Houston has a July average high temperature of 34,7 degrees C with an average relative humidity of 74,4. The same data for Taipei is 34,3 degrees C with a humidity of 73.
Yet Houston has a population density of 1398,76/km2 whereas Taipei 9700/km2, almost 7 times as high.
Data from Wikipedia.
Actually, perhaps this map says it best: https://www.dropbox.com/s/tkoekp0or12ppjc/Screenshot%202020-...
(If anything, building densely can create a lot of shade, which can be quite beneficial.)
The population of Taiwan[1] is 23.78 million, and its land area is 35,808 km^2. The population of Texas[2] is 29 million, and its land area is 676,587 km^2.
So Taiwan has nearly (82%) as many people but 1/20th the land.
Also, Taipei is boxed in by large mountains and the ocean, so there are lots of natural barriers discouraging sprawl.
Houston is near the ocean, but aside from that there are no natural barriers. The land around it is super flat in every direction. The closest hill of any size is probably 150 miles away.
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Siena seems to have a very mild climate. Its average high temperature[1] in August is 28.3°C (82.9°F).
Compare that to Houston's monthly high for August, which is 35°C (95°F). Houston is also very humid[3].
Most people don't want to take a 10-minute walk when it's 95°F and humid. You arrive at your destination panting and very sweaty. It's more comfortable to take a 10-minute drive in an air conditioned car. To some people, it's preferable even if the drive takes 30 minutes due to traffic.
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[1] https://en.climate-data.org/europe/italy/tuscany/siena-1089/
[2] https://en.wikipedia.org/wiki/Climate_of_Houston
[3] https://finance.yahoo.com/news/america-most-humid-cities-090...