•  Scientists are showing how basic nature and advanced deeptech can keep cities cool without electricity 

Saudi Arabia, like a growing proportion of the world, has a cooling problem. Air conditioning is estimated to consume half of the Kingdom's electricity demand — an unsustainable level for an urbanizing country, even one that is energy rich. 

In response, researchers at King Abdullah University of Science and Technology (KAUST) are conceiving new passive cooling solutions that use no electricity and instead manipulate water and light. These new technologies are cooling urban spaces for people to spend more time outdoors, greenhouses for higher crop yields, and buildings for lower energy costs.    

Rising temperatures are a global problem. 2025 saw the United Arab Emirates reach its highest recorded temperature ever in May at 51.6 C. Weeks later, thousands of people died in Europe because of heatwaves, with the United Kingdom having its hottest summer on record. And less rain and a record hot summer in Japan have contributed to the price of rice – the main staple of that nation's diet – doubling from last year.    

These unprecedented climate conditions are putting enormous stress on electricity grids all over the world, and it will only get worse. The International Energy Agency expects electricity consumption from air conditioning to increase 3-6 times by 2050. 

These energy demands will be hard to meet, posing risks not only to people's health, but also food security due to the inability to grow crops in controlled climates and the generation of sustainable energy, since solar, wind, and other renewable energy sources still depend on electronics that will break down in hotter temperatures.   

Using a mixture of nanotechnology and reflective materials, water evaporation and heat transfer, and advanced sensors and supercomputing, KAUST is developing a number of technologies for passive cooling that will allow cities and nations to grow sustainably. 

Pulling water from the air  

"Passive cooling moves heat without any external energy. It's the difference between turning on the air conditioning and jumping into a cool sea – the latter requires no electricity," explains KAUST Professor Qiaoqiang Gan. While not quite jumping to the sea, Gan has developed new nanotechnology that allows electronics to cool down by absorbing water from the surrounding air.    

Saudi Arabia is investing heavily in solar power. It averages more than 300 sunny days a year, making it one of the sunniest in the world and gives it a huge advantage in exploiting this renewable energy. However, constant exposure to sunlight at high temperatures creates a paradox, as it puts the same electronic devices generating solar power at risk of damage. 

Thus, solar panels need to be cooled, as otherwise they overheat, dropping their energy efficiency and lifespan. Just a rise of one degree can lower the performance of the solar cells constituting solar panels by approximately 0.5 percent.    

Gan's solution is to pull water from the air. His plastic nanomaterial absorbs moisture at night and releases it during the day. When affixed to solar cells, the released water keeps the solar cells cool while they operate under the Saudi sun. He has shown his material more than doubles the lifespan of the solar cells while significantly lowering the cost of electricity generation.  

Pulling water from the air is also the strategy used by Professor Kim Choon Ng to keep buildings cool sustainably. Ng is an expert in indirect evaporative cooling (IEC). IEC brings outdoor air into a building by passing it over a wet surface, causing water to evaporate. 

This process cools the air and raises its humidity. The air then flows through a heat exchanger, where it absorbs heat from the warmer air inside the building, thus cooling the indoors but without passing any of the outside humidity.    

Because the outdoor temperature is simply too high, in extremely hot places the passive heat transfer done by IEC alone cannot adequately mitigate supply air humidity and replace standard air conditioning, which relies on mechanical vapor compression (MVC). 

To overcome this, Ng has developed IEC–MVC hybrids that match the performance of MVC units while significantly reducing energy use. Indeed, Ng has shown that retrofitting buildings in Saudi Arabia with IEC-MVC hybrids can reduce annual electricity consumption by 33 percent. 

There is a catch, however. Because IEC depends on a wet surface, it needs water. Consequently, while IEC-MVC hybrids reduce electricity demand, their innate dependency on water could cause other sustainability issues in regions like the Middle East, where water production and transportation are costly. 

MVC by design produces water, which is why people walking under a building with air conditioners outside may feel drops on their head even when there is no cloud in the sky. In IEC-MVC hybrids, this water is collected and used to maintain the wet surface. 

Ng has shown that IEC-MVC hybrids can eliminate any need for additional water in humid cities like Jeddah, further demonstrating the viability of this approach in hot climates that are undergoing major urbanization.  

Reflecting light away   

Another way to keep cool is to bend light. The sun not only keeps the days bright, it makes them hot. For example, solar panels only convert around 20 percent of the light they absorb into energy, with the rest causing heat. The same is true for streetlights.    

Streetlights are directed downward to illuminate the ground. Another nanotechnology by Gan turns streetlights on their head by directing heat to the sky. In this case, infrared light, which causes heat and is invisible, passes through the nanotechnology and continues unabated upward and away from the electronics. 

In contrast, the nanotechnology reflects visible light back to the ground. The result is the same illumination, but a device almost five degrees cooler and a lifespan almost 25 percent longer at no extra cost.    

Bending light with Gan's technology is also a solution to growing food. Plants depend on sunlight to grow, but not all sunlight, and the rest, like with electronics, mostly creates heat. Due to its climate, Saudi Arabia depends heavily on food imports, but the Kingdom aims to reduce this foreign dependency through greenhouses, which must be kept at fixed temperatures for their crops. 

Consequently, greenhouses are equipped with energy-intensive fans and air conditioners that consume lots of water. To mitigate this need, Gan has developed another nanotechnology. Coating greenhouses with it blocks the light not used by plants to grow from entering the greenhouse, in effect acting like a doorman that only lets good light in and keeps bad light out. 

By reflecting the unwanted light out, Gan's technology has helped reduce soil temperatures dramatically, expanded the growing season in Saudi by nearly 50 percent, and tripled the yield of some crops.  

Cooler cities  

The above sustainable strategies are helpful for improving individual units, akin to someone replacing their gasoline automobile with an electric vehicle, but unless widely adopted, the impact remains limited. To work on a much larger scale, KAUST scientists are also looking at not just the design of individual buildings but of whole cities.    

The urban heat island effect is a serious threat to human health. These islands are the result of urban design, including dense buildings, paved surfaces, and limited greenery. The result is urban areas absorbing and retaining more heat, making them several degrees warmer than the nearby countryside. This intensified heat raises cooling demands, worsens air quality, and increases health risks during heatwaves. 

Proper city planning is therefore essential for the Kingdom to achieve its ambitious goals in growth. This planning depends on data, and for this data, ministries and other national bodies have turned to KAUST.   

"We are constructing digital twins of cities and using sophisticated mathematical models to predict best practices for adding greenery, selecting construction materials, and other measures to keep urban temperatures low while minimizing energy and water consumption," said KAUST Professor Sami G. Al-Ghamdi.   

Digital twins are virtual replicas of cities that let scientists analyze the urban effects of changing a massive construction project, such as the roof of a building or numbers of trees in a neighborhood, before a single shovel hits the ground. Using sophisticated sensors, Al-Ghamdi is collecting climate data for his computational models that are being run on the KAUST supercomputer, the fastest supercomputer at a university in the Middle East. 

These models are simulating the effects of different strategies on city livability and informing urban design for the next 100 years, including how to create shade, construct parks, and design buildings.   

Al-Ghamdi expects research like his will make cities anywhere in the world accommodating to pedestrians, cyclists, and public transportation, as well as protect biodiversity and infrastructure.    

"Parks, reflective materials, shading, all of these can make cities more livable even if overall temperatures rise. But we cannot just build in places where people want to live. We need good science and good data to build sustainably," he said. 

Another contributor to cooling urban centers is the startup Sadeem, a deep-tech company founded by KAUST graduates. Its combination of satellite technologies, internet of things technology, and AI models is allowing scientists and policymakers to predict and analyze urban heat islands as well as the effects of mitigation strategies.    

Sadeem products are already being used in seven countries, but its CEO, Mustafa Mousa, said that the company's success and its provision of services across the Kingdom would never have manifested without KAUST support.   

"KAUST has been essential to us. They have allowed us to prototype and test our technologies on their campus. I am certain we would have gone outside the Kingdom to create our company had KAUST not been available."   

With global temperatures rising, more and more countries see cooling as necessary for livable cities, but simply building more air conditioners is not sustainable. KAUST solutions range from the natural, by taking water from the sky or bending sunlight, to the digital, by using the most advanced sensors and computational technologies. 

These innovations are enabling the Kingdom to grow and thrive in a warmer world and also place it at the forefront of sustainable cooling.