Climate · InfographicOrographic rain
Why there is forest on one side of the range and dry valleys on the other. One mountain, two climates.
Simplified diagram, not to scale. The height of the range is exaggerated. Credit: E. Guido (Lluvias orográficas)How to read the illustration
You are looking at a slice of the mountain, from east to west. The Chaco plain is on the right and the Santa María valley on the left. The blue arrow is the humid wind and the orange one is the same wind, now dry. The slanted lines are rain, the white dots are snow and hail, and the clouds mark where the water condenses. The numbers follow the air from right to left.
- Humid wind. Air loaded with water vapour arrives from the east, coming from the Atlantic across the plain.
- Rising and cooling. The mountain forces the air upwards. The higher it goes the colder it gets, and the vapour condenses into droplets.
- Clouds, rain and snow. Clouds form on the Tucumán slope and rain falls on the forest, mostly in summer. Higher up, where it is colder, snow and hail fall.
- Dry descent. Past the summit the air has lost most of its water. It sinks, is compressed and warms up, and reaches the valley dry. This is the rain shadow.
Why it matters
The Yungas exist because the mountain traps the moisture. That rain and fog feed the forest, the streams and the rivers that run down to the plain. On the far side of the range, with the air already dry, cacti, scrub and high-altitude deserts appear, very close by. It is also why the cloud belt of the montane forest matters so much.
See the ecoregions →See the altitude floors →
CreditThis illustration is based on the “Lluvias orográficas” diagram by E. Guido (source credited on the original diagram). The artwork was redrawn for this atlas and simplified.