Camilo del Río

In the coastal Mediterranean climate–type forests of Chile, precipitation is lower than evapotranspiration, resulting in an apparent water imbalance that contradicts the level of forest greening. As precipitation alone does not meet evapotranspiration requirements, fog may act as a complementary water input that helps offset this apparent imbalance. This input appears to come from fog intercepted by the forest, generated by marine stratocumulus (Sc) clouds trapped by ocean‐facing mountain slopes. Because the Sc cloud has a well‐defined vertical liquid structure and the forest is distributed along a steep slope that intersects it, the influence of fog varies with elevation. Likewise, as fog interacts with a heterogeneous topography that modifies the prevailing wind direction, its influence is strongly controlled by slope orientation. To address this complexity, we combine surface observations of fog‐water collection, tree fog dripping, satellite information and a fog‐harvesting model to analyse the water codependency of a coastal forest on the vertical and horizontal distribution of marine fog. Fog occurs with a frequency of 15% throughout the year, peaking in March (12 mm of fog‐drip collection) and September (16 mm). On the vertical scale, tree fog dripping increases linearly with elevation, as does fog influx ( R = 0.6), and the progressive increase in epiphytic lichens (Usnea sp. and Heterodermia sp.) along the same gradient reflects the enhanced influence of fog interception. On the horizontal scale, forest NDVI reaches its highest values (0.7) in areas where the model indicates the greatest collection. Considering modelled fog influx and tree fog dripping, we estimate a forest passive collection efficiency of ~12%. Finally, using a simplified and idealised water balance for fog‐facing slopes, we estimate that fog collection contributes 27% (127 mm year ⁻¹ ) of the annual water inputs, supporting the role of fog as a complement to precipitation in the forest water balance.

The Atacama Desert hosts a unique ecosystem formed by the sand-dwelling Tillandsia landbeckii, which extends over hundreds of square kilometers. This vegetation relies primarily on fog as its main water source; however, aeolian sand also plays a crucial role in the long-term persistence of both the species and the overall plant community. The terrain is sloped and exposed to the prevailing wind direction. Tillandsia forms regular banding patterns oriented orthogonally to these landscape features. In this study, we aim to elucidate the abiotic–biotic interactions between sand properties and vegetation characteristics through a comparative approach. Three populations – Caldera, Oyarbide and Arica –, each spanning several square kilometers in the southern, central, and northern regions of the Chilean Atacama Desert, were selected to compare wind regimes, terrain structure, sand and substrate properties, and vegetation structure in order to identify common principles that maintain vegetation integrity. Data were collected from six climate stations, 1,246 substrate samples, population genomic data from 718 individuals, as well as satellite imagery and digital terrain models. Our findings demonstrate that regional wind systems transport sand from distant source areas, while near the ground, Tillandsia vegetation reduces wind velocity and traps sand, leading to the formation of moderately sorted sandy substrates that are similar across all three populations. Sites lacking or containing dead Tillandsia individuals often differ significantly in substrate characteristics. Genetic analyses indicate that Tillandsia populations exhibit strong spatial structure albeit recruiting high genetic diversity and an excess of heterozygosity, reflecting adaptation to the dynamic environmental conditions. We conclude that sand represents an essential component of this ecosystem, while Tillandsia, as the dominant biotic factor, actively shapes and maintains this distinctive desert environment.

The Atacama Desert hosts a unique ecosystem formed by the sand-dwelling Tillandsia landbeckii, which extends over hundreds of square kilometers. This vegetation relies primarily on fog as its main water source; however, aeolian sand also plays a crucial role in the long-term persistence of both the species and the overall plant community. The terrain is sloped and exposed to the prevailing wind direction. Tillandsia forms regular banding patterns oriented orthogonally to these landscape features. In this study, we aim to elucidate the abiotic–biotic interactions between sand properties and vegetation characteristics through a comparative approach. Three populations – Caldera, Oyarbide and Arica –, each spanning several square kilometers in the southern, central, and northern regions of the Chilean Atacama Desert, were selected to compare wind regimes, terrain structure, sand and substrate properties, and vegetation structure in order to identify common principles that maintain vegetation integrity. Data were collected from six climate stations, 1,246 substrate samples, population genomic data from 718 individuals, as well as satellite imagery and digital terrain models. Our findings demonstrate that regional wind systems transport sand from distant source areas, while near the ground, Tillandsia vegetation reduces wind velocity and traps sand, leading to the formation of moderately sorted sandy substrates that are similar across all three populations. Sites lacking or containing dead Tillandsia individuals often differ significantly in substrate characteristics. Genetic analyses indicate that Tillandsia populations exhibit strong spatial structure albeit recruiting high genetic diversity and an excess of heterozygosity, reflecting adaptation to the dynamic environmental conditions. We conclude that sand represents an essential component of this ecosystem, while Tillandsia, as the dominant biotic factor, actively shapes and maintains this distinctive desert environment.

The Atacama Desert hosts a unique ecosystem formed by the sand-dwelling Tillandsia landbeckii, which extends over hundreds of square kilometers. This vegetation relies primarily on fog as its main water source; however, aeolian sand also plays a crucial role in the long-term persistence of both the species and the overall plant community. The terrain is sloped and exposed to the prevailing wind direction. Tillandsia forms regular banding patterns oriented orthogonally to these landscape features. In this study, we aim to elucidate the abiotic–biotic interactions between sand properties and vegetation characteristics through a comparative approach. Three populations – Caldera, Oyarbide and Arica –, each spanning several square kilometers in the southern, central, and northern regions of the Chilean Atacama Desert, were selected to compare wind regimes, terrain structure, sand and substrate properties, and vegetation structure in order to identify common principles that maintain vegetation integrity. Data were collected from six climate stations, 1,246 substrate samples, population genomic data from 718 individuals, as well as satellite imagery and digital terrain models. Our findings demonstrate that regional wind systems transport sand from distant source areas, while near the ground, Tillandsia vegetation reduces wind velocity and traps sand, leading to the formation of moderately sorted sandy substrates that are similar across all three populations. Sites lacking or containing dead Tillandsia individuals often differ significantly in substrate characteristics. Genetic analyses indicate that Tillandsia populations exhibit strong spatial structure albeit recruiting high genetic diversity and an excess of heterozygosity, reflecting adaptation to the dynamic environmental conditions. We conclude that sand represents an essential component of this ecosystem, while Tillandsia, as the dominant biotic factor, actively shapes and maintains this distinctive desert environment.

Water insecurity is a growing challenge in arid regions, especially in rural settlements with limited access to conventional water sources. Along the Atacama Desert coast, fog represents a potential complementary resource, although its feasibility depends on environmental, technical, and social conditions. This study assesses whether fog harvesting could improve water security in Chanavaya (20°54′ S, 70°8′ W), northern Chile. We combined an analysis of the water governance framework, modelling of fog-harvesting potential using the Advective Fog Model for Arid and Semi-arid Regions under Climate Change (AMARU), and a survey of community perceptions. Results show that many residents have limited water access and depend heavily on tanker-truck deliveries, often below WHO-recommended service levels. The modelling reveals strong seasonality, with the highest collection potential between May and November. A system with 1,800 m² of netting could substantially increase water availability and meet current and intermediate demand during several months of the year. Survey responses indicate high awareness of fog, favourable attitudes toward harvested fog water, and willingness to use it as a complementary supply. Fog harvesting could therefore strengthen water security in coastal desert settlements, but successful implementation also requires adequate governance, infrastructure, maintenance, and sustained community acceptance.

The Atacama Desert hosts a unique ecosystem formed by the sand-dwelling Tillandsia landbeckii, which extends over hundreds of square kilometers. This vegetation relies primarily on fog as its main water source; however, aeolian sand also plays a crucial role in the long-term persistence of both the species and the overall plant community. The terrain is sloped and exposed to the prevailing wind direction. Tillandsia forms regular banding patterns oriented orthogonally to these landscape features. In this study, we aim to elucidate the abiotic–biotic interactions between sand properties and vegetation characteristics through a comparative approach. Three populations – Caldera, Oyarbide and Arica –, each spanning several square kilometers in the southern, central, and northern regions of the Chilean Atacama Desert, were selected to compare wind regimes, terrain structure, sand and substrate properties, and vegetation structure in order to identify common principles that maintain vegetation integrity. Data were collected from six climate stations, 1,246 substrate samples, population genomic data from 718 individuals, as well as satellite imagery and digital terrain models. Our findings demonstrate that regional wind systems transport sand from distant source areas, while near the ground, Tillandsia vegetation reduces wind velocity and traps sand, leading to the formation of moderately sorted sandy substrates that are similar across all three populations. Sites lacking or containing dead Tillandsia individuals often differ significantly in substrate characteristics. Genetic analyses indicate that Tillandsia populations exhibit strong spatial structure albeit recruiting high genetic diversity and an excess of heterozygosity, reflecting adaptation to the dynamic environmental conditions. We conclude that sand represents an essential component of this ecosystem, while Tillandsia, as the dominant biotic factor, actively shapes and maintains this distinctive desert environment.

Marine fog represents a critical but variable water resource in hyperarid coastal regions, yet its chemical variability at the event scale and meteorological controls remain poorly characterized. This study provides an event-based characterization of fog water chemistry at Alto Patache (~20°S), Atacama Desert, Chile, based on 28 fog events sampled between 2022 and 2024 using a Caltech Active Strand Cloudwater Collector (CASCC) with meteorological monitoring. Seven chemical parameters were measured in situ (alkalinity, hardness, pH, phosphate, ammonium, nitrite, and nitrate), and k-means clustering identified three chemically distinct regimes: dilute (Cluster 0, n = 19), enriched (Cluster 1, n = 6), and buffered (Cluster 2, n = 3), validated by permutation-based analysis (PERMANOVA, p < 0.001). Fog events with higher water yields are associated with better water quality: fog water volume showed the strongest relationship with solute concentration, consistent with a dilution mechanism, with high-yield events showing substantially lower ionic concentrations. Event duration and wind speed exhibited secondary complementary patterns, while wind direction had no clear relationship with fog chemistry. These findings indicate that fog water quality is closely linked to event-scale hydrological processes, with direct implications for fog harvesting management, water quality assessment, and understanding biogeochemical subsidies in fog-dependent ecosystems.

The Atacama Desert hosts a unique ecosystem formed by the sand-dwelling Tillandsia landbeckii, which extends over hundreds of square kilometers. This vegetation relies primarily on fog as its main water source; however, aeolian sand also plays a crucial role in the long-term persistence of both the species and the overall plant community. The terrain is sloped and exposed to the prevailing wind direction. Tillandsia forms regular banding patterns oriented orthogonally to these landscape features. In this study, we aim to elucidate the abiotic–biotic interactions between sand properties and vegetation characteristics through a comparative approach. Three populations – Caldera, Oyarbide and Arica –, each spanning several square kilometers in the southern, central, and northern regions of the Chilean Atacama Desert, were selected to compare wind regimes, terrain structure, sand and substrate properties, and vegetation structure in order to identify common principles that maintain vegetation integrity. Data were collected from six climate stations, 1,246 substrate samples, population genomic data from 718 individuals, as well as satellite imagery and digital terrain models. Our findings demonstrate that regional wind systems transport sand from distant source areas, while near the ground, Tillandsia vegetation reduces wind velocity and traps sand, leading to the formation of moderately sorted sandy substrates that are similar across all three populations. Sites lacking or containing dead Tillandsia individuals often differ significantly in substrate characteristics. Genetic analyses indicate that Tillandsia populations exhibit strong spatial structure albeit recruiting high genetic diversity and an excess of heterozygosity, reflecting adaptation to the dynamic environmental conditions. We conclude that sand represents an essential component of this ecosystem, while Tillandsia, as the dominant biotic factor, actively shapes and maintains this distinctive desert environment.

In the coastal Atacama Desert, fog and dew represent the main atmospheric water inputs to the surface water balance in a context of near-total absence of precipitation. Both processes originate from the advection of the marine boundary layer (MBL) over the coastal topography, strongly influencing the spatial distribution of xeric, highly adapted ecosystems. Despite advances in understanding MBL advection under fog conditions, the physical differentiation between fog and dew remains unclear due to instrumental limitations, hindering their independent quantification and the assessment of their hydrological role. This study focuses on the thermodynamic characterization of the MBL under fog and dew events in the coastal Atacama Desert and is structured around three main objectives: (1) reclassification of atmospheric water harvesting events, (2) analysis of MBL stability, and (3) assessment of moisture tendency evolution. The analysis is based on a topographic transect of meteorological stations facing the ocean, distributed between 48 and 1354 m a.s.l., using 10-minute observations collected during 2024. Event reclassification integrates visibility measurements and the Fog Low Cloud (FLC) product from the GOES satellite, enabling discrimination between fog and dew beyond the signal provided by standard fog and dew collectors (SFC and SDC). Preliminary results indicate that standard collectors fail to adequately distinguish fog from dew events, as the inclusion of visibility and satellite information increases the annual proportion of dew events from 0.5% to 3.4%, while fog events remain close to 3.4%. Analysis of vertical profiles of potential temperature (θ) and specific humidity (q) shows that fog events are associated with a thermally and moisture well-mixed MBL, whereas dew formation occurs under a stratified (stable) MBL. In particular, the vertical gradient of θ reveals distinct stability thresholds differentiating fog (∂θ/∂z < 0.0020 K m⁻¹) from dew (0.0020 K m⁻¹ < ∂θ/∂z < 0.0031 K m⁻¹) events, while vertical profiles of q do not show significant differences between event types. Finally, the analysis of moisture tendency (∂q/∂t) reveals small but significant differences between fog and dew events, with sharper moisture decreases during dew conditions, indicating stronger atmosphere–surface water exchange at dawn. This study contributes to disentangling the atmospheric processes controlling fog and dew occurrence in the driest place on Earth.

The northern and central coast of Chile exhibits a pronounced aridity gradient extending over 1,000 km, from the hyperarid Atacama Desert (~18°S) to the Mediterranean shrublands of central Chile (~34°S). This gradient is controlled by the interaction between the South Pacific Anticyclone, the Andean rain shadow, and the Humboldt Current. Despite these extreme arid conditions, the coastal zone is characterized by the recurrent presence of fog associated with marine stratocumulus clouds, which, upon interacting with the coastal range, generate persistent fog banks over land. Marine fog constitutes the main water source for highly specialized ecosystems such as fog oases and fog-dependent forests distributed along this gradient. In addition to fog and rainfall, dew has also been recognized as an important water source for biological communities. While the meteorology of these water inputs is well documented, their combined influence on surface soil moisture and temperature dynamics remains poorly understood.This study evaluated the ecohydrological response of surface soil (2 cm depth) to atmospheric water regimes at four fog-dependent ecosystems (20°S-32°S): Alto Patache Research Station (hyperarid), Pan de Azúcar National Park (arid), Bosque Fray Jorge National Park (semiarid), and El Boldo Private Park (Mediterranean), during winter and spring 2025.During the winter-spring study period, results reveal a marked north-south increase in rainfall, from 0.2 mm at Alto Patache to 155 mm at El Boldo, whereas fog exhibited an inverse pattern, peaking at the hyperarid site (>1,100 L m⁻²) and reaching minimum values in the Mediterranean zone (41 L m⁻²). Dew emerged as a relevant water source in arid and hyperarid sites (≈31 L m⁻²), exceeding values in semiarid and Mediterranean environments (10 and 26 L m⁻², respectively). Soil moisture dynamics indicate that Mediterranean and semiarid sites exhibit high temporal variability driven by rainfall pulses (mean ≈0.14 m³ m⁻³, SD = 0.055, and 0.06 m³ m⁻³, SD = 0.018, respectively), whereas hyperarid and arid sites maintain relatively stable moisture regimes (SD ≈ 0.0075) closely associated with fog and dew at weekly timescales. At daily scales, soil temperature showed significant negative correlations with non-rainfall water inputs across all sites, highlighting fog and dew as dominant thermal regulators that buffer soil heating.We conclude that soil moisture and temperature regimes along this aridity gradient are governed by distinct hydrological drivers. A hydrological compensation mechanism emerges, whereby fog and dew sustain soil moisture and regulate soil temperature during rainless periods, particularly under hyperarid conditions. These findings underscore the critical role of non-rainfall water inputs in maintaining the ecohydrological resilience of drylands soils under future climate change.