Why does it almost never rain in Lima?

The Humboldt Current. Cold water flowing north up the coast chills the air above it, which produces a stable layer that suppresses convection - so moisture condenses into a persistent grey overcast and drizzle that Limeños call garua, and almost never into rain. The city averages a few millimetres a year and sits in a desert while being permanently damp and cloudy.

It is the second largest desert city in the world after Cairo, and its water comes almost entirely from rivers fed by Andean glaciers - which are retreating. Some districts have relied on fog-catching nets, large mesh screens that condense the garua into drinking water, which works precisely because the air is saturated and the rain never falls.

The same current is why Peru had one of the world's great fisheries. Cold upwelling water carries nutrients to the surface and supports enormous anchovy stocks - Peru has at times landed more fish by weight than any country on Earth. El Niño reverses the upwelling periodically, the anchovies vanish, the seabirds starve, and the rain that never comes to Lima falls in torrents. The phenomenon is named for the Christ child because it typically arrives around Christmas.