Geography of Seoul: South Korea's Capital in the Han River Valley

Seoul, the capital of South Korea and home to roughly 9.7 million people (25.5 million in the Seoul National Capital Area), sits in a broad basin along the Han River, surrounded by mountains on all sides. The Han River, 494 km long, bisects the city east to west, creating a distinct northern half (Gangbuk, "north of the river") and southern half (Gangnam, "south of the river").

Introduction

Seoul's mountain-ringed geography has shaped the city for over 600 years, since the Joseon Dynasty chose this site for its capital in 1394 precisely because the surrounding mountains provided natural fortification. The city covers 605 km² and is remarkable for the extent to which mountains and green space penetrate the urban fabric—despite its extreme density, roughly 40% of Seoul is mountainous parkland.

Location & Setting

• Coordinates: 37.5665°N, 126.9780°E
• Elevation Range: 20–836 m (Bukhansan peak)
• Area: 605 km²
• Country: South Korea

Seoul sits in the Han River valley roughly 50 km south of the Demilitarized Zone (DMZ) separating North and South Korea and roughly 40 km inland from the Yellow Sea coast. The city occupies a natural basin surrounded by mountains: Bukhansan (836 m) to the north, Gwanaksan (632 m) to the south, and numerous smaller peaks forming a ring around the urban area.

The Han River enters Seoul from the east, flows west through the city in a broad valley (roughly 1 km wide through the center), and exits to the northwest toward the Yellow Sea. Several tributary streams flow from the surrounding mountains into the Han, including the Cheonggyecheon, a famous stream that was buried under a highway in the 1960s and then dramatically restored as an urban park in 2005.

Terrain & Landscape

• Bukhansan: 836 m, granite peaks in a national park within city limits
• Gwanaksan: 632 m, forested mountain on the southern boundary
• Han River Valley: Broad floodplain, 1+ km wide through the city
• Urban Mountains: ~40% of Seoul is mountainous green space

Seoul's terrain is dramatic for a city of nearly 10 million. Mountains and hills punctuate the urban landscape, with many peaks accessible by short hikes from subway stations. Bukhansan National Park, entirely within the Seoul metropolitan area, covers 80 km² of granite peaks, pine forests, and Buddhist temples. It is one of the most visited national parks in the world, receiving roughly 5 million hikers annually.

The Han River floodplain and its tributary valleys provide the flat land where most of Seoul's development is concentrated. The river's banks have been developed into extensive public parks (the Hangang Parks) stretching over 40 km along both sides, featuring walking paths, bike trails, swimming pools, and recreational areas—one of the world's great urban riverfront parks systems.

Climate & Weather

• Climate Type: Humid subtropical/continental (Köppen Dwa)
• Average Summer Temp: 23–30°C, with monsoon humidity
• Average Winter Temp: -6–2°C, Siberian cold waves
• Annual Precipitation: ~1,400 mm, 60% in June–August

Seoul has one of the most extreme climates of any major world city, with hot, humid summers and bitterly cold, dry winters. The East Asian monsoon dominates summer weather (June–August), bringing roughly 60% of the annual 1,400 mm of precipitation in three months. This concentrated rainfall regularly causes flooding along the Han River and its tributaries, and landslides on the city's many mountainsides.

Winter brings cold, dry air from Siberia, with January temperatures averaging -6 to 2°C and cold snaps pushing below -15°C. The annual temperature range of roughly 30°C (from -10°C in January to 30°C+ in July) is among the widest for any major city. Yellow dust (hwangsa) from the Gobi Desert, carried by westerly winds, occasionally blankets Seoul in spring, creating air quality alerts.

Han River & Waterways

• Han River: 494 km total, bisects Seoul east–west
• River Width: Up to 1+ km through central Seoul
• Cheonggyecheon: Restored urban stream, 5.8 km through downtown
• Flood Control: Major dam (Paldang) upstream, levees through the city

The Han River is Seoul's most important geographic feature, dividing the city into Gangbuk (north bank—the historic core) and Gangnam (south bank—the modern business and residential districts). The river is wide and slow through the city, controlled by the Paldang Dam 40 km upstream and confined by levees and flood walls within Seoul.

The restoration of Cheonggyecheon is one of the most celebrated urban geography projects in the world. A 5.8-km stream that had been paved over and covered by an elevated highway in the 1960s was dramatically restored in 2005 by removing the highway and creating a linear park. The project reduced local temperatures by 3–5°C, improved air quality, increased biodiversity, and became a model for urban stream restoration worldwide.

Geology & Natural Hazards

• Bedrock: Granite and gneiss (Precambrian)
• Seismic Risk: Low but not zero; occasional felt earthquakes
• Landslide Risk: Significant during monsoon season on steep slopes
• Flood Risk: Major; Han River flooding, urban flash floods

Seoul sits primarily on Precambrian granite and gneiss, extremely hard rocks that form the backbone of the Korean Peninsula. The granite peaks of Bukhansan and other mountains are dramatic exposures of this ancient rock. The Han River valley is filled with alluvial sediments that provide the flat building land but can amplify seismic waves.

The Korean Peninsula is relatively seismically quiet compared to Japan, but damaging earthquakes do occur. The 2016 Gyeongju earthquake (magnitude 5.8) was the largest instrumentally recorded in South Korea and was felt in Seoul. Landslides during the monsoon season are a regular hazard on Seoul's many mountainsides; the 2011 Umyeonsan landslide killed 18 people in a residential area on the southern outskirts.

Key Facts

• Seoul sits in a mountain-ringed basin along the Han River, with ~40% of the city being mountainous parkland.
• The Han River (494 km) bisects Seoul, creating the historic Gangbuk (north) and modern Gangnam (south).
• About 60% of annual rainfall (~1,400 mm) falls in the three summer monsoon months.
• Bukhansan National Park (80 km²) receives ~5 million hikers annually within the metropolitan area.
• The annual temperature range of ~30°C is one of the widest for any major world city.

Fun Facts

• The Cheonggyecheon stream was buried under a highway in the 1960s and dramatically restored as a park in 2005.
• Bukhansan's granite peaks are Precambrian rock, among the oldest exposed surfaces in the region.
• Yellow dust from the Gobi Desert occasionally blankets Seoul in spring, carried by westerly winds.
• The Joseon Dynasty chose Seoul as its capital in 1394 because the surrounding mountains formed a natural fortress.

Final Thoughts

Seoul's geography is defined by the interplay of mountains and river. The surrounding peaks that made it an ideal fortress-capital 600 years ago now provide remarkable green space for a megacity of 10 million, while the Han River that divides the city has become its recreational heart. The extreme monsoon climate—hot, wet summers and bitter Siberian winters—shapes every aspect of Seoul's urban life, from the flood walls along the Han to the heated ondol floors of Korean homes.