What is China's rooftop 'rain' cooling system? Can other countries adopt it too?

As record-breaking heatwaves grip parts of Asia, an unusual cooling technology from China has gone viral online.

Dubbed "rooftop rain" by social media users, the system appears to make it rain from the tops of apartment buildings, creating a curtain of mist that cools the surrounding area.

The videos have sparked curiosity around the world, with many wondering whether the technology is an alternative to air conditioning. While it may look like artificial rain, the system is actually based on a well-established scientific principle known as evaporative cooling.

What is China's rooftop 'rain' cooling system?

The rooftop 'rain' system consists of high-pressure misting nozzles installed along the roofs of residential buildings. When outdoor temperatures become extremely high, the nozzles release ultra-fine water droplets into the air.

Rather than soaking people below, the droplets are designed to evaporate before reaching the ground. As the water evaporates, it absorbs heat from the surrounding air, lowering the temperature around buildings, streets and public spaces.

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The system has attracted attention after being deployed in residential communities in Yuncheng, in China's Shanxi Province, where videos showing mist cascading from rooftops have spread widely across social media.

How does it cool the air?

The technology relies on evaporative cooling, the same process that helps cool the human body when sweat evaporates from the skin.

High-pressure pumps force water through specialised nozzles. These nozzles create microscopic droplets instead of large raindrops.

The droplets evaporate almost instantly in hot, dry air. During evaporation, heat energy is absorbed from the surrounding environment, reducing the ambient temperature.

According to reports from China, the system can lower surface temperatures by around 5°C to 8°C within minutes under suitable weather conditions.

Why is China using it?

Chinese cities have experienced increasingly frequent and intense heatwaves in recent years, with densely built urban areas becoming significantly hotter because of the urban heat island effect.

Concrete, asphalt and glass absorb heat during the day and release it slowly after sunset, causing cities to remain warmer than nearby rural areas.

The rooftop mist system is intended to reduce outdoor temperatures around residential buildings, improve comfort in shared public spaces, lower heat absorbed by building surfaces, and complement existing cooling measures during extreme heat events.

Rather than replacing conventional air conditioning, it is viewed as an additional strategy for making outdoor environments more bearable during heatwaves.

Is it the same as an outdoor air conditioner?

Long story short, no.

Although many social media posts describe it as an "outdoor air conditioner", the technology does not cool the air mechanically like conventional air conditioning systems.

Traditional air conditioners use compressors and refrigerants to remove heat from indoor spaces. The rooftop system simply accelerates the natural cooling effect created when water evaporates.

It also consumes considerably less energy than large-scale air conditioning because it primarily relies on pumps and misting equipment.

Does it work everywhere?

Not necessarily.

Evaporative cooling is most effective in hot, relatively dry conditions, where water can evaporate quickly.

Its performance is generally reduced in areas with high humidity because the air is already saturated with moisture, slowing the evaporation process. Researchers have long noted that evaporative cooling technologies are highly dependent on local climate conditions.

Are there any concerns?

While the technology has been praised as an innovative response to extreme heat, experts say several practical questions remain.

These include water consumption during prolonged heatwaves, maintenance of high-pressure nozzles, performance under different climatic conditions, long-term operating costs, and potential increases in local humidity.

Researchers also note that rooftop mist systems are intended to supplement, rather than replace, broader urban cooling measures such as green roofs, reflective building materials, increased tree cover and improved city planning.

Could other countries adopt similar systems?

Potentially, yes. Cities across the world are exploring ways to cope with rising temperatures driven by climate change.

Rooftop misting systems could become one option for cooling densely populated urban neighbourhoods, particularly in regions with hot and relatively dry summers.

However, experts caution that any large-scale deployment would need to consider local weather patterns, water availability and long-term sustainability before becoming part of wider climate adaptation strategies.