HEAT BUBBLE: The Urban Climate of the Walled City

Stepping onto the bustling campus of Pamantasan ng Lungsod ng Maynila (PLM), one can’t help but notice the heat. Students fanning themselves with notebooks, the glare bouncing off concrete walls, and the sweltering afternoon air have become a quintessential part of campus life.

"ANG INIT!"

"PAPASOK NA NAMAN TAYO SA IMPYERNO!"

Phrases that echo across PLM as students make their way across campus. Known as the “Premier People University of Manila,” PLM sits at the heart of Intramuros—a historic district that attracts both locals and tourists eager to experience the rich cultural heritage of Manila. But the same heritage and location that make PLM special also play a part in the stifling heat that has become a signature discomfort for its students and staff. It’s also a melting pot of environmental factors—both natural and man-made—that turn up the temperature. From its geographic quirks to the remnants of its colonial past, PLM’s unique setting tells a story of heat, humidity, and history intertwined.

𝗚𝗘𝗢𝗚𝗥𝗔𝗣𝗛𝗜𝗖 𝗟𝗢𝗖𝗔𝗧𝗜𝗢𝗡

Intramuros is cradled between two iconic bodies of water—the Pasig River and Manila Bay. While these waterways are integral to the city’s identity, they come with a steamy consequence: humidity. The rivers release water vapor into the air, intensifying the heat index and making the temperature feel higher than it actually is.

What’s more into this is, water has a knack for holding onto heat. In NASA’ Understanding Climate, explained that the solar heat is absorbed by the bodies of water during the day, and is released at night. This means that throughout the day, the Pasig River and Manila Bay soak up the sun’s energy and slowly release it overnight, blanketing the area in lingering warmth. For PLM students, this means even evenings offer little reprieve from the oppressive heat.

To make matters worse, their interaction with Intramuros' dense urban layout disrupts airflow, trapping warm, humid air. Combined with the urban heat island effect, the heat gets trapped, hanging over the campus like an invisible cloud of discomfort.

𝗨𝗥𝗕𝗔𝗡 𝗗𝗘𝗦𝗜𝗚𝗡 𝗔𝗡𝗗 𝗟𝗔𝗡𝗗𝗦𝗖𝗔𝗣𝗘

The walled city was designed to protect its inhabitants, standing as steadfast guardians against invasions and the tests of time. Yet, in an ironic twist, these very walls that once offered protection now intensify a relentless modern challenge: the unrelenting heat. Crafted during the Spanish colonial era, Intramuros’ urban design prioritized fortification over comfort, leaving its inhabitants to grapple with the unintended consequences of history’s architectural legacy.

In Glenn Orbon’s 2014 study, Walled City in the Tropics, he noted how the traditional “bahay na bato” architecture, with its narrow streets and interconnected houses, left minimal room for trees and vegetation—natural cooling agents in urban settings. The limited green spaces in Intramuros are often confined to institutional areas like church grounds and government plazas, offering shade but falling short of counteracting the overall urban heat effect.

Trees and vegetation play a vital role in urban cooling by absorbing sunlight and releasing water vapor through transpiration. Without sufficient greenery, Intramuros is dominated by heat-absorbing materials like concrete and asphalt. These hard surfaces act as thermal sponges, soaking up heat during the day and radiating it back at night.

This combination of historical design and modern urbanization has turned Intramuros into a textbook example of the Urban Heat Island (UHI) effect. In this phenomenon, built-up areas experience significantly higher temperatures than their rural counterparts due to the abundance of heat-absorbing materials and the absence of natural cooling elements. For PLM students, this means navigating a campus where every concrete surface and tightly packed building traps and amplifies the heat.

The result is a landscape that may be picturesque but is far from practical in Manila’s tropical climate. Intramuros’ streets and courtyards, designed centuries ago, are now hotspots—both culturally and thermally.

𝗦𝗧𝗥𝗘𝗘𝗧 𝗖𝗔𝗡𝗬𝗢𝗡 𝗘𝗙𝗙𝗘𝗖𝗧

The "street canyon effect" is a phenomenon that turns the narrow corridors of Intramuros into heat traps. At first glance, the tightly packed urban fabric might seem like a clever design to combat Manila's tropical heat—after all, these narrow streets limit direct sunlight from hitting the ground, providing shade for pedestrians. However, this same design unintentionally creates a host of problems that amplify the heat felt in the Walled City, particularly within the Pamantasan.

As Orbon’s study highlights, street canyons form when buildings line both sides of a narrow road, resembling natural canyons carved into the earth.These "canyons" significantly impact how sunlight, heat, and airflow interact within the space. In Intramuros, the tall, densely packed buildings act as barriers that block sunlight during certain parts of the day, reducing solar heating of the ground. While this shading effect might seem advantageous, it also prevents effective airflow, trapping heat and reducing natural ventilation.

On calm days, when the winds fail to penetrate these corridors, warm air lingers and accumulates between the walls. Without a consistent breeze to disperse it, the heat becomes concentrated, creating stifling conditions that can feel several degrees hotter than in open areas. This trapped heat is further compounded by the materials that make up Intramuros' streets and buildings—concrete, asphalt, and stone, which absorb solar radiation during the day while also releasing it slowly at night. The result is a microclimate that remains warm even after the sun sets.

Ironically, the very design intended to shield the streets from direct sunlight also becomes a key contributor to the sweltering conditions. The lack of ventilation in these shaded alleys creates a space where heat not only persists but thrives, especially during peak hours when activity within Intramuros is at its highest.

𝗨𝗥𝗕𝗔𝗡𝗜𝗭𝗔𝗧𝗜𝗢𝗡

Nestled in the bustling core of Manila, as part of Intramuros, the historic yet densely urbanized district, PLM is a subject to the UHI phenomenon—an invisible but impactful force that traps more heat in cities compared to their rural counterparts.

Urbanization has transformed Intramuros from a fortress of history into a lively hub teeming with students, tourists, and residents. However, this transformation comes with a price. The heavy concentration of concrete, asphalt, and stone, materials notorious for absorbing and retaining heat, ensures that the area radiates warmth long after the sun has set. Unlike rural landscapes that boast greenery and open spaces, urbanized areas like Intramuros lack natural cooling systems, leaving heat to build up unchecked.

For PLM, urbanization’s effects are felt on multiple fronts. The relentless flow of vehicles in and around Intramuros is a major contributor. Traffic congestion generates significant heat from car engines and exhaust, which lingers in the narrow streets, compounding the already high temperatures. These roadways, hemmed in by dense infrastructure, trap the heat, turning the district into a simmering cauldron.

𝗕𝗲𝘆𝗼𝗻𝗱 𝘁𝗵𝗲 𝗪𝗮𝗹𝗹𝘀..

As the sun sets over the towering walls of Intramuros, the heat lingers, a testament to the historic district's layered identity. At PLM, the daily challenge of enduring this heat urban bubble has become an inseparable part of campus life. The echoes of "Ang init!" and "Parang impyerno!" are more than complaints—they are reflections of a community adapting to an environment shaped by history, geography, and modernization.

While the Walled City stands as a monument to resilience and heritage, it also calls for innovation and solutions to address its pressing urban climate challenges. Just as Intramuros has weathered the trials of centuries, perhaps it can also rise above the relentless heat, transforming discomfort into an opportunity for sustainable growth and revitalization. Perhaps now, it’s time for those within to take up the mantle of protection—not just for the Walled City’s legacy, but for the people who walk its historic streets.

REFERENCES

Air & Water | Understanding Climate – Ocean Surface Topography from Space. (2020). Ocean Surface Topography from Space. https://sealevel.jpl.nasa.gov/ocean-observation/understanding-climate/air-and-water/

https://www.researchgate.net/publication/266673283_Walled_City_in_the_Tropics_An_Analysis_of_the_Urban_Fabric_and_Tropical_Design_Considerations_of_Intramuros