In Salta it rains three thousand millimetres at one end and a hundred at the other
The province is ordered in three parallel strips: montane rainforest to the east, dry valleys in the middle and puna to the west. Between the first and the last there is a thirtyfold difference in rainfall, and a single cause: the ranges the air has to cross.
Salta covers 155,488 square kilometres and has a little over 1.4 million inhabitants. But what defines the province is not its size: it is that it is organised in vertical strips, and that crossing them from east to west means passing through three different worlds in a few hours of driving.
The cause of that organisation is air, and you can follow it with a finger on the map.
01 Three parallel strips and a single cause
Damp air reaches Salta from the east, from the Chaco plain, which is flat and low. It travels unobstructed for hundreds of kilometres until it meets the first relief: the sub-Andean ranges, the province's eastern edge.
There it is forced to rise. On rising it cools, on cooling it cannot hold the vapour it carries and releases it as rain and fog. It is the simplest mechanism in mountain meteorology and here it produces an extreme result.
Because behind that first range there is another, and another, and the air reaches each one with less water than the one before. By the time it reaches the altiplano, it has practically nothing left to release.
02 The first range keeps almost everything
The eastern strip is called yungas, and it is montane rainforest: a dense cloud forest with several superimposed vegetation levels and tree ferns. In Baritú National Park, in the far north, rainfall reaches something of the order of 3,000 millimetres a year.
In El Rey National Park, further south and covering 44,162 hectares, the figure is around 2,000 millimetres. Overall, the yungas region receives between about 900 and about 2,500 millimetres depending on the spot and the altitude.
And the yungas itself is ordered in tiers by the same logic. The piedmont forest, between about 400 and 700 metres, gets under a thousand millimetres; above 500 the montane forest begins, and higher still the montane woodland and the high-altitude grassland.
03 The middle valley, which lives on what gets through
The central strip is the valleys: the Lerma valley, where the city of Salta sits at 1,187 metres, and the Calchaquí valleys, further west and higher. Here the figure drops sharply.
The Salta airport station records 738.3 millimetres a year over 88.6 rainy days. That is a quarter of what falls in Baritú, and the city is less than two hundred kilometres away as the crow flies.
One step further west, in the Calchaquí valleys, the decline continues and the landscape changes category: spaced scrub, bare soil between clumps and rock on show. The Quebrada de las Conchas, on the way to Cafayate, displays its strata in colour precisely because there is no vegetation covering them.
04 And the puna, where nothing arrives
The western strip is the puna, the altiplano. The San Antonio de los Cobres station, at 3,775 metres, records 103.9 millimetres of rain a year. Almost all of it falls in summer: 44.0 millimetres in January and 0.0 in July.
A hundred and four millimetres is less than parts of the Sahara collect, and it explains why vegetation here is sparse and low, and why the ground shows between plant and plant from any angle.
Temperatures complete the picture: in January, the average maximum is 20.4 degrees and the minimum 4.2; in July, 11.9 and −7.7. Cold, dry and with the radiation of nearly four thousand metres of altitude.
05 Six thousand metres of vertical range
The other way to measure the province is from the bottom up. The eastern end, on the Chaco plain, is a few hundred metres above sea level. The Nevado de Cachi, in the west, reaches 6,356 metres.
That six-kilometre vertical range is what makes Salta work like a sample case. Each altitude tier has its own vegetation, temperature and rainfall regime, and the tiers are stacked one above another instead of spread across a continent.
And it explains something that surprises you on arrival: that on the same day you can be in a forest hung with lianas in the morning and in a high desert in the afternoon, without covering more ground than you would between two neighbouring cities anywhere else.
06 How to travel it
The first practical consequence is that the roads worth taking are those crossing the strips, not those running parallel to them. Climbing from east to west shows the whole mechanism in a single day.
The second is that the change is not gradual. Between the last forested slope and the first dry valley there are sometimes only a few kilometres, and the cut is visible from the car: the forest ends in a line and scrub begins behind it.
And the third affects packing. Crossing Salta from end to end means going from 25 degrees and high humidity to sub-zero nights at four thousand metres. It is not a destination with one climate: it is a destination with three, and you visit all of them on the same trip.
