Analysis of fog water harvesting potential in the Atacama desert coastal mountains

At Alto Patache, a fog-monitoring station perched at 850 m elevation on Chile's coastal escarpment, standard fog collectors routinely gather 7-8 litres of water per square metre of mesh per day during the austral winter, enough to sustain a small community garden in one of the driest places on Earth. This research evaluated fog water harvesting potential across three sites in the Atacama Desert coastal mountains: Alto Patache, Paposo, and the Taltal Heights. Cylindrical standard fog collectors (1 m-squared Raschel mesh, 35% shade coefficient) were deployed at each site for 18 months (May 2021 to October 2022). Ancillary meteorological data, including wind speed and direction, relative humidity, temperature, and visibility, were recorded at 10-minute intervals by co-located automatic weather stations. Mean daily fog collection rates averaged 4.73 L/m2/day at Alto Patache, 3.21 L/m2/day at Paposo, and 3.94 L/m2/day at Taltal Heights. Fog frequency ranged from 164 to 213 days per year, peaking between June and September when the marine stratocumulus deck persists. Wind speed during fog events averaged 3.2-4.7 m/s from the southwest, optimal for mesh interception. A site-suitability index combining elevation, fog frequency, wind exposure, and accessibility ranked Alto Patache highest, followed by Taltal Heights. The analysis suggests that a 100 m-squared collector array at Alto Patache could supply approximately 170,000 litres annually, meeting the basic water needs of 30-40 people in an otherwise waterless landscape.

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Fog days/yr: Alto Patache vs Paposo vs Taltal HeightsClose ×

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SSI score (0-1): Alto Patache vs Paposo vs Taltal HeightsClose ×

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Introduction

Consider a fishing village on the Chilean coast where the nearest freshwater source is a desalination plant 40 km to the south and rainfall averages less than 2 mm per year. Now consider that the same village sits beneath a fog belt that delivers moisture equivalent to 100-200 mm annually to the mountain slopes directly behind it [1] . Fog water harvesting, the practice of intercepting wind-driven fog droplets on mesh screens, bridges this paradox by converting atmospheric moisture into a usable supply without energy-intensive desalination. The Atacama Desert coast is blanketed by a persistent marine stratocumulus layer, locally called camanchaca, generated by the cold Humboldt Current upwelling. When onshore winds push this cloud deck against the coastal escarpment at elevations between 400 and 1,200 m, fog droplets (5-40 micrometres diameter) deposit onto surfaces at rates that vary with mesh geometry, wind speed, and liquid water content [2] . The concept is not new: Schemenauer and Cereceda demonstrated its viability in the 1990s at El Tofo and Chungungo, where a 75-collector array supplied a village with 15,000 litres per day for several years before maintenance problems led to abandonment [3] . What has changed since those pioneering trials is the availability of low-cost weather sensors, higher-performance mesh materials, and GIS-based siting tools that can screen large areas for favourable topographic and meteorological conditions [4,5]. Yet systematic multisite comparisons of fog collection along the Atacama coastal mountains remain scarce. Most published data come from single-station records, making it difficult to generalise about how collection rates vary with latitude, elevation, and exposure [6] . This research addressed that gap by operating identical standard fog collectors at three sites spanning 250 km of coastline, recording meteorological covariates at high temporal resolution, and constructing a sitesuitability index to rank locations for operational deployment [7] .

Theoretical Background

Fog deposition on mesh collectors follows the physical principles of inertial impaction. As air carrying suspended droplets flows through a mesh, droplets with enough momentum deviate from the streamlines and collide with mesh filaments. The collection efficiency depends on the Stokes number, a dimensionless ratio of droplet inertia to air viscosity, which in turn varies with droplet diameter, wind speed, and filament diameter [8] . For typical Atacama fog conditions (droplet diameter 10-30 micrometres, wind speed 3-5 m/s, Raschel mesh filament 1 mm), collection efficiencies range from 20 to 40% of the liquid water content [2] . The shade coefficient of the mesh, defined as the fraction of area blocked by filaments, governs the trade-off between interception area and aerodynamic resistance; values near 35% represent an empirical optimum for Raschel polypropylene mesh [9] .

Study Area Description

Study Area Description

Material and Methods Material

Three cylindrical standard fog collectors (SFC) built to the Schemenauer-Cereceda design (1.0 m diameter, 1.0 m height, double-layer 35% shade Raschel mesh) were installed at each site in April 2021. Collection water drained through a 2 mm mesh pre-filter into calibrated tippingbucket rain gauges (0.2 mm resolution). Co-located Davis Vantage Pro2 automatic weather stations recorded temperature, relative humidity, wind speed and direction, barometric pressure, and solar radiation at 10-minute intervals. Visibility sensors (Biral VPF-710) measured atmospheric extinction coefficient as a proxy for fog liquid water content [10] . All instruments were solar-powered with data loggers transmitting via satellite modem.

Methods

Fog events were defined as continuous periods when visibility dropped below 1,000 m for at least 30 minutes. Daily collection rates (L/m2/day) were calculated by dividing total collected volume by the mesh cross-sectional area (1.0 m2) and the number of days. Seasonal and diurnal patterns were analysed by aggregating data into monthly means and hourly medians. A site-suitability index (SSI) was constructed as a weighted sum of five normalised variables: fog frequency (weight 0.30), mean daily yield (0.25), wind speed during fog events (0.20), elevation advantage (0.15), and road accessibility (0.10), with weights assigned by expert judgment [11] . Statistical comparisons between sites used Kruskal-Wallis tests with post-hoc Dunn tests at alpha = 0.05 in R 4.2.

Results

Results

Discussion

The 4.73 L/m2/day mean at Alto Patache exceeds the 3.0 L/m2/day threshold generally considered economically viable for community-scale fog harvesting [3] . Projected over a 100 m-squared collector array operating 365 days, this translates to roughly 170,000 litres per year, or about 470 litres per day. At a per-capita consumption of 12-15 litres per day (the minimum recommended by the WHO for drinking and cooking in emergency settings), such an array could serve 30-40 people [12] . The seasonal concentration of yield poses a storage challenge. Tanks sized to hold two months of supply would be needed to bridge the low-yield summer period. Hybrid systems that combine fog collection with small-scale solar desalination or atmospheric water generation could smooth the supply curve and improve reliability [13] . The cost of standard fog collectors (approximately USD 300 per m2 of mesh area, including structure and plumbing) compares favourably with trucked water (USD 5-15 per m3) and even with small reverse-osmosis units in remote locations [14] . The suitability index ranked Alto Patache first (SSI = 0.84) primarily because of its fog frequency and wind exposure advantages. Taltal Heights scored well on elevation and yield but was penalised by poor road access, which would increase installation and maintenance costs. Paposo, despite being the most accessible site, suffers from a topographic shadow that reduces fog interception [15] . These rankings should be treated as indicative; ground-truthing additional candidate sites with at least 6 months of SFC data is advisable before committing to large infrastructure investments [16] . [17,18] .

Conclusion

Conclusion

Acknowledgement

Acknowledgements Funding SourcesThis research was supported by internal funding from the Seoul Academy of Geographic Research.

Figures and tables from the paper

Parameter	Alto Patache	Paposo	Taltal Heights	p- value	Sig.	Best site
Fog days/yr	213	164	187	0.003	Yes	AP
Mean yield (L/m2/d)	4.73	3.21	3.94	<0.001	Yes	AP
Peak yield (L/m2/d)	7.24	5.18	6.43	0.008	Yes	AP
Wind speed in fog (m/s)	4.7	3.2	4.1	0.011	Yes	AP
SSI score (0-1)	0.84	0.58	0.72	—	—	AP

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Summary of fog collection performance at three Atacama

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Radar chart comparing normalised site performance variables for three Atacama fog collection stations

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Mean monthly fog water collection rates at Alto Patache over 18 months (dark bars indicate months with yield above 5 L/m2/day)

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