Which Seoul Neighborhoods Have No Shade?

On August 7, the Deputy Prime Minister for Economy visited the jjokbang district — single-room occupancy housing — in Changsin-dong. That same day an outlet spent a day in the neighborhood and ran the piece as "the shade of polarization, cast by the heat."

One resident said this:

The Changsin-dong area is short of shade in the data too. Changsin 2-dong, within it, ranks last of all 420.

We divided Seoul's 6,584 km of streets into 20-meter intervals, sampled roughly 330,000 points, and counted whether a street tree stood within 15 meters of each. Between neighborhoods the difference was 3.8 times. But look inside the neighborhoods with no shade, and it was not that nobody planted trees. There was nowhere to put them.

We laid the 281,760 street trees from Seoul's 2024 survey over the street network. Of the 330,000 points, 25.6% had a tree within 15 meters.

The average matters less than the gap between neighborhoods.

Same city: in one neighborhood nearly half the walk has a tree beside it, in another about one stretch in eight.

We cut the bottom quarter and grouped them: 106 neighborhoods at 17.3% coverage or below. They had something in common.

These were neighborhoods packed with low, small houses. Building density was roughly double that of the rest of the city, and 83.5% of their streets were alleys.

Why?

Planting a street tree is not dropping a sapling into empty ground. Under Seoul's standards, a tree needs:

"An empty spot where a tree fits" is not enough. In a narrow alley these conditions rarely hold at once.

So trees cluster on the wider streets.

Wider streets are only 31% of Seoul's network but hold 78% of its street trees — 84 per km against 11. Some neighborhoods have few trees not only for want of budget or will, but because there is little street to plant on.

We went back to the 106 bottom neighborhoods, this time counting only the streets worth planting^?. These are the top three street classes.

Look only at those streets and most of them already carry trees — 96.8% in Gusan-dong, 85.5% in Samyang-dong, 80.0% in Dasan-dong. Yet coverage across the whole neighborhood stays at 7–16%.

Those streets are only 5–8% of the neighborhood's roads. Trees are not missing where they should be. There was almost nowhere to put them.

In some neighborhoods those streets were too short to compute a rate at all: Changsin 2-dong, Changsin 3-dong, Sadang 4-dong, and Donghwa-dong. In Changsin 2-dong they came to 0.2% of 7.5 km — effectively none.

Planters, small green patches and the space along a wall do exist on the ground, and this analysis does not see them. But planting street trees along the streets that are already there cannot fix these neighborhoods.

The numbers behind the opening: street-tree coverage 0.0%, midday building shade 2.4%, streets worth planting 0.2%.

Heat in a dense low-rise neighborhood is not only about "the sun being hot." With no shade, walls take sun all day and heat up; with a narrow alley, that heat has nowhere to go. You do not have to be standing in the sun to be taking heat from every wall around you.

That is what the resident meant by "the heat never leaves the room." The walls do not cool at night, so neither does the room.

So what do you do where a tree cannot go?

There is a useful precedent. Since 2016, Medellín, Colombia has built out Green Corridors (Corredores Verdes), linking streets and waterways.

What matters is that the program did not stop at increasing the count of large trees. Along streets and water edges it layered shrubs and ground cover alongside canopy trees, and where trees were hard to plant it used planting beds and vertical greening. Rather than ending at "plant trees where trees can be planted," it extended greenery across multiple layers and forms.

Seoul's narrow alleys can draw on the same approach. Not every alley can hold a large street tree — but that does not mean those spaces cannot hold greenery at all.

Plants on a wall do not lower air temperature much. Across studies the outdoor effect is small.

The effect is elsewhere. It is radiant heat.

How hot we feel is not decided by one number on a thermometer. If a wall beside you is radiating heat, you feel hotter at the same air temperature — and a narrow alley is walls on both sides.

Cover the wall with plants and it stops taking direct sun; leaves and soil work as insulation. Air temperature barely moves, but the heat reaching a person falls. Studies have measured mean radiant temperature dropping at pedestrian height.

Not every answer is greenery. After a 2010 heatwave killed more than 1,000 people beyond the usual toll, Ahmedabad, India built a heat action plan — and put cool roofs in it. A reflective coating on the roof cuts the heat entering the rooms below. The 2017 program set out to reach 3,000 low-income households.

The cost is what stands out. Reflective paint was used on only 10 to 15 pilot homes; the rest of the roofs were finished with three coats of lime. Low-rise buildings take in up to a fifth of their heat through the roof, which makes the roof a place where a small budget still buys something.

Seoul has already applied it in places. The city subsidizes heat-reflective roof coating, and this year it covered 204 sites across older residential areas in Dongdaemun, Jungnang, Seongbuk and Nowon on a budget of 1.3 billion won. Several of the neighborhoods this analysis found short of shade sit in those districts: Jangwi 1-dong in Seongbuk (3.6% coverage, third lowest of 420), Jeongneung 3-dong in Seongbuk (10.2%) and Myeonmok 3·8-dong in Jungnang (10.3%).

In field testing^? on SH apartment buildings, rooftop surface temperature fell by up to 9.2°C and indoor temperature by about 1.8°C.

The neighborhoods with the least shade were not missing trees. The streets that could hold trees already had them. There were just almost no such streets.

This is different from a budget problem. A neighborhood short of money can be given more money; a neighborhood short of space cannot be given more space. Multiply Changsin 2-dong's planting budget by ten and there is still only 0.2% of 7.5 km to plant on.

So what is worth trying differs by neighborhood.

Street trees are not the only answer. There are several approaches that take up little room, and other cities have already put them to use. A neighborhood of nothing but alleys can pick whichever of them fits and give it a try.

The "street-tree coverage" used here is not a direct measurement of actual shadow. It estimates the potential for tree shade from whether street trees are present around a sample point. The real position and size of shade varies with time of day, season, solar altitude, crown size, and street orientation.

Building shade was computed only for the 12 neighborhoods with the lowest street-tree coverage, not for the whole city. The building register carries no coordinates, so individual buildings could not be tied to map positions; height distributions at the legal-neighborhood level were used instead.

Alley width was estimated as the distance from the street centerline to the nearest building on each side, so it does not exactly match sidewalk width and may include yards or building setbacks.

The "streets most likely to be plantable" measure is likewise an estimate from street hierarchy rather than a field survey of plantability. Actual planting is further constrained by sidewalk width, utility poles, streetlights, crosswalks, and vehicle access.

Green-wall effects draw on studies from Hong Kong, Singapore, Turin, and other cities; they are not values measured in these specific Seoul alleys.