Uttar Pradesh received 66.5 mm of rain against a normal of 7.6 mm — 775% above normal — turning a heavy monsoon spell into a deadly disaster that has killed 81 people. But why did this particular downpour prove so lethal?

Meteorologists point to an active monsoon trough combined with a low-pressure system that stalled over the state, dumping days of rain in a short window. When that much water falls that fast, rivers overtop their banks and drainage systems in towns and cities are overwhelmed within hours.

The human toll is worsened by fragile housing in low-lying areas; between 1,021 and 2,254 houses have been damaged. Floodwaters also cut off roads, slowing rescue teams.

Experts say such extreme rainfall events are becoming more frequent as a warming atmosphere holds more moisture. The state has placed 23 districts on red and yellow alerts and shut schools through September 30, with the death toll at 81 and still rising. Disaster management experts say the episode underlines the need for better urban drainage and early-warning systems as extreme rainfall becomes more common. Residents are advised to avoid flooded roads and follow district advisories until waters recede.