Kerala is a strip between a wall of mountains and the sea, and the wall has a single door

Some states are understood by looking at their capital and others by looking at a cross-section. Kerala is the second kind: a very long, very narrow strip squeezed between the sea and a wall of mountains, and everything that happens to it comes from that geometry.

The numbers say it plainly. The coast measures 590 kilometres. The state's width varies between 11 and 121 kilometres. At its narrowest, you cross from sea to mountain in the time it takes to have breakfast.

01 A strip eleven kilometres wide

That strip divides into three parallel bands, and all three can be seen in a single day's travel. In the east, the highlands: rugged, cool mountains with gorges and deep-cut valleys. In the centre, rolling hills. In the west, the coastal plain.

The thermal contrast between the extremes is complete. Up in the highlands it is cool all year and the landscape is arranged in tea terraces. Down below, less than a hundred kilometres away, the daily mean temperature sits around 27 degrees all twelve months of the year.

02 The wall

The Western Ghats are no ordinary range. They rise to an average of 1,500 metres and their highest peaks reach around 2,500; Anamudi, in Idukki district, reaches 2,695 metres and is the highest summit in South India.

What matters is not the height but the continuity. It is a wall running parallel to the coast for hundreds of kilometres without any interruption worth mentioning, and that continuity turns the range into a climatic frontier, not merely a geographical one.

Its forests are considered older than the Himalaya, and the chain ranks among the planet's eight hottest hotspots of biodiversity, as well as being inscribed on the World Heritage List. A barrier that has stood that long accumulates species found nowhere else.

03 The door and where it came from

And here comes the exception. The wall breaks near Palakkad, and that break is 32 kilometres wide: a gap between the Nilgiri Hills to the north and the Anaimalai Hills to the south, connecting the coast with the interior of the peninsula.

Where that gap came from is an open argument, and it is worth telling as it stands. A 2008 study interpreted it as the continuation of a Precambrian shear zone running from East Africa to here, by way of the Ranotsara gap in Madagascar.

Another study, from 2019, proposed that it was opened by a meteor strike between 800 and 550 million years ago, which would have flattened the terrain in the area. And a third hypothesis attributes it to a landslide caused by the river that runs through it today, the Bharathappuzha. There is no consensus.

What is not in dispute is what the gap has meant for people. An ancient highway ran through it, the Rajakesari Peruvazhi, joining the two sides and forming part of a trade route that ran from Muziris on the west coast to Arikamedu on the east. Today a national highway and two railway lines pass through it.

04 What goes in and out through it

The climatic effect is the most striking. During the southwest monsoon the Ghats block the moist air arriving from the Arabian Sea and force it to unload on the western side; beyond them lies a rain shadow that leaves much of the interior of the Deccan plateau dry.

But through the gap that moist air does get across. The result is that western Tamil Nadu, just on the other side, receives more rain than the rest of its region and has its late-summer temperatures moderated. An opening 32 kilometres wide waters an entire territory.

And it works both ways, which you notice travelling through eastern Kerala. Through the same gap come hot winds from Tamil Nadu, which warm that band of the state considerably more than the rest, and tropical cyclones from the Bay of Bengal can slip through as well.

One figure sums it up: the gap records an average annual wind speed of 18 to 22 kilometres an hour, which is why it is one of the region's main areas of wind power generation. Air has been passing through that hole for millions of years and is now being charged a toll.

05 Forty-four rivers and not one long

The combination of wall and narrow strip produces a very characteristic river network. Kerala has 44 rivers, of which 41 run west and only 3 east. Almost all rise on the western side of the Ghats, a short distance from the sea.

And so they are short. The Periyar, the largest, measures 244 kilometres; the Bharathapuzha, 209; the Pamba, 176. The average length of the state's rivers is 64 kilometres. Many are fed entirely by monsoon rain and lack deltas, which makes them especially sensitive to any disturbance.

On reaching the bottom, that water does not simply flow out. The coast is criss-crossed by an interconnected network of brackish canals, lakes, estuaries and rivers running parallel to the sea, known as the backwaters. Vembanad, India's longest lake, covers around 200 square kilometres between Alappuzha and Kochi.

The figure that puts this in scale: around eight per cent of all India's waterways are in this state, which occupies a tiny fraction of the country. It is the final consequence of having a very high range very few kilometres from the sea.

06 What this changes when you travel

The first practical consequence is that here you do not have to choose between mountains and coast. With the strip measuring between 11 and 121 kilometres, climbing from the plain to 1,500 metres is a half-day journey, not a leg of the trip.

The second is that the east of the state is worth understanding as a zone apart. The band level with the gap receives hot air from the other side and is noticeably warmer than the rest, so how the heat feels changes depending on where along the line you are.

And the third is about perspective. When you stand on the plain looking inland and see that green wall closing the horizon, keep in mind that it is not a backdrop: it is the reason there are 44 rivers, a network of navigable lagoons and a climate that looks nothing like the territory immediately behind it.