In 1966, on Reunion Island in the Indian Ocean, it rained over 1,800 millimeters – that’s more than 72 inches – in just one day.
But the rainiest place on Earth is probably Cherrapunji, India. Cherrapunji holds many of the world’s rainfall records. The heaviest rain in a single month happened there – 9,300 millimeters – that’s over 360 inches of rainfall.
Rain happens when the sun’s heat evaporates water up into the atmosphere. The water vapor stays in the atmosphere until it cools and condenses, first into clouds and then into raindrops. How hard it can rain depends on the amount of moisture in the air. The atmosphere holds more water if it’s warm, that’s why most places that set rainfall records are in the tropics.
But the main cause of heavy rain is wind patterns that blow atmospheric moisture into the area. In Cherrapunji, India, the seasonal monsoon winds blow in moist air from the ocean. Some of the heaviest rains occur in a hurricane. Here, again, the wind patterns are a key. Rainfall records also often happen in mountainous places. That’s because mountains give an extra boost to the upward motion of the air, cooling it, which speeds condensation.