per cent improvement in the accuracy of simulated flood inundation.
IIT Madras Department of Civil Engineering Professor and corresponding author Chandan Sarangi said rainfall forecasting for urban flood management needed to account for atmospheric processes that influence the spatial and temporal distribution of rainfall.
By explicitly representing aerosol-cloud interactions, the spatial and temporal characteristics of extreme rainfall could be captured more effectively, thereby improving flood inundation simulations, he said.
Prof S N Kuiry of the Department of Civil Engineering, IIT Madras, said rainfall forecasting in a megacity such as Chennai could not be considered separately from water-resources management.
The timing and spatial distribution of extreme rainfall directly influence runoff, reservoir inflows and flood forecasting, and a coupled atmosphere-hydrology-hydraulic framework could provide a more physically informed basis for such decisions, he said.
The researchers said the framework was not yet an operational flood-forecasting system and further studies were needed to determine whether the improvements observed during the 2015 Chennai event could be replicated for other extreme rainfall events and in other cities.
They also highlighted the need for better high-resolution observations of atmospheric aerosols, CCN and urban emissions to improve model representation and validation.
The study was supported by the Asia-Pacific Network for Global Change Research (APN).
The researchers said the approach could eventually be explored in other rainfall-prone megacities facing rapid urbanisation, intense precipitation and limited water-storage capacity.
