Why do heavy summer rains sometimes cause floods and landslides in Rio de Janeiro?

In Rio de Janeiro, catastrophic floods and landslides during the summer months (December–March) are primarily driven by the city's unique topography.

The city's mountainous terrain acts as a physical barrier to the humid wind blowing in from the Atlantic Ocean. As these moisture-laden winds are forced upward by the coastal mountains, they cool and condense, resulting in intense rainfall. This effect is particularly pronounced in areas like the Jardim Botânico district, where the mountains effectively trap the humid air, leading to higher precipitation rates. When these strong summer showers occur, the combination of heavy rainfall and steep, mountainous slopes creates the conditions necessary for dangerous landslides and flooding throughout the urban landscape.1