City skylines need an upgrade in the face of climate stress

By Mohamed Shaheen, Loughborough University

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  When structural engineers design a building, they aren’t just stacking floors; they are calculating how to win a complex battle against nature. Every building is built to withstand a specific “budget” of environmental stress – the weight of record snowfalls, the push of powerful winds and the expansion caused by summer heat. To do this, engineers use hazard maps and safety codes. These are essentially rulebooks based on decades of historical weather data. They include safety margins to ensure that even if a small part of a building fails, the entire structure won’t come crashing down like a house of cards. The problem is that these rulebooks are becoming obsolete. Most of our iconic high-rises were built in the 1970s and 80s – a world that was cooler, with more predictable tides and less violent storms. Today, that world no longer exists. Climate change acts as a threat multiplier, making the consequences of environmental stress on buildings much worse. It rarely knocks a building down on its own. Instead, it finds the tiny cracks, rusting support beams and ageing foundations and pushes them toward a breaking point. It raises the intensity of every load and strain a building must weather. To understand the challenge, I have been studying global hotspots where the environment is winning the battle against engineering. The 2021 collapse of Champlain Towers South in Miami, Florida, killed 98 people. While the 12-storey building had original design issues, decades of rising sea levels and salty coastal air acted as a catalyst, allowing saltwater to seep into the basement and garage. When salt reaches the steel rods inside concrete that provide structural strength (known as reinforcement), the metal rusts and expands. This creates massive internal pressure that cracks the concrete from the inside out — a process engineers call spalling. The lesson is clear: in a warming world, coastal basements are becoming corrosion chambers where minor maintenance gaps can escalate into catastrophic structural failure. While the Miami case affected a single building, the historic coastal city of Alexandria, Egypt, is more widely at risk. Recent research shows that building collapses there have jumped from one per year to nearly 40 per year in the past few years. Not only is the sea rising, the salt is liquefying the soft ground beneath the city foundations. As the water table rises, saltwater is pushed under the city, raising the groundwater level. This salty water doesn’t just rust the foundations of buildings; it changes the chemical and physical structure of soil. As a result, there are currently 7,000 buildings in Alexandria at high risk of collapse.

In Hong Kong during Super Typhoon Mangkhut in 2018, wind speeds hit a terrifying 180 miles per hour. When strong winds hit a wall of skyscrapers, they squeeze between the buildings and speed up — like water sprayed through a narrow garden hose. This pressure turned hundreds of offices into wind tunnels, causing glass windows to pop out of their frames and raining broken glass onto the streets below. With 82 deaths and 15,000 homes destroyed across the region, skyscrapers became “debris machines”, even if they didn’t fully collapse. Supercomputer simulations of Japan’s river systems show that in a world warmed by 2°C, floods of today’s “once in a century” magnitude could recur about every 45 years. With 4°C of warming, they could be every 23 years. These surges in water volume will expand flood zones into areas previously considered safe, potentially overflowing sea walls and flood defences. In a critical region like Osaka Bay, storm surges could rise by nearly 30%. In the US, a study of 370 million property records from 1945 to 2015 found over half of all structures are in hazard hotspots. Nearly half are facing multiple threats like earthquakes, floods, hurricanes and tornadoes. In the UK, climate-driven weather claims hit £573 million in 2023, a 36% rise from 2022. Annual flood damage to non-residential properties in the UK is also projected to nearly double from £2 billion today to £3.9 billion by the 2080s.

Maintenance is our best defence

Much of the world’s building stock is therefore entering its middle age under environmental conditions it was never designed to face. Instead of panicking or tearing everything down, the solution is to adapt and treat building maintenance as a form of climate resilience – not as an optional extra. Mid-life building upgrades can help protect our skylines for the next 50 years. Our hazard maps must look at future climate models — not just historical weather — to set new safety standards. Regular structural health monitoring is essential – by using sensors to track invisible stresses in foundations and frames before they become fatal, dangerous situations can be foreseen. Buildings can stay strong by focusing retrofits on the weakest and most vulnerable parts. This includes glass facades, the underground drainage, the foundation piles and corrosion protection. Climate change isn’t rewriting the laws of engineering, but it is rapidly eating away at our margins of safety. If we want our cities to remain standing, we must act now – before small, invisible stresses accumulate into irreversible failure.

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Mohamed Shaheen, Lecturer in Structural Engineering, Loughborough University This article is republished from The Conversation under a Creative Commons license. Read the original article.