Dew in a Changing Climate: Why Atmospheric Water Harvesting Needs Citizen Scientists

Original Authors: Simon M. Berkowicz, Bert G. Heusinkveld

Original paper is accessible at: https://doi.org/10.3390/atmos17080724

The one water flux without a standard sensor

Meteorological stations measure temperature, precipitation, wind, humidity, and radiation with standard instruments. Dew is different. There is no defined sensor for dew.

How much dew forms depends on the surface as well as the atmosphere: sky view, atmospheric emissivity, water vapor content, wind speed, cloud cover, the height of the surface above the ground, and the material itself, whether rock, soil, leaves, glass, aluminum, or plastic film. Two collectors a few meters apart can record different values.

This matters more now than before. Dew exists in small quantities, so it should be particularly sensitive to climate change. Yet long-term meteorological stations are concentrated at airports, agricultural sites, research institutions, coastal areas, and cities. Large regions, such as the interiors of Australia, Canada, and Russia, have few or no stations.

This review asks two connected questions:

How is a changing climate likely to affect dew and atmospheric water harvesting, and how can we gather the long-term dew data needed to find out?

The authors’ answer to the second question is unusual for this field: enlist the public.

A field that has grown quickly

The review opens with evidence of how fast interest in AWH has grown. The authors summarize several bibliometric studies and add their own Web of Science search on dew water, dew harvesting, dew collection, and atmospheric water harvesting, which returned about 1,100 articles from 1981 to 2026.

One earlier analysis found that publications on dew and fog harvesting were below 10 per year before 2005 and rose to about 120 per year by 2020. The authors attribute this growth to pressure on freshwater resources, awareness of climate change, population growth, and urbanization.

The need is clear in the numbers the review cites:

• 2.1 billion people lack clean water, according to a 2025 WHO/UNICEF report.

• The number of people living in drylands rose from about 1.2 billion in 1990 to 2.3 billion in 2020.

• Drylands grew from 37.5% to 40.6% of Earth’s land area between 1961–1990 and 1991–2020.

• Worst-case projections suggest up to 5 billion people could live in drylands by 2100.

A drier atmosphere means less dew

The authors point to the “humidity paradox.” Warmer air can hold more water vapor, but over land its capacity to hold water rises faster than the moisture supply. The result is lower relative humidity, especially in growing cities. A “thirstier” atmosphere means fewer dew events and less condensation.

The studies the review collects mostly point in the same direction:

• Mediterranean basin: data from 142 stations project a 27% decline in dew yield during dry summer months by 2080.

• Jordan: 40-year simulations of annual dew yield show a decreasing trend.

• SW Madagascar: dew yields for 1991–2023 trend negative.

• Tibetan Plateau: field warming experiments showed artificial warming reduced dew formation.

• Global reanalysis: 34 years of data show regional dew yield trends of up to about ±10%.

There are exceptions. One study in Gujarat, India, found an increase in dew condensation for 2005–2021. Trends are regional, which is one reason the authors argue for denser observation.

This matters for practical applications too. In a semi-arid mountain region of Lebanon, an inclined 2 m² dew condenser could supply about 4.5 L per tree seedling during the hot, rainless months of June and July. Declining dew would weaken exactly this kind of use.

From passive panels to active machines

The review then surveys AWH approaches, focusing on dew and active systems and excluding fog and rain collection.

Passive radiative collectors cool a high-emissivity surface by radiating heat to the night sky, with no energy input. They are typically inclined at about 30° so water drains by gravity. Their output has a physical ceiling: about 0.5 L/m² per night is an upper bound. Notable examples include:

• The International Organization for Dew Utilization (OPUR) standard foil, about 400 µm thick, designed for strong radiative cooling

• The world’s largest dew collection system in India, totaling 850 m², which produced 6,545 L in 2007

• A cone-shaped radiation shield with a coated glass pane that cools up to 15 °C below ambient, allowing collection even during the day

• Bioinspired surfaces modeled on cactus spines, pitcher plants, and rice leaves

A practical limitation is that many droplets stay on the surface at sunrise and evaporate. Studies found that manual wiping once in the morning added about 50% more water, and automated wiping at 2:00, 4:00, and 6:00 AM increased collection by up to 70%.

Active condensers (AWGs) use either refrigeration-based cooling below the dew point or desiccants and sorbents such as silica gel, salts, MOFs, and COFs, followed by heat-driven release and condensation. The review notes newer approaches such as ultrasound-assisted desorption, which can release water from sorbents in minutes instead of hours. A study of 33 megacities found that RH exceeds 60% for more than half the year in these cities, suggesting a large potential market for AWGs.

Water quality is a recurring concern. Passive collectors are continuously exposed to particulate matter, chemicals, bacteria, and bird droppings, so the collected water needs filtration and disinfection. For commercial AWGs, the authors note that published water quality data remain limited.

The review also mentions several commercial products, including solar sorption panels, refrigeration-based generators, and hydropanels, with specifications taken from company websites. The authors present these for information only, not as recommendations.

The proposal: a citizen dew network

The central contribution of the paper is its proposal for citizen science (CS) dew monitoring.

Citizen science has a long history in environmental observation. Kyoto has records of peak cherry blossom dates going back to the year 812. The Christmas Bird Count in the US has run since 1900. Grape harvest dates in Beaune, France, form a record from 1354 to 2018. More recently, NASA’s Mountain Rain or Snow project has used about 1,700 volunteers reporting precipitation type through a phone app, which has improved precipitation modeling.

The authors argue that dew is an ideal candidate for this approach. It requires minimal instrumentation, is visible to anyone, and can serve as a sensitive local indicator of climate change. They say they know of only one existing citizen science project with a component on atmospheric water collection.

The proposed goals:

• Add quantitative data points that improve the resolution and accuracy of local, regional, and global dew models

• Use dew water for chemical analysis to map air pollution

• Test collector materials and designs in schools and universities

• Build water and environmental literacy from primary school to senior citizens

• Use teleconferencing to include participants anywhere, including low-income countries

What a citizen collector would look like

The authors call for a simple, inexpensive, lightweight, collapsible standard collector that can be sent by mail. They deliberately do not present their own design, to encourage independent ideas. They do give practical guidance:

• Surface: OPUR foil, PVC, corrugated PVC, or polycarbonate sheets, with about 3 cm of Styrofoam insulation underneath. Polypropylene channel plates are another option.

• Angle: 30° from horizontal.

• Placement: away from walls and trees, preferably facing west to delay early morning warming.

• Alternative: an inverted pyramid collector, which is unaffected by orientation.

For volunteers with no equipment at all, the review highlights a clever proxy: observing dew on car roofs at sunrise. Earlier work calibrated these observations against standard condensers and defined a four-category index with 20–30% uncertainty.

The suggested core dataset includes:

• Total dew collected per night (mL)

• Cloud cover in the early morning and at sunset (oktas)

• Number of dew nights per month and per year

• Histograms of dew volumes and of consecutive nights with and without dew

• Seasonal patterns and urban–rural comparisons

• Basic meteorological data where a school or institution has a weather station

Cities and green roofs

The review also highlights urban dew as an understudied area. Most dew research has been conducted in rural settings, yet roofs in cities can accumulate significant amounts of dew. One study estimated that rooftop dew and fog harvesting could supply 15–26% of the water needs of green roofs.

Dense, high-rise cities are less favorable for passive dew collection because of the urban heat island. That makes urban citizen dew data doubly valuable: it could improve modeling of the urban thermal radiation balance and reveal nocturnal hotspots.

Dew, art, and public engagement

The authors also argue that collaborations between artists and scientists can bring water scarcity to wider audiences. Examples include an architectural “Dew Catcher” cabin that integrates angled meshes into its structure, CAD-designed spiral dew collectors claimed to be several times more efficient than planar ones, and sculptures that use superhydrophobic surfaces to make dew visible.

Why this paper matters

This review contains no new experimental data, and its overview of active AWH technologies is brief. Its value lies elsewhere.

First, it collects the growing evidence that climate change is likely to reduce dew in many regions, which matters for anyone designing passive systems or estimating long-term yields.

Second, it identifies a real gap: dew is a water flux without a measuring standard or a dense observation network. The proposed citizen network would be inexpensive, scalable, and educational at the same time.

For the AWH community, this points to a practical opportunity. Universities, schools, and associations could build distributed dew monitoring networks using simple collectors and shared protocols. The result would be better climate data, better site assessment for harvesting systems, and a public that understands where water comes from.