# Urban-resolved scales amplifies torrential rainfall in coastal megacities

## TL;DR

This study shows that high-resolution simulations can better model urban effects on extreme rainfall in coastal cities like Chennai.

## Contribution

The novelty lies in demonstrating how 200-m LES simulations capture urban-induced turbulence and heat island effects to intensify rainfall.

## Key findings

- 200-m LES simulations resolve urban heat flux and wind dynamics better than kilometer-scale models.
- Urban heat island effects and wind interactions intensify heavy rainfall in downwind regions of coastal cities.
- Higher resolution simulations reveal critical factors like moisture transport and surface wind speeds.

## Abstract

This study unveils the ability of 200-m near to Large-Eddy Simulation (LES) to resolve smaller scales in urban areas of a coastal megacity Chennai in India, which are crucial for accurately modelling Urban Induced Turbulence (UIT) and Urban Heat Island (UHI) effects. Unlike physics-based ensemble (PBE) models in kilometer-scale simulations, LES captures fine-scale atmospheric dynamics, offering enhanced resolution to simulate localized turbulence and heat flux variations. With a resolution of 200 m, Weather Research Forecasting (WRF) LES simulation can convincingly resolve a higher urban heat flux, friction velocity, surface wind speeds, and moisture transport over urban areas. These factors are found to play a critical role in intensifying extreme weather events such as heavy rainfall, especially in the downwind regions of coastal megacities like Chennai. This phenomenon is driven by LES-resolved interaction between the urban heat island effect and the prevailing winds.

The online version contains supplementary material available at 10.1038/s41598-025-23906-y.