How morning fog could be vital water source in world’s driest desert

SANTIAGO, Chile — As cities worldwide grapple with water shortages, researchers in northern Chile are turning their attention skyward, not for rain, but for fog. In Alto Hospicio, a rapidly growing city in the Atacama Desert where the annual rainfall barely registers on a measuring stick, this could be a potential solution to urban water scarcity. Scientists are testing whether that daily fog that rolls in from the Pacific Ocean could help solve the growing water crisis in one of Earth’s driest places.

Rising like a mirage from the desert plateau, Alto Hospicio faces a critical challenge shared by many rapidly growing urban areas in arid regions: its main water source is running dry. According to new research published in Frontiers in Environmental Science, the city’s 113,000 residents currently rely on underground aquifers, rock layers containing water-filled pore spaces, that were last recharged with rainfall between 17,000 and 10,000 years ago. These aquifers are essentially mining prehistoric water that cannot be replenished in our lifetime.

Nature may offer an unexpected solution. The coastal fog known locally as “camanchaca,” an Aymara word meaning “darkness,” regularly blankets the region. This fog forms when warm air masses above the cold Pacific Ocean create low-lying clouds that the wind pushes toward the continent. A unique combination of geographic features makes this fog remarkably reliable: the cold Humboldt ocean current, high-pressure systems that prevent rainfall, and the steep coastal mountain range that traps moisture-laden air.

“This research represents a notable shift in the perception of fog water use—from a rural, rather small-scale solution to a practical water resource for cities,” says co-study author Virginia Carter Gamberini, an assistant professor at Universidad Mayor, in a statement. “Our findings demonstrate that fog can serve as a complementary urban water supply in drylands where climate change exacerbates water shortages.”

The fog collection system is remarkably straightforward: large mesh panels are suspended between posts and positioned vertically facing the prevailing winds. As fog passes through the mesh, tiny water droplets collide and combine, eventually growing large enough to run down into collection gutters below. The collected water then flows into storage tanks. It’s a passive system requiring no external energy, particularly important for informal settlements with limited infrastructure.

Alto Hospicio’s water challenges mirror those facing many rapidly growing desert cities. The municipality emerged as a satellite center of the regional capital Iquique, initially housing populations who couldn’t afford coastal city prices. Over decades, government housing policies and urban migration swelled the population, but infrastructure development couldn’t keep pace. Today, water access remains deeply unequal.

While 99.94% of Chile’s urban residents officially have access to potable water, the reality in Alto Hospicio’s informal settlements tells a different story. Of the estimated 10,000 people living in these areas, only 1.6% are connected to water distribution networks. Most depend on water truck deliveries, an expensive and unreliable system that costs the municipality an estimated annual cost of over $23,000.

By combining real-world measurements with sophisticated modeling, the researchers identified prime fog harvesting zones in the northeast and southeast areas surrounding Alto Hospicio. These sweet spots, located at elevations between 700 and 1,000 meters above sea level, could collect between 0.2 and 5 liters of water per square meter daily. During peak season in August and September 2024, collection rates reached up to 10 liters per square meter per day.

The timing couldn’t be better. Alto Hospicio is experiencing rapid growth, with its population projected to reach 178,800 by 2035. The city also faces significant social challenges. In the broader Tarapacá region, about 24% of residents experience multidimensional poverty, a measure that considers factors like access to education, healthcare, housing quality, and basic services. The average monthly income in Alto Hospicio ($560) falls well below both the national average ($760) and neighboring Iquique ($877).

The study suggests that collected fog water could serve multiple purposes beyond basic consumption. The city’s public green spaces, currently covering 30 hectares, require more than 100,000 liters of potable water for irrigation. Fog water could meet this demand while freeing up treated water for drinking. Additionally, the water could support hydroponic agriculture, a soil-free growing method that uses up to 90% less water than traditional farming. Research suggests a single square meter of a hydroponic system could yield 15 to 20 kilograms of leafy green vegetables monthly, potentially improving food security in a region where fresh produce is typically imported at high cost.

“Key prerequisites include fog density, suitable wind patterns, and well-oriented elevated landforms,” explains study co-author Nathalie Verbrugghe, a researcher at Université libre de Bruxelles. “Additionally, since fog is seasonal in many regions, this variability should be considered.”

The concept has already proven successful in smaller settings. Since the 1980s, various fog collection projects have supported rural communities in Chile, Peru, Morocco, and other arid regions. What makes the Alto Hospicio study groundbreaking is its urban focus and potential scale.

The researchers calculated that a fog collection system using about 17,000 square meters of mesh, roughly equivalent to two and a half soccer fields, could theoretically meet the weekly water demand (300,000 liters) for urban settlements. A smaller installation of 110 square meters could supply the annual irrigation needs for the city’s green spaces. However, significant infrastructure investments would be needed, including large storage systems, piping networks, and distribution systems to bridge the seasonal availability gap.

From an environmental perspective, fog harvesting could reduce pressure on the region’s dwindling aquifers while providing a sustainable alternative to energy-intensive desalination. It could also support urban greening initiatives crucial for combating the heat island effect, where cities are significantly warmer than surrounding areas.

Beyond Alto Hospicio, this research could be helpful for arid cities worldwide. As climate change and rapid urbanization strain conventional water sources, innovative solutions become increasingly crucial. The study demonstrates that sometimes sustainable alternatives can be found in traditional knowledge. The region’s indigenous peoples have long recognized fog as a water source, combined with modern technology and urban planning.

“We hope to encourage policymakers to integrate this renewable source into national water strategies,” adds Carter. “This could enhance urban resilience to climate change and rapid urbanization while improving access to clean water.”

While fog collection alone won’t solve Alto Hospicio’s water challenges, the research suggests it could form an important part of a diversified water management strategy. For arid cities facing similar challenges, partial solutions to water scarcity could be found by better utilizing the natural phenomena already present in their environments. For Alto Hospicio, that solution happens to be drifting by in the morning fog.