Cities around the world are becoming hotbeds of growing heat stress, which is driven by a combination of global climate change and rapid urbanization. This phenomenon, known as urban heat island (UHI), causes built-up areas to experience significantly higher temperatures than their rural surroundings.

Why are cities warmer?

The main driver of urban heat is the surface characteristics of the landscape. Impervious materials, such as asphalt and concrete, absorb and retain heat, while the lack of vegetation limits natural cooling through shade and evaporation (evapotranspiration). The situation is exacerbated by anthropogenic heat – waste heat from transport, industry and especially air conditioning systems. Air conditioning systems create a vicious circle: although they cool interiors, they release heat into city streets, which can locally increase air temperatures by up to 1 to 3°C.

What will happen with global warming of 2°C?

Exceeding the critical 2°C limit of global warming set by the Paris Agreement will have dramatic consequences for urban populations:

• Faster warming of cities: A study of 104 medium-sized cities in the tropics and subtropics shows that in 81 % of them the average annual surface temperature will increase faster than in the surrounding rural landscape.
• Extreme increases in Asia: In some cities, particularly in India and China, surface temperatures are projected to rise by another 50 to 112 % beyond regional warming projections.
• Intensification of health risks: Extreme temperatures are considered one of the deadliest hazards in Europe. A single degree Celsius increase in temperature in a city during a heatwave can increase mortality by 2 to 5 %.
• Energy collapse: Demand for electricity for cooling can increase by 10% during extreme heat 20 to 30 %, which places a huge burden on energy networks and increases the risk of outages.

Who is most at risk?

Heat stress does not affect all residents equally. Among the most vulnerable groups These include older people (over 65 years old), children under 14 years old, pregnant women, people with chronic diseases, and low-income populations with limited access to green spaces or quality housing. Social isolation and living in poorly insulated apartments on the top floors are other risk factors.

Adaptation options: How to cool cities?

Cities are not helpless in the face of these developments. However, adaptation requires an integrated approach, which sources describe as three paths:

1. „"Green City": Expanding urban green spaces and planting trees. Trees can reduce ambient temperatures by 2 to 9°C thanks to shade and water evaporation.
2. „"Blue City": Using water bodies, fountains and ponds for natural cooling through evaporation.
3. „"White City": Using light, highly reflective materials for roofs and pavements (so-called high-albedo materials) that absorb up to 90 % less sunlight than dark asphalt.

New technologies, such as multimodal AI frameworks (e.g. GSM-UTCI), now allow planners to simulate different green transformation scenarios and accurately quantify their cooling effects before implementation. These tools confirm that targeted conversion of impervious surfaces to grass or tree canopy can reduce the perceived temperature (UTCI) by up to an average of 4.18 °C.

The future of cities beyond 2°C depends on how quickly urban planners and politicians can transform „concrete jungles“ into resilient and sustainable living environments. JRi&CO2AI