Why are summers in the city dangerous? Heatstroke prevention for urban heat islands and reflected heat
“When I go back to my parents' home in the suburbs, the same temperature feels easier to bear.” Have you ever felt this? It is not your imagination. Summer in the city is different in kind from summer in the suburbs. City heat also has its own particular difficulty: heat that comes from below and from the side, which a parasol or a hat alone cannot fully block. This article explains heatstroke prevention for people who live and work in cities.
Why cities are hotter than suburbs: the “heat island” effect
The phenomenon in which temperatures in city centers are higher than in the suburbs is called the “heat island” effect. Its main cause is asphalt and concrete covering the ground, which store daytime heat and keep releasing it.
Soil and green ground release heat through the evaporation of water. Asphalt and concrete, on the other hand, contain no water, so evaporative cooling does not work, and they store the energy of sunlight. Add the exhaust heat from air-conditioner outdoor units and cars, and the whole city becomes an “island that stores heat.”
On a clear midsummer day, asphalt surface temperatures can reach 50–60°C, far above the air temperature. City sidewalks are, in effect, a huge heat-storage plate.
City-specific risk 1: heat from below — reflected heat
Even if a hat or parasol blocks direct sunlight from above, reflection and re-radiation from the hot road surface keep heating the body from below.
Reflected heat includes both sunlight reflected by the road surface (including near-infrared rays) and the heat released by the road surface itself. The face, the neck and the lower part of the torso are almost unprotected against this heat from below. Children in strollers and small dogs are said to be at greater risk than adults because the closer to the ground, the more strongly they are exposed to this heat.
“I'm using a parasol, but somehow I feel exhausted.” One possible reason is the heat received from below and from the side.
City-specific risk 2: temperatures that stay high at night and accumulated heat fatigue
Another feature of city heat is that the temperature does not drop easily even at night.
Heat stored in buildings and roads during the day continues to be released slowly after sunset. When hot nights continue, the body cannot recover during sleep, and fatigue and heat stress accumulate from one day to the next. Behind cases of heatstroke in cities where people collapse “even though it wasn't an especially hot day” lies this daily accumulation. The risks of starting the next day without core body temperature having fully come down are explained in “What is core body temperature?”
City heat measures for commuting and walking around town
City heat measures come down to three ideas: reduce the heat you are exposed to, avoid storing it in your body, and make sure you recover.
1. Choose your route and time Even over the same distance, the amount of heat you are exposed to on sunny asphalt is completely different from the shade of buildings, underground malls or arcades. A detour of a few minutes along a shaded route is worth it. If possible, go out in the morning before the road surface has fully stored heat.
2. Dress with heat from above and below in mind Blocking direct sunlight from above with a hat or parasol is the basic step. On top of that, choosing clothing that covers your skin, including against reflected heat, is one option. Note that the usual UV-protection labeling covers UV rays (about 5% of sunlight), and near-infrared rays are outside its scope (for details, see “What is near-infrared light?” and “How to choose heatstroke prevention innerwear”).
3. Drink water and take salt “before you move” Instead of “I'll drink when I get to the station,” take a sip before you start walking. City travel often follows a pattern of large swings in heat — walk for 10 minutes, cool down on the train, then walk for another 10 minutes — and frequent hydration reduces the burden on temperature regulation.
4. “Reset” with your sleeping environment On hot city nights, bedroom temperature control affects the next day's heatstroke risk. Not holding back on air conditioning and letting the body recover until morning is also a legitimate heatstroke measure.
Near-infrared-cutting innerwear that covers the torso
Our store's CORE SHIELD® is Japanese-made innerwear that handles both near-infrared and UV rays. Using Trubeaute®, a special fiber with special ceramic microparticles derived from rare metals kneaded into it, it blocks 87%+ of near-infrared rays (White 88.6% / Black 87.6%; measured on the fabric alone by the material manufacturer).
It covers the torso, which a parasol or hat cannot cover, with fabric, whichever direction the sunlight comes from. For commuting and outings, its cool-touch and moisture-wicking, quick-drying properties also help keep sweat from feeling sticky.
Summary
- Cities are hotter than suburbs because asphalt and concrete store heat (the heat island effect)
- Hats and parasols cannot block reflected heat from the road — “heat from below”
- Temperatures that stay high at night make heat fatigue build up day by day
- Measures: shaded routes and timing, clothing that considers heat from above and below, drinking before you move, and recovering through sleep
- Be aware of covering the torso, including against reflected heat
City summers put more strain on the body than the day's maximum temperature suggests. Understand the structure of the city itself and get through the summer wisely.
