Altitude and the sea

Altitude (height) is the second factor. Hill stations like Munnar, Ooty (Udhagamandalam), Madikeri, Mahabaleshwar, Mount Abu, Shimla, Nainital, Darjeeling, Tawang and Shillong are popular because they're cooler.

Temperature falls as you go higher, because:

• the air gets thinner (lower pressure), and thinner air is cooler
• the Sun heats the ground, so air far above the ground is less warm

Many Himalayan peaks stay below freezing and are always covered in snow.

Ooty and Coimbatore are at almost the same latitude, but in summer Ooty is 10–25°C and Coimbatore 25–38°C. The difference is height.

Third factor: nearness to the sea. On the coast, temperatures don't swing much: summers aren't too hot, winters aren't too cold. The sea moderates them. Why? Land heats up and cools down quickly; the sea heats and cools slowly. So sea air cools the coast in summer and warms it in winter.

Imagine you live by the sea and your friend lives far inland. On the same summer day she phones: It's boiling here! You say: It's fine here! You're both right: the sea is keeping you mild.

Move inland and temperatures get more extreme. Mumbai and Nagpur are at a similar latitude:

The sea doesn't just cool: it evens out the temperature.