Dew Formation Research Articles

Thermal regime of semi-natural dew collector’s perspective for afforestation of semi-arid landscapes

Waste rock dumps in the aftermath of pegmatite mining enable the growth of healthy populations of Larix sibirica in, for the forest unsuitable semi-arid steppe habitat, the Khentii Mountains, Mongolia. Trees can thrive in such extreme habitats due to water vapour condensation and adsorption in the topsoil of a dump. During the growing season 2015–2017, continual measurement of thermal regime (hourly) was carried out at the depths of 10, 30 and 60 cm in the dumps and surrounding steppes. At the depth of 10 cm, temperatures (up to 40% of cases) enabling dew formation in dumps, in the time period of the highest possible air humidity (2 a.m. to 8 a.m.) were confirmed there. The suitable temperature conditions to form dew were found primarily at the beginning of the growing season characterized by a low precipitation. Later in the growing season with the following increasing precipitation, the temperature potential of dumps for dew formation decreased continuously. The cross-correlation indicated active exchange of heat between the atmosphere and the dump up to the depth of 30 cm. The outcomes further indicate that water vapour adsorption shall contribute significantly to the moisture regime of dumps and the effective porosity of sandy soils of dumps is likely to form ideal conditions for it. The construction thickness of the cover soil material between the depths of 30 and 60 cm with the predefined physico-chemical properties can be recommended to augment the potential of the dew yield in future projects. Effective water vapour condensation and adsorption may support success of landscape afforestation or reclamation of mining areas in arid or semi-arid conditions. • Thermal regime of waste rock dumps allows water vapour condensation. • Waste rock dumps allow successful growth of trees away from natural forest habitat. • Waste rock dumps represent sustainable solution for reforestation of arid regions.

Salt Spray Distribution and Its Impact on Vegetation Zonation on Coastal Dunes: a Review

Salt spray mainly originates from the bursting of bubbles in breaking waves and is often considered as one of the dominant factors contributing to vegetation zonation in coastal dunes. In this paper, the literature on salt spray distribution and impact on dune plants are reviewed. Salt spray distribution is greatly affected by wave energy, wind conditions, distance from the coast, topography, vegetation, precipitation, and sand/soil properties. The amount of salt accumulation and trapping efficiency of the vegetative canopy are largely dependent on the plant characteristics such as architecture and leaf morphology. Salt concentrations in sand mainly vary with soil texture. Salt spray has negative impacts on plant growth and can cause water stress, promote tissue necrosis and leaf loss, reduce stomatal conductance, water use efficiency, photosynthesis, affect assimilates, or hormone supply to the growing organs. Damage to plants is increased by sand and wind abrasion and insect damage on leaves. High humidity, dew formation, light drizzle, and fog increase the rates of salt uptake by plant leaves. Plant seedlings and reproductive organs are more significantly affected by salt spray compared with mature plants and plant leaves respectively. Salt spray can also provide nutrition to plants particularly in coastal dunes with lower soil nutrition and salt accumulation rates. Species near the sea often show phenological, morphological, and physiological adaptations to salt spray including dormant times/seasons, low heights, compacted and asymmetrical canopies, unique leaf morphologies and/or orientations, dense hairs, rigid cuticles, and closed stomata. Surfactants produced from human activities can aggravate the damage on plants at average salt spray levels. Methods to trap salt vary considerably in the literature, and results from different studies may not be comparable due to trap type, placement, and landscape position. Greenhouse versus field experiments and sampling may not always be compatible. The relations between salt spray distribution and vegetation zonation will be further complicated under climate change and human activities.

Modeling Long-Term Temporal Variation of Dew Formation in Jordan and Its Link to Climate Change

In this study, we performed model simulations to investigate the spatial, seasonal, and annual dew yield during 40 years (1979–2018) at ten locations reflecting the variation of climate and environmental conditions in Jordan. In accordance with the climate zones in Jordan, the dew formation had distinguished characteristics features with respect to the yield, seasonal variation, and spatial variation. The highest water dew yield (an overall annual mean cumulative dew yield as high as 88 mm) was obtained for the Mountains Heights Plateau, which has a Mediterranean climate. The least dew yield (as low as 19 mm) was obtained in Badia, which has an arid climate. The dew yield had a decreasing trend in the past 40 years due to climate change impacts such as increased desertification and the potential of sand and dust storms in the region. In addition, increased anthropogenic air pollution slows down the conversion of vapor to liquid phase change, which also impacts the potential of dew formation. The dew yield showed three distinguished seasonal patterns reflecting the three climates in Jordan. The Mountains Heights Plateau (Mediterranean climate) has the highest potential for dew harvesting (especially during the summer) than Badia (semi-arid climate).

Foliar water uptake in arid ecosystems: seasonal variability and ecophysiological consequences.

Foliar water uptake (FWU) has been reported for different species across several ecosystems types. However, little attention has been given to arid ecosystems, where FWU during dew formation or small rain events could ameliorate water deficits. FWU and their effects on leaf water potential (ΨLeaf) were evaluated in grasses and shrubs exploring different soil water sources in a Patagonian steppe. Also, seasonal variability in FWU and the role of cell wall elasticity in determining the effects on ΨLeaf were assessed. Eleven small rain events (< 8mm) and 45days with dew formation were recorded during the study period. All species exhibited FWU after experimental wetting. There was a large variability in FWU across species, from 0.04mmolm-2 s-1 in species with deep roots to 0.75mmolm-2s-1 in species with shallow roots. Species-specific mean FWU rates were positively correlated with mean transpiration rates. The increase in ΨLeaf after leaf wetting varied between 0.65MPa and 1.67MPa across species and seasons. The effects of FWU on ΨLeaf were inversely correlated with cell wall elasticity. FWU integrated over both seasons varied between 28molm-2 in species with deep roots to 361molm-2 in species with shallow roots. Taking into account the percentage of coverage of each species, accumulated FWU represented 1.6% of the total annual transpiration of grasses and shrubs in this ecosystem. Despite this low FWU integrated over time compared to transpiration, wetting leaves surfaces can help to avoid larger water deficit during the dry season.

Water vapor variability in the Atacama Desert during the 20th century

This study focuses on integrated water vapor (IWV) which is the main source for precipitation, fog and dew formation in the Atacama Desert in northern Chile. In order to study its long-term variability, a consistent meteorological record is needed. Here, we utilize the European Centre for Medium-Range Weather Forecasts' reanalysis ERA-20C which provides IWV among other atmospheric variables over the course of the entire 20th century (1900–2010). In this two fold study, we first present a validation of ERA-20C IWV for the Atacama and the bordering southeast Pacific region. Comparisons to satellite observations, i.e. the Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite data record and the Moderate Resolution Imaging Spectroradiometer measurements, for overlapping time periods prove the suitability of ERA-20C to study IWV variability. Assessment of the observation feedback in ERA-20C reveals a higher uncertainty for the beginning of the 20th century when fewer observations are assimilated. Nevertheless, departures of the assimilated observations do not show a systematic bias in space or time supporting suitability of ERA-20C for long-term investigations. In the second part of the study, we describe the IWV variability over the course of the 20th century. Deviations from the long-term mean greater than 30% are found on an inter-annual time scale over the continental Atacama. Furthermore, we investigate potential drivers of the IWV variability such as the Pacific Decadal Oscillation (PDO) and the El Niño Southern Oscillation (ENSO) phenomenon. The relationship between the local IWV and these large scale indices depends on region and season. For instance, during austral summer, La Niña conditions yield overall greater IWV variability in the Atacama allowing both drier and even more pronounced wetter extremes than El Niño conditions.

Urban-rural moisture contrast: Regulator of the urban heat island and heatwaves’ synergy over a mediterranean city

The current study observed the effect of the synergistic interaction of urban heat island (UHI) and heatwaves (HWs) which is different from the sum of their separate effects on the medium-sized town of Nicosia, Cyprus. From an analysis of hourly meteorological records of eight consecutive years (2007–2014) we defined HWs with respect to air temperature (T95-over the 95th percentile air temperatures) as well as the heat index (HI65-heat index over 65degC) and studied their effects on the local UHI phenomenon. Both heatwave types were characterized by increased air temperature, lower wind speed and increased absolute humidity. HWs defined using the heat index (HI65) occurred more frequently and persisted for a longer period of time. UHI was intensified to about 0.9–1.3 °C during daytime hours under both HW definitions which was attributed to the evaporation of dew deposited on the upper top layer of soil that suppressed higher temperatures in the rural station due to a prolonged cooling effect. Model estimates of dew formation overnight and evaporation in the morning hours are hypothesized to be the main contributing factor in keeping rural air temperatures lower, thus increasing the UHI intensity. The results emphasize the critical role of latent cooling and evapotranspiration as a mitigation factor affecting extreme local temperatures.

Spatial and Temporal Investigation of Dew Potential based on Long-Term Model Simulations in Iran

Since water shortage has been a serious challenge in Iran, long-term investigations of alternative water resources are vital. In this study, we performed long-term (1979–2018) model simulation at seven locations (costal, desert, mountain, and urban conditions) in Iran to investigate temporal and spatial variation of dew formation. The model was developed to simulate the dew formation (water and ice) based on the heat and mass balance equation with ECMWF-ERA-Interim (European Centre for Medium-Range Weather Forecasts–Re-Analysis) meteorological data as input. According to the model simulation, the maximum mean yearly cumulative dew yield (~65 L/m2) was observed in the mountain region in the north part of Iran with a yearly mean cumulative dew yield was ~36 L/m2. The dew yield showed a clear seasonal variation at all selected locations with maximum yields in winter (mean monthly cumulative 3–8 L/m2 depending on the location). Here we showed that dew formation is frequent in northern Iran. In other areas, where there was suffering from water-stress (southern and central parts of Iran), dew can be a utilized as an alternative source of water. The dew yield during 2001–2014 was lower than the overall mean during the past 40 years a result of climate change in Iran.

Light on the cell cycle of the non-photosynthetic bacterium Ramlibacter tataouinensis

Ramlibacter tataouinensis TTB310, a non-photosynthetic betaproteobacterium isolated from a semi-arid region of southern Tunisia, forms both rods and cysts. Cysts are resistant to desiccation and divide when water and nutrients are available. Rods are motile and capable of dissemination. Due to the strong correlation between sunlight and desiccation, light is probably an important external signal for anticipating desiccating conditions. Six genes encoding potential light sensors were identified in strain TTB310. Two genes encode for bacteriophytochromes, while the four remaining genes encode for putative blue light receptors. We determined the spectral and photochemical properties of the two recombinant bacteriophytochromes RtBphP1 and RtBphP2. In both cases, they act as sensitive red light detectors. Cyst divisions and a complete cyst-rod-cyst cycle are the main processes in darkness, whereas rod divisions predominate in red or far-red light. Mutant phenotypes caused by the inactivation of genes encoding bacteriophytochromes or heme oxygenase clearly show that both bacteriophytochromes are involved in regulating the rod-rod division. This process could favor rapid rod divisions at sunrise, after dew formation but before the progressive onset of desiccation. Our study provides the first evidence of a light-based strategy evolved in a non-photosynthetic bacterium to exploit scarse water in a desert environment.

Coupled rainfall and water vapour stable isotope time series reveal tropical atmospheric processes on multiple timescales

AbstractHigh‐frequency stable isotope data are useful for validating atmospheric moisture circulation models and provide improved understanding of the mechanisms controlling isotopic compositions in tropical rainfall. Here, we present a near‐continuous 6‐month record of O‐ and H‐isotope compositions in both water vapour and daily rainfall from Northeast Australia measured by laser spectroscopy. The data set spans both wet and dry seasons to help address a significant data and knowledge gap in the southern hemisphere tropics. We interpret the isotopic records for water vapour and rainfall in the context of contemporaneous meteorological observations. Surface air moisture provided near‐continuous tracking of the links between isotopic variations and meteorological events on local to regional spatial scales. Power spectrum analysis of the isotopic variation showed a range of significant periodicities, from hourly to monthly scales, and cross‐wavelet analysis identified significant regions of common power for hourly averaged water vapour isotopic composition and relative humidity, wind direction, and solar radiation. Relative humidity had the greatest subdiurnal influence on isotopic composition. On longer timescales (weeks to months), isotope variability was strongly correlated with both wind direction and relative humidity. The high‐frequency records showed diurnal isotopic variations in O‐ and H‐isotope compositions due to local dew formation and, for deuterium excess, as a result of evapotranspiration. Several significant negative isotope anomalies on a daily scale were associated with the activity of regional mesoscale convective systems and the occurrence of two tropical cyclones. Calculated air parcel back trajectories identified the predominant moisture transport paths from the Southwest Pacific Ocean, whereas moisture transport from northerly directions occurred mainly during the wet season monsoonal airflow. Water vapour isotope compositions reflected the same meteorological events as recorded in rainfall isotopes but provided much more detailed and continuous information on atmospheric moisture cycling than the intermittent isotopic record provided by rainfall. Improved global coverage of stable isotope data for atmospheric water vapour is likely to improve simulations of future changes to climate drivers of the hydrological cycle.

Effects of Wilting and Dew on the Water Isotope Composition of Detached Grass in Temperate Grassland.

Understanding the water isotopes in feed products derived from grass is fundamental for tracing domestic animal products. Grass silage water was reported to have fewer heavy isotopes than fresh grass, but it is still unknown whether dew formation (either dewfall or dewrise), exchange with soil water, or other processes override the expected enrichment of heavy isotopes due to wilting. The isotopic variations of water (δ2H, δ18O) in fresh grass and cut grass during wilting on soil and on plastic were compared in this study. Drying enriched heavier isotopes, but this was overridden by three processes that finally caused low δ2H and δ18O values: (i) the adsorption of humidity from the surroundings, (ii) the exchange with humidity, and (iii) the depletion of heavy water isotopes close to organic surfaces, called the surface effect, which was the most dominant effect at the end of drying when the water content became low.

Wet-Dry Cycling Delays the Gelation of Hyperbranched Polyesters: Implications to the Origin of Life.

In extant biology, biopolymers perform multiple crucial functions. The biopolymers are synthesized by enzyme-controlled biosystems that would not have been available at the earliest stages of chemical evolution and consist of correctly sequenced and/or linked monomers. Some of the abiotic “messy” polymers approximate some functions of biopolymers. Condensation polymers are an attractive search target for abiotic functional polymers since principal polymers of life are produced by condensation and since condensation allows for the accurate construction of high polymers. Herein the formation of hyperbranched polyesters that have been previously used in the construction of enzyme-like catalytic complexes is explored. The experimental setup compares between the branched polyesters prepared under mild continuous heating and the wet-dry cycling associated with environmental conditions, such as dew formation or tidal activities. The results reveal that periodic wetting during which partial hydrolysis of the polyester occurs, helps to control the chain growth and delays the gel transition, a mechanism contributing to the tar formation. Moreover, the NMR and mass spec analyses indicate that continuously dried samples contain higher quantities of crosslinked and macrocyclic products, whereas cycled systems are enriched in branched structures. Ostensibly, environmental conditions have the ability to exert a rudimentary pressure to selectively enrich the polyesterification products in polymers of different structures and properties. At the early stages of chemical evolution, in the absence of biological machinery, this example of environmental control could have been for selectivity in chemical systems. As expected in marginally controlled systems, the identification of each component of the heterogeneous system has proved challenging, but it is not crucial for drawing the conclusions.

Stabilisation of crustal sand layer using biocementation technique for wind erosion control

Abstract This paper examines biocementation via the microbial-induced carbonate precipitation (MICP) process as an appropriate and promising new technology for stabilisation of loose sand and silty sand deposits as a method to mitigate wind erosion. The technique involves spray treating the sand surface layer with a mixture of cementation and bacterial-cell solutions, the ensuing reactions causing calcite precipitation to occur between the sand grains, thereby lightly cementing them together over time. The bench-scale experimental programme presented investigates the proposed technique’s effectiveness for stabilisation of silica and carbonate sands with different gradations, determination of the optimal reagent concentrations, the time-dependent shear strength development for the crustal sand layer following single- and double-MICP spray treatments, as well as wind tunnel experiments. Of particular novelty were investigations of the effect of dew formation on crustal shear strength development with curing period and the efficiency of the MICP treatment for the outdoor environment compared to laboratory-controlled test conditions. The wind tunnel experiments demonstrated that 28-day cured singly MICP-spray-treated crustal sand layers were stable to simulated 20 m·s −1 winds measured at 20 cm above the layer surface.

The enigmatic absence of cyanobacterial biocrusts from the Namib fog belt: Do dew and fog hold the key?

Although considered as pioneering organisms of biocrusts, cyanobacterial biocrusts are scarce and even absent from the Namib fog belt, which is inhabited, however, by luxurious lichen-dominated crusts. While previously proposed that the phenomenon may stem from a low rainfall frequency, it is suggested herein that it may stem from a negative balance of carbon. This explanation is based on published data on photosynthesis of biocrusts along with an analysis of dew and fog formation. Lush cover of lichens at habitats with no cyanobacteria also casts doubt on the widely accepted view that regards cyanobacteria as a required component in biocrust succession.

Dew Yield and Its Influencing Factors at the Western Edge of Gurbantunggut Desert, China

Dew is a significant water resource in arid desert areas. However, information regarding dew is scarce because it is difficult to measure due to the harsh environment of locations such as Gurbantunggut Desert, China. In this study, a non-destructive field experiment was conducted from 2015 to 2018 at a desert test station located in the western edge of the Gurbantunggut Desert, using a calibrated leaf wetness sensor (LWS) to measure dew yield. The results are as follows: (1) Dew formed after sunset with the atmospheric temperature gradually dropping and evaporated after sunrise with the temperature increasing in the second morning. (2) Dew was featured as ‘high frequency and low yield’. The average daily dew yield during dew days was 0.10 mm with a daily maximum of 0.62 mm, while dew days accounted for 44% of the total monitoring days, with a monthly maximum of 25 days. Compared with rainfall, dew days were two times as frequent as rainy days, while the average annual dewfall (12.21 mm) was about 1/11th of the average annual rainfall (134.6 mm), which indicates the dew contribution to regional water balance is about 9%. (3) March–April and October–November are the main periods of dew occurrence in this region because accumulated snow begins to melt slowly in March–April, providing sufficient vapor for dew formation, and the air temperature difference between day and night in October–November is the highest in the year, meaning that the temperature drops rapidly at night, making it easier to reach the dewpoint for vapor condensation. (4) Daily dew yield (D) was positively correlated to relative humidity (RH) and the difference between soil temperature at 10 cm below the ground and surface soil temperature (Tss), and negatively correlated to wind speed (V), air temperature (Ta), surface soil temperature (Ts), cloud cover (N), dewpoint temperature (Td) and the difference between air temperature and dewpoint temperature (Tad). It should be noted that the measured values of all factors above were the average value of the overnight period. The multivariate regression equation, D = −0.705 + 0.011 × RH − 0.006 × N − 0.01 × V, can estimate the daily dew yield with the thresholds of the parameters, i.e., RH &gt; 70%, N &lt; 7 (oktas) and V &lt; 6 m/s.

Quantification and Prediction of Nighttime Evapotranspiration for Two Distinct Grassland Ecosystems

AbstractEvapotranspiration (ET) is, after precipitation, the second largest flux at the land surface in the water cycle and occurs mainly during daytime. Less attention has been given to water fluxes from the land surface into the atmosphere during nighttime (i.e., between sunset and sunrise). The nighttime ET (ETN) may be estimated based on models that use meteorological data; however, due to missing experimental long‐term data, the verification of ETN estimates is limited. In this paper, the amount of ETN for two grassland ecosystems was determined from highly temporally resolved and precise weighing lysimeter data. We found that annual ETN ranged between 3.5% and 9.5% of daytime annual ET (ETD) and occurred mainly during wet soil and canopy surface conditions, which suggests that ETN is largely related to evaporation. ETN was positively correlated with wind speed. Dew formation, ranging from 4.8% to 6.4% of annual precipitation, was in absolute terms larger than ETN. The prediction of ETN with the Penman‐Monteith model improved if the aerodynamic and surface resistance parameters were based on vegetation height observations and the nighttime stomatal resistance parameter was assumed to be zero. The occurrence of hot days during the observation period showed to increase average ETN rates. Our results suggest that ETN can be observed with precision weighing lysimeters, was a not negligible component in the water balance of the grassland ecosystems, and thus needs more attention when simulating land surface hydrological processes.

On the Formation and Development of Radiation Fog: An Observational Study

Observations from the Local and Non-local Fog EXperiment field campaign are used to investigate the formation and initial development of radiation fog. Data from six locations have been selected: five sites in Shropshire, and one in Bedfordshire, UK. These data show that during night-time clear-sky conditions, thermally-stable radiation fog only forms when the vertical velocity variance near the ground (at 2 m) decreases to 0.002–0.005 m2 s−2 or less. The variation in this threshold appears to be a function of the vertical relative humidity gradient near the ground. When the vertical velocity variance exceeds these values, saturation may still occur near the ground, but fog formation is inhibited due to the more efficient transport of moisture to the ground in the form of dew. Furthermore, once stable radiation fog forms, any increase in the vertical velocity variance to values greater than 0.002–0.005 m2 s−2 may cause the fog to dissipate. The subsequent development of shallow stable fog into deeper, weakly-unstable fog is also examined. Possible mechanisms for this are discussed, including in situ processes and non-local larger scale processes. Clear evidence of the latter is presented, but the relative importance of in situ and non-local processes for fog deepening requires further clarification.

Dew frequency across the US from a network of in situ radiometers

Abstract. Dew formation is a ubiquitous process, but its importance to energy budgets or ecosystem health is difficult to constrain. This uncertainty arises largely because of a lack of continuous quantitative measurements on dew across ecosystems with varying climate states and surface characteristics. This study analyzes dew frequency from the National Ecological Observatory Network (NEON), which includes 11 grasslands and 19 forest sites from 2015 to 2017. Dew formation is determined at 30 min intervals using in situ radiometric surface temperatures from multiple heights within the canopy along with meteorological measurements. Dew frequency in the grasslands ranges from 15 % to 95 % of the nights with a strong linear dependency on the nighttime relative humidity (RH), while dew frequency in the forests is less frequent and more homogeneous (25±14 %, 1 standard deviation – SD). Dew mostly forms at the top of the canopy for the grasslands due to more effective radiative cooling and within the canopy for the forests because of higher within the canopy RH. The high temporal resolution of our data showed that dew duration reaches maximum values (∼6–15 h) for RH∼96 % and for a wind speed of ∼0.5ms-1, independent of the ecosystem type. While dew duration can be inferred from the observations, dew yield needs to be estimated based on the Monin–Obukhov similarity theory. We find yields of 0.14±0.12mmnight-1 (1 SD from nine grasslands) similar to previous studies, and dew yield and duration are related by a quadratic relationship. The latent heat flux released by dew formation is estimated to be non-negligible (∼10Wm-2), associated with a Bowen ratio of ∼3. The radiometers used here provide canopy-averaged surface temperatures, which may underestimate dew frequency because of localized cold points in the canopy that fall below the dew point. A statistical model is used to test this effect and shows that dew frequency can increase by an additional ∼5 % for both ecosystems by considering a reasonable distribution around the mean canopy temperature. The mean dew duration is almost unaffected by this sensitivity analysis. In situ radiometric surface temperatures provide a continuous, non-invasive and robust tool for studying dew frequency and duration on a fine temporal scale.

Characteristics of Dew Formation in the Semi-Arid Loess Plateau of Central Shaanxi Province, China

Compared to rain, dew is an important supplementary source of water for the survival of certain plants and animals in drylands. However, the hydrology of dew has not yet been fully investigated due to difficulties in measuring the amount and duration of it. In this study, a 3-year in-situ monitoring experiment was conducted from 2014 to 2016 in the semi-arid Sanyuan County, Shaanxi Province of China, using a leaf wetness sensor (LWS) and four associated meteorological instruments. Results showed that the average annual total dewfall was 32.8 mm with a daily maximum of 0.88 mm. The majority of daily dew occurred in the night from 18:00 to 8:00 with the maximum condensation rate occurring at around 4:00. The maximum dew residence time was about 18 h/day on the dew days in all seasons. However, the actual dew production period was about 14 h in spring (March–May), autumn (September–November), and winter (December–February), and only 11 h in summer (June–August). The maximum intensity and amount of dew always occurred in autumn (with an average amount of 12.2 mm or 37% of the annual total), followed closely by spring (11.4 mm, 35%), with much less in summer (6.6 mm, 20%) and winter (2.6 mm, 8%). The annual dew distribution by months showed a double crest variation, with two peaks in April–May and October–November, and two valleys in January–February and July. Comparatively, annual dewfall is only about 1/18th of the rainfall in this region, but the number of dew days (224 days, or 61% of year) is 2.6 times that of rain days (87 days, 24%), making dew a critical supplementary source of water for mitigating dry periods and supporting native plants and animals. Rain and dew are highly complementary as dew occurs in cloudless nights while the rain occurs in different and on much fewer occasions in the region. The dew amount was highly and positively correlated to the relative humidity of the air above the threshold of 81% (r = 0.78, p &lt; 0.01), negatively correlated to the difference between air temperature Ta and dewpoint Td, when (Ta − Td) is less than 4 °C (r = −0.66, p &lt; 0.01), and weakly correlated to wind speed (0.2 to 2 m·s−1), wind direction, surface soil moisture, and temperature. In the Sanyuan region, two general wind directions, 30°–90°and 210°–270°, were more favorable for the formation of dew.

Dew Can Prolong Photosynthesis and Water Status During Drought in Some Epiphytic Bromeliads From a Seasonally Dry Tropical Forest

Dew can represent an alternate water source in epiphytic bromeliads. However, the physiological relevance of dew to withstand the dry season, within seasonal forests, is not fully understood. To study the effect of dew deposition in the physiological response of four Tillandsia species with contrasting morphologies, we performed an experiment in the tropical dry deciduous forest of Dzibilchaltún, Mexico, during the transition from the wet to the dry season. Half of the individuals were covered every night with a plastic tarp to prevent dew deposition. Environmental variables were monitored, and physiological variables (relative water content, leaf succulence, nocturnal tissue acidification and electron transport rate) were measured at the beginning and end of the experiment. We found that throughout the drought, there was consistent nighttime dew formation for &gt;4 h. Both the time the leaves spent at a temperature below dew point of the air and the effect on water and carbon metabolism was species -specific, as evidenced by the comparison among the exposed and covered (dew -deprived) plants. Tillandsia elongata and Tillandsia brachycaulos had longer times of dew formation and showed higher water content at the end of the experiment when exposed to dew, the latter species also had a significant effect of dew on nocturnal acidity. In contrast, neither Tillandsia yucatana nor Tillandsia fasciculata seemed to be using dew as a relevant source of water during the dry period. We discuss the species’ morphoanatomical traits that may be related to the differences in dew formation and use.

Sustainable Water Harvesting Technique by Condensation of Water through Atmosphere in An Optimized Approach for Future Cities in India

Water is one of the vital needs of humans. Many rural areas lack the water infrastructure to fulfil their basic needs. About 8-10% of the people lack safe drinking water which causes health issues and deaths. Water harvesting structures (WHS) is a vertical conical structure designed to harvest potable water from the atmosphere. In this research work, WHS is constructed by using material such as bamboo, polyester mesh which absorbs the water molecules from humid mist present in atmosphere. This absorbed water passes through the mesh and forms water droplets through condensation and is collected under the action of gravity. Considering the effect of large formation of fog, seasonal rain and dew during majority of the seasons in a year, WHS was constructed keeping Rasayani (Maharashtra) as the study area. Due to the geographical assistance provided by this study area, it was possible to extract water from air at high altitude hence proved to be a sustainable method for the collection of water from atmosphere. Water harvested in this WHS was pure and can be utilized for various domestic purpose like drinking, cooking, etc. This research signifies that by constructing WHS by locally available material, a sustainable low initial cost structure was constructed with less maintenance and zero energy requirement.