Lima

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A City with 98% Humidity and Almost No Rain

1. Lima gets under 10 millimetres of rain a year.

Estimates vary between about 7 and 16 millimetres depending on the measuring period, but the picture is consistent: this is one of the driest capital cities on Earth, second only to Cairo. It is also the world's second-largest desert city, again after Cairo.

For comparison, London gets around 600 millimetres. Lima receives roughly one-eightieth of that.

2. And yet the humidity reaches 98%.

The cold Humboldt Current runs up this coast, chilling the air above it. Cold air holds less moisture, so instead of rain the city gets garúa — a persistent grey drizzle-fog that sits over Lima for months at a time.

The result is a genuine climatic oddity: Lima records around 1,230 hours of sunshine a year, fewer than London, despite sitting at 12° south, deep in the tropics. A tropical city, permanently overcast, in a desert.

3. Ten million people drink water that starts as glacier melt above 5,000 metres.

Lima depends on three Andean rivers — the Rímac, Chillón and Lurín — and roughly 80% of its supply comes from the Rímac basin alone. The Rímac rises above 5,000 metres and carries snowmelt and glacial runoff down to a coastal desert.

Retreating Andean glaciers are the long-term risk. In the meantime, fog-catching nets have been strung on hillsides to harvest water from the air, and one engineering university built a billboard that condenses atmospheric humidity into drinking water, storing it in 20-litre tanks.

A city with no rain and 98% humidity has started collecting the humidity.

4. The oldest university in the Americas has been open since 1551.

The National University of San Marcos has operated continuously for 475 years — longer than any other in the hemisphere.

The clock: Lima sits at about 77° west, on UTC−5, which is built for the 75th meridian. The city runs roughly eight minutes ahead of its own solar noon — very well aligned.

Not that anyone can see it. At 12° south the day length barely moves all year, varying only between about eleven and a half and thirteen hours. Combine a sky that does not change with a sun that is usually behind cloud, and you have a city where the passage of the day is signalled mainly by the grey getting lighter and then darker again.

Luz solar anual