According to the Koppen climate classification system, for a climate to qualify as tropical, all months need to have an average temperature above 18°C.
Given that Rio's here I expected Sao Paulo to be here too, given they're at basically the same latitude. Are their climates that different, or is it a case of Sao Paulo just barely missing the cutoff?
The difference between their lowest temperatures is actually quite significant: Sao Paulo has an average July temperature of 15.8°C, while Rio's July temperature is 21.3 °C. The reason for this is Sao Paulo's inland location at an altitude of about 800m, in contrast to Rio's coastal location near a warm ocean current.
Actually, Sao Paulo is not that far from the sea, the distance between the city and the Atlantic Ocean is about 100-150km. However, there's an important mountain range (known as Serra do Mar) that blocks a great deal of warmth and humidity that comes from the Ocean.
Alex2108's explanation is very good, though I'd say São Paulo is slightly nearer to the Atlantic Ocean since Santos (São Paulo state's most important coastal city) is circa 75 km from São Paulo.
Non-arid is defined as receiving more annual rainfall than can be lost to the atmosphere through evaporation or transpiration. The latter amount varies from place to place and can be estimated based on the average annual temperature and the distribution of rainfall throughout the year. For the exact method of calculation see here!
Is that why Delhi is not on here? Because I was absolutely shocked when it didn't show up, especially considering that most other major Indian cities did.
for example, big tropical cities that are quite high (La Paz, Bogota, Sana'a, Mexico City...) and cities lying i quite arid regions (which wasn't explicitly mentioned - as oppose to the average temperature part). Still good quiz
I don't think that many of the Indian cities listed here should be on the list. I've visited all of them in winter months except Hyderabad, the weather was cool. Chennai and Bombay might be correct but as for Surat and Calcutta, I'm certain that the temperature falls below 18 degree celsius.
Even if the temperature falls below 18 degrees (during the night or on cool days), what counts is the average temperature, which is above 18 degrees Celsius for every month of the year in each of the cities listed.
It certainly does! The word "tropical" refers to anything relating to the area between the tropics, not just around them. A tropical climate has certain characteristics (see the quiz instructions) that are typically found in most places near the equator.
Altitude matters. We once left the coast of El Salvador with the temperature being just about right at 36°C. We reach Antigua, Guatemala in the evening at the height of 1500m. As the bird flies, it was less than 200km's but the temperature dropped like over 20 degrees. We've never been so cold in our lives.