In Chiapas you go from the beach to 4,080 metres in about sixty kilometres
Chiapas is built like a staircase set against the Pacific. That explains why the capital gets half the rain the coast does, why two cities an hour apart are twelve degrees apart, and why 3.8 per cent of the country holds 11,223 species.
Almost every Mexican state can be summed up by its climate. Not Chiapas, and not because it lacks one, but because it has too many at once. In the same territory there is mangrove, rainforest, cloud forest, mountain pine wood and dry scrub, and the distance between them is measured in minutes of driving.
The reason is not latitude, which barely changes, nor distance from the sea, which is short. It is height. Chiapas is built like a staircase set on edge against the Pacific, and almost everything you see here depends on which step you are standing on.
01 A staircase, not a plain
The state's physiographic classification recognises seven regions, and the interesting part is that they are arranged in bands almost parallel to the coast. You climb them one after another as you move inland.
First the Pacific coastal plain, flat and hot, at sea level. Then the Sierra Madre de Chiapas, the barrier running alongside the ocean and topping out at the Tacaná volcano, 4,080 metres, the highest point in the state. Behind the range, the Central Depression, a long low valley. Then the Altos, the plateau above 2,000 metres. And finally the northern and eastern mountains, dropping towards the forested lowland.
From the Pacific shore to the summit of Tacaná there are about sixty kilometres in a straight line. Four thousand metres of relief over that distance is a gradient equivalent, in practice, to travelling vertically the climatic distance that separates the tropics from high mountains.
02 Why the middle is the dry part
The first consequence of the step is counterintuitive. Chiapas is one of the rainiest states in Mexico, and its capital is one of the driest parts of the state.
The numbers say it unambiguously. In Tapachula, on the coastal plain, 2,057.8 millimetres fall a year over 146.0 days. In Tuxtla Gutiérrez, in the Central Depression, at 532 metres and little more than a hundred kilometres away, 1,053.6 millimetres fall over 92.6 days. Half the water and two thirds of the days.
The mechanism is the same as in any coastal range. Humid air arriving from the Pacific has to climb the Sierra Madre, cools, condenses and unloads on the seaward flank. When it crosses the crest and comes down the other side it is already dry and warms as it descends. The Central Depression lives in the shadow of that barrier.
That is why on the floor of that depression there is dry deciduous woodland, cactus and trees that drop their leaves in the dry season, a landscape nobody associates with Chiapas, and less than an hour away there is cloud forest.
03 Twelve degrees in an hour's drive
The second effect is thermal and the easiest to check. Tuxtla Gutiérrez sits at 532 metres; San Cristóbal de las Casas at a little over 2,100. Some fifty kilometres separate them in a straight line and a bit more than an hour by road.
In April, the hottest month, Tuxtla's average high is 36.1 degrees and San Cristóbal's is 24.0. That is 12.1 degrees of difference. In January, Tuxtla's average low is 16.1 and San Cristóbal's is 4.9.
The extremes pull the two cities further apart still. Tuxtla has recorded 42 degrees; San Cristóbal, −7.5 in March 1991. One is in the hot tropics and the other needs a fireplace in winter, and both are Chiapas.
04 The consequence: almost everything fits here
Adding up so many climates in so little space has a measurable result. Chiapas occupies around 3.8 per cent of Mexico's surface and some 11,223 species have been recorded in it, against 29,429 for the whole country.
With birds the concentration is more striking still: with 694 recorded species, it is the state with the richest list in Mexico. According to the national biodiversity commission, Chiapas and Oaxaca between them hold close to a quarter of the country's plant and animal species.
The explanation is the staircase. Each altitude band supports a different community, and because the bands are stacked within a few kilometres, the state accumulates inside itself what elsewhere is spread over thousands of kilometres of latitude.
05 Water comes down the steps too
The third effect of the relief is hydrological, and it is the one that gives Chiapas its role within Mexico. All the water dumped on the high flanks has to come down, and it does so through short, steep channels.
Two things a traveller notices at once come from this. One is the waterfalls: geological steps produce cascades in series wherever a river crosses an abrupt change of rock. The other is the Sumidero Canyon, a gash with vertical walls cut by the Grijalva river exactly where it crosses the range.
That same relief is what made the state a key piece of the Mexican electricity system: abundant flow plus a rapid drop is, literally, the definition of a good hydroelectric site.
06 How to travel it
The first practical consequence is that you pack by altitude, not by destination. A normal trip through Chiapas goes from 30 degrees to 10 in the same day, and warm clothes are not optional however tropical the map looks.
The second is that distances lie. In a territory of steps, the road climbs and drops in continuous bends, and a hundred kilometres can be three hours. Reckon in time, never in kilometres.
And the third reorders the whole itinerary: instead of hopping between famous places, it pays to follow one complete cross-section, from the sea upwards or from the Altos down. Done that way, the state stops being a list of loose places and becomes what it really is: a staircase you climb.
