• Atmospheric natural variability is the cause of Chennai extreme rains.
• Anthropogenic variability due to urbanization influenced the hydrological cycle to result in extreme rainfall.
• Unprecedented urbanization over Chennai in 2015 modified the hydrological cycle.
• Convective coupled equatorial waves were found to contribute to natural variability.
• Northward propagating ‘tropical disturbance’ triggered extreme rain events along the southeast coast of India.

How to effectively understand urban climate interactions?

Flow chart shown in above figure can give an effective understanding about reasons/factors that cause floods over the metropolitan cities. Above concept in flow chart is applicable over almost all metropolitan cities in the world.