Water vapor adsorption (WVA), a non-rainfall water input, is a poorly documented phenomenon despite its role in regulating water and energy fluxes in soils of coastal deserts. Water vapor movement towards the soil surface and its absorption by the soil occurs whenever the atmospheric water potential is higher than that of the air-filled soil pores. The latter is influenced by soil characteristics, in particular the soil surface area and pore connectivity. Thus, it is expected that under similar atmospheric conditions, absorption of water vapor will be determined by soil characteristics. We carried out a detailed field trial in which we compared two loamy soils with different salt content.Water vapor absorption was measured using micro-lysimeters (MLs) instrumented with relative humidity (RH) and temperature sensors at depths 0.5cm, 2cm, 5cm, 10cm, and 45cm in both MLs during the 2022 and 2023 summers. Total absorption was determined as the increase in mass from a minimum (obtained during late afternoon) to a peak observed on the next day before sunrise. Concurrent changes in soil water potential at each depth were computed by applying the Kelvin equation.Relative humidity in both soils was low during the entire season with the average computed water potential values being lower in the high salt content soil. The total daily water vapor absorption was lower in the low salt content soil, and the rate of absorption was different . The temperature and RH distribution patterns with depth also differed consistently throughout the measuring season for both soils. The effect of salt on water vapor absorption will be highlighted.

Primary productivity in arid zones is limited by the lack of water and soil nutrients. Conveying and storing flood water in plots surrounded by embankments allows agricultural activity in areas where there is generally insufficient rainfall to sustain agricultural production. The efficient exploitation of the stored water was achieved by intercropping trees with an annual crop and pruning the former before planting the intercrop. This approach minimized competition for water and solar radiation. However, in order to ensure the long-term viability of such a system nutrients have to be added to the soil in order to compensate for the uptake of the intercrop, Nitrogen being the main element. The composted leaves of a leguminous shrub-like tree incorporated into the soil could satisfy the nitrogen demand of the intercrop. We tested this approach in a simulated runoff agroforestry system with fast-growing acacia (A. saligna) trees as the woody component and maize (Zea mays L.) as intercrop for two consecutive seasons. Ten treatments were applied (radical pruning before intercrop planting, compost application and planting of the intercrop as factors) and the below- and above-ground effects and interactions examined. Pruning the trees canopies changed the trees’ root spatial and temporal distribution, allowing the annual crop to develop between the trees. Addition of compost significantly increased intercrop yield irrespective of the presence of the woody component while the presence of the intercrop did not affect the productivity of the trees. The highest productivity was obtained for the pruned trees, intercrop and added compost treatment. A significant increase in the presence of tree roots was observed for the deeper parts of the soil profile for the pruned trees, intercrop and added compost treatment. The addition of composted leaves from the leguminous woody component to the intercrop resulted in a very high water use efficiency of the water stored in the soil.

In our experimental research, we examined the relative influence of radiation and transpiration on the canopy temperature of urban trees in a hot-arid climate, from the viewpoint of microclimatic modification and pedestrian thermal stress. Our main objective was to identify, through controlled observations in an outdoor urban setting, the role of (a) cumulative shading by multiple layers of leaves and (b) the cooling induced by stomatal conductance and transpiration. Systematic measurements were conducted to simultaneously compare these regulating effects under conditions of water stress, in which leaf transpiration was negligible, and under control conditions of full transpiration ensured by regular irrigation. We found that the radiative temperature of leaves on the underside of urban tree canopies is mainly regulated by the cumulative shading effect of the multiple leaf layers above and to a lesser extent by their rate of transpiration. These findings have important implications for the design and maintenance of urban green spaces, especially as ongoing local and regional climate trends cause many cities to become both hotter and drier. By considering the ways in which we can use shade trees to moderate pedestrian thermal stress, and at the same time conserve precious water resources, we can envision a path toward greater urban resilience and an enhanced quality of urban life.

Burrows are animal-built structures that can buffer their occupants against the vagaries of the weather and provide protection from predators. We investigated whether the trapdoors of wolf spider (Lycosa sp.; temporary working name "L. hyraculus") burrows in the Negev Desert serve to maintain favorable environmental conditions within the burrow by removing trapdoors and monitoring the ensuing temperature and relative humidity regime within them. We also monitored the behavioral responses of “L. hyraculus” to trapdoor removal at different times of the day and in different seasons. “L. hyraculus” often spun silk mesh in their burrow entrances in response to trapdoor removal during the day, possibly to deter diurnal predators. The frequency of web-spinning peaked on summer mornings, but spiders began spinning webs sooner after trapdoor removal later in the day. In addition, we monitored temperature and relative humidity in artificial burrows in the summer during the morning and at midday. At noon, air temperature (Ta) at the bottom of open burrows increased by <1 °C more than in covered burrows, but water vapor pressure in burrows did not change. The relatively small increase in Ta in uncovered burrows at midday can probably be ascribed to the penetration of direct solar radiation. Thus, air temperature and humidity at the bottom of the burrow are apparently decoupled from airflow at the surface.

In arid and semiarid environments non-rainfall water inputs (NRWI) are an important source of water. In Israel's Negev desert direct absorption of atmospheric water vapor is the dominant NRWI and is strongly affected by soil properties, in particular clay content. The presence of a surface crust layer, whose physical and physico-chemical properties are substantially different from those of the underlying undisturbed substrate will likely affect the absorption patterns. The objective of our study was to quantify the effect of soil type (loess vs. sand) and crust cover (crust vs. crust removed) on direct atmospheric water absorption. The loess soil samples were obtained in an open field adjacent to the Jacob Bluestein Institutes for Desert Research (BIDR), Ben-Gurion University of the Negev (30˚51’ N, 034˚46’ E, 470 m a.s.l); and the sand samples from the Nizzana Sand Dune area (30˚58’N, 034˚24’E, 226 m a.s.l.). The loess crusts were physically induced while those present on the sand samples were of biological origin. A field experiment was carried out in the open field adjacent to the BIDR. Four undisturbed 0.5 m depth soil samples (sand and loess with crust and with crust removed) were placed in micro-lysimeters and automatically weighed at 30 min. intervals. This field experiment was carried during the dry season of May to October 2016. The field study was supplemented with a laboratory experiment in which undisturbed samples (1,3, 7 and 10 cm) obtained from the above mentioned sites were used. Oven-dry samples were exposed during 6 days to constant temperature and relative humidity conditions (25±1 oC and 85±5 %, respectively) in sealed chambers. Mass changes were recorded at varying time intervals. The adsorption process in the field started in the late afternoon with the arrival of the sea breeze and ended with sun rise. On a daily basis the crusted loess sample adsorbed more water than the crusted sand sample, and the crust removed loess soil absorbed more water than the crust removed sand. The crusted samples generally absorbed less water than the corresponding non-crusted ones. The results of the laboratory tests showed that loess samples with crust and with crust removed absorbed similar water amounts for all sample depths throughout the study period. The crusted sand samples however absorbed systematically more water than the crust removed samples for all sample depths. We conclude that the higher resistance of crusts to gaseous flux, a result of their higher bulk density and smaller pores, does not limit water vapor flux into the deeper soil layers and does not explain the field results.

Micro-catchment systems (MCs) are designed to harvest and utilize rainwater, with the aim of supporting crop growth in arid regions. While MCs were traditionally built with shallow infiltration basins, recent research indicates that MCs with deeper basins lose less water to the atmosphere than MCs with shallower basins. Consequently, we can expect more water to infiltrate the soil and be available to trees grown in deeper MCs than those grown in shallow MCs. The reduction in the direct water loss is owed, to a large extent, to the decreased flux of incoming shortwave radiation reaching the surface in deeper basins. The degree to which the incoming shortwave radiation reaching the floor of the MC is reduced, in turn, depends on the system's dimensions and orientation, geographical location, canopy geometry, soil properties, date, and time. We present a model that calculates the incoming all-wave (short- and longwave) radiation flux densities reaching any point on the floor of a trench MC in which trees are planted. To add to previously developed models that considered direct radiation, diffuse radiation, and direct and diffuse radiation reflected downwards from the walls of the trench, the model accounts for possible shading and attenuation of the radiation caused by the presence of a canopy in the system. We have also added the component of longwave radiation, considering longwave radiation emitted from the atmosphere, from the canopy of trees planted within the system, and from the trench walls. We validated the model by comparing modeled results to field measurements inside a planted trench system. We used pyranometers to measure the incoming shortwave radiation and a 4-way net radiometer for the incoming longwave. Our results indicate that the model accurately depicts the diurnal course of shortwave and longwave radiation at different points on the floor of a N-S oriented trench MC and for different solar elevation angles. Simulations for the Negev Desert revealed that the presence of a canopy can strongly influence which trench configurations lead to the greatest decreases in incoming shortwave radiation. When a large canopy is present and the trench is wide, less radiation reaches the ground in N-S oriented trenches than in E-W oriented trenches. While the incoming longwave radiation at the bottom of the trench MC is higher than that on an equivalent horizontal surface at ground level, this increase is not enough to offset the decrease in shortwave radiation. The simulations indicate that the total incoming all-wave radiation (combined shortwave and longwave) inside trenches is less than that outside.

The main objective of the study was to assess the relative importance of the electrolyte concentration of rain drops and their kinetic energy on the infiltration rate of naturally crusted loess soil. A highly accurate portable rainfall simulator was used in this study. The effect of electrolyte concentration on infiltration rates was studied by comparing the runoff patterns observed using distilled or tap water. Similar infiltration curves were obtained for both treatments indicating that the effect of the electrolyte concentration of the applied water on infiltration was negligible. The effect of raindrop energy on infiltration rate was assessed by comparing the runoff characteristics of three treatments: fog, plot covered with dense mesh and no-surface protection. No runoff was observed in the fog treatment and the infiltration rates in the protected treatment were significantly higher than those of the unprotected treatment. The results of this study suggest that the momentum of drops hitting a naturally crusted loess soil significantly affect the infiltration process while the electrolyte concentration of the rain water does not meaningfully contribute to further crust development. Runoff coefficients derived from studies carried out with rainfall simulators that do not mimic the natural distribution of drop size and energy should be viewed with care.

Roof pond systems for passive cooling of buildings are often limited in their efficiency because of solar heating loads or insufficient ventilation. Here we test the performance of a roof cooling configuration that resembles a naturally-ventilated psychrometer – designed to maintain a temperature close to that of the ambient wet-bulb by employing an elevated shading structure which allows for a free flow of air and maximizes evaporation. Comparing the performance of this ‘psychrometric’ roof pond (PRP) with a control roof under hot-dry conditions, it was found that the internal surface temperature of the PRP was up to 15 °C lower and that cooling was equally effective whether the roof pond was fully or partially exposed to the night sky. Throughout the hours of a summer day, air temperature in the cell was maintained within accepted comfort limits while the reference cell was continuously overheated. An analysis of energy fluxes above the roof showed that both the modified radiation balance and the conversion of sensible to latent heat through evaporation were significant contributors to the dramatically reduced heat gain and cooling effectiveness. Due to its low water requirement and simplicity, the tested configuration could have a significant potential for resource-efficient cooling.

. At issue Drylands occupy about 41% of Earth’s land surface, and while eing home to about one third of the human population, they retain nly 8% of the world’s renewable water resources (Millennium cosystem Assessment, 2005). For thousands of years man has ried to skillfully manage this vital but scarce resource by collecting unoff water and utilizing it for irrigation (e.g., Evenari et al., 1971; roppelmann and Berliner, 2003). Water harvesting methods forerly developed for mere existence (Boers and Benasher, 1982) are owadays receiving renewed attention. Micro-catchment water harvesting systems, used in many dryand areas around the world (e.g., Critchley and Siegert, 1991) re systems by which runoff is collected from a contributng area, stored in an adjacent infiltration basin, and support ree growth during the dry season (Boers and Benasher, 1982). icro-catchment systems were developed and implemented in editerranean climates in which the dry season can be very long. In ∗ Corresponding author. E-mail address: agam@bgu.ac.il (N. Agam). ttp://dx.doi.org/10.1016/j.agrformet.2016.02.014 168-1923/© 2016 Elsevier B.V. All rights reserved. order to ensure tree production, non-productive water losses have to be minimized. Water losses mainly occur from the impounding area during the period during which free water is available and from the wet soil surface thereafter. The surface of the wetted area thus plays a major role (Zhang et al., 2013). Traditionally, the infiltration basins of micro-catchment systems were shallow (Fig. 1a) and deepening them significantly reduced evaporation from the soil surface (Zhang et al., 2013). It is, however, not practical to dig deep pits for each tree and the use of trenches has been proposed (Fig. 1b). The depth of the trench directly affects costs and it is therefore of interest to estimate the relation between trench geometry and water loss. The main driver for evaporation is the flux of short wave radiation that reaches the wetted surface. The first step in developing a comprehensive model to this effect, and the objective of the work reported herein is to model the short wave radiative fluxes for different trench geometries (depth/width and orientation). Solar radiation intensity at a given point is the sum of the direct beam radiation, solar radiation scattered during its passage through the atmosphere (diffuse radiation), and the radiation reflected downwards by the walls of the trench. The relative contribution, and thus the relative importance of each of the above mentioned N. Agam et al. / Agricultural and Forest Meteorology 221 (2016) 152–163 153

Micro-catchment water harvesting systems are systems by which runoff is collected from a contributing area, stored in an adjacent infiltration basin, and support tree growth during the dry season. Increase of the efficiency of such systems can be achieved by minimizing non-productive water losses, which mainly occur from the impounding area during the period during which free water is available and from the wet soil surface thereafter. Designing the infiltration basin as a trench can potentially meet this goal. The main driver for water loss through evaporation is the flux of short wave radiation that reaches the wetted surface. The first step in developing a comprehensive model to this effect, and the objective of the work reported herein is to model the short wave radiative fluxes for different trench geometries. The model computes the radiation reaching the floor of a trench at each point across the trench width accounting for the direct, diffuse, and reflected components. Model validation indicated that the model accurately depicts the diurnal course of radiation reaching the trench floor in both north-south and east west orientated trenches in both summer and winter. Simulations for the Negev Desert revealed distinct differences in the diurnal course of mean solar radiation reaching the trench floor between north-south and east-west orientations. During the rainy season (November through March) radiation load was found to be greater in the north-south orientation. Thus, aiming to reduce evaporative losses from trench-like runoff harvesting systems in the Negev, east-west orientated trenches are advantageous. (C) 2016 Elsevier B.V. All rights reserved.

Remote sensing has proved to be a consistent tool for monitoring water fluxes at regional scales. The triangle method, in particular, estimates the evaporative fraction (EF), defined as the ratio of latent heat flux (LE) to available energy, based on the relationship between satellite observations of land surface temperature and a vegetation index. Among other methodologies, this approach has been commonly used as an approximation to estimate LE, mainly over large semi-arid areas with uniform landscape features. In this study, an interpretation of the triangular space has been applied over a heterogeneous area in central Spain, using Landsat5-TM, Envisat-AATSR/MERIS and MSG-SEVIRI images. Some aspects affecting the model performance such as spatial resolution, terrain conditions, vegetation index applied and method for deriving the triangle edges have been assessed. The derived EF estimations have been validated against ground measurements obtained with scintillometer on a winter crop field during 2010–2011. When working with large spatial windows, removing areas with different topographic characteristics (altitude and slope) improved the performance of the methods. In addition, replacing the typically used NDVI with Leaf Area Index enhances the performance of the triangle method allowing a better characterization of the wet edge. Finally, results showed a relatively good performance for the EF estimates, with an RMSE of 0.11, 0.15 and 0.23 and R2 of 0.77, 0.41, and 0.24 for Landsat, Envisat and MSG satellites respectively, showing a scale dependency on the accuracy.

Rodent burrows are often assumed to be environments wherein the air has a high concentration of CO2. Although high burrow [CO2] has been recorded, many studies report burrow [CO2] that differs only slightly from atmospheric concentrations. Here, we advocate that one of the reasons for these differences is the penetration into burrows of air gusts (eddies), which originate in the turbulent boundary layer and prevent build-up of CO2. We have characterized the means by which burrows of Sundevall's jird, which are representative of the burrows of many rodent species with more than one entrance, are ventilated. Our results demonstrate that, even at low wind speeds, the random penetration of eddies into a burrow through its openings is sufficient to keep the burrow [CO2] low enough to be physiologically inconsequential, even in its deep and remote parts.