Environmental research is conducted to better understand drylands in a changing world
Current projects
Atmospheric-water capture by the world’s desert soils
Atmospheric water, or non-rainfall water inputs (NRWIs) are an important source of water in arid areas. The large area of arid regions and the frequent occurrence of NRWIs in these regions make them a critical, albeit largely overlooked, component of the global hydrological cycle. There is also increasing evidence that NRWIs can activate soil respiration, which implies that they could initiate CO2 flux.
Quantification of NRWIs, in the form of fog, dew, or water vapor adsorption, and how they affect the water, energy, and CO2 budgets, has mostly been done at local scales. The little that is known about the global extent of NRWIs, is known primarily about dew, the smallest of NRWI components to contribute moisture to soils in arid regions. Water vapor adsorption, on the other hand, is likely the most significant, yet the least studied, NRWI. We aim, for the first time, to make a global assessment of water vapor adsorption by the world’s desert soils, and of the potential implications for soil-atmosphere CO2 exchange.
Atmospheric water, or non-rainfall water inputs (NRWIs) are an important source of water in arid areas. The large area of arid regions and the frequent occurrence of NRWIs in these regions make them a critical, albeit largely overlooked, component of the global hydrological cycle. There is also increasing evidence that NRWIs can activate soil respiration, which implies that they could initiate CO2 flux.
Quantification of NRWIs, in the form of fog, dew, or water vapor adsorption, and how they affect the water, energy, and CO2 budgets, has mostly been done at local scales. The little that is known about the global extent of NRWIs, is known primarily about dew, the smallest of NRWI components to contribute moisture to soils in arid regions. Water vapor adsorption, on the other hand, is likely the most significant, yet the least studied, NRWI. We aim, for the first time, to make a global assessment of water vapor adsorption by the world’s desert soils, and of the potential implications for soil-atmosphere CO2 exchange.
CO2 flux initiated by non-rainfall water inputs
Where there is water, there is life!
And while NRWIs are relatively small fluxes, there is evidence of plants, lichens and microbes relying partly or mostly on NRWIs. Since much of the surface in arid and extremely arid regions is bare, activity in the soil itself is likely the largest component both in NRWI uptake and in subsequent CO2 exchange. We hypothesize that, in deserts, early morning peaks in CO2 emissions are activated by NRWIs.
CO2 concentrations are measured with soil CO2 chambers as well as with an eddy-covariance system, concurrently with actual NRWI measurements. Very initial results indicate an increase in CO2 concentration in the air immediately after sunrise, when the moisture content is highest and solar radiation starts adding energy to the system, may be a result of CO2 emission from the soil, initiated by NRWIs. Stay tuned!
Where there is water, there is life!
And while NRWIs are relatively small fluxes, there is evidence of plants, lichens and microbes relying partly or mostly on NRWIs. Since much of the surface in arid and extremely arid regions is bare, activity in the soil itself is likely the largest component both in NRWI uptake and in subsequent CO2 exchange. We hypothesize that, in deserts, early morning peaks in CO2 emissions are activated by NRWIs.
CO2 concentrations are measured with soil CO2 chambers as well as with an eddy-covariance system, concurrently with actual NRWI measurements. Very initial results indicate an increase in CO2 concentration in the air immediately after sunrise, when the moisture content is highest and solar radiation starts adding energy to the system, may be a result of CO2 emission from the soil, initiated by NRWIs. Stay tuned!
Effect of soil type and the presence of crust on non-rainfall water inputs
Non-rainfall water inputs (NRWIs), i.e., fog deposition, dew formation, and direct water vapor adsorption by the soil, may play a vital role in arid and semi-arid areas. The time interval during which water is adsorbed, and the total amount of adsorbed water, are controlled by various environmental factors. The ever changing atmospheric conditions are the main driver for the process, but the type of substrate (soil type and the existence/absence of a physical/biological crust layer) may play a major role. In this study we aim to quantify the effects of soil type (loess vs. sand) and surface type (bare vs. (bio)crusted sands) on the gain and posterior evaporation of NRWIs in the Negev highlands as a function of environmental conditions.
Non-rainfall water inputs (NRWIs), i.e., fog deposition, dew formation, and direct water vapor adsorption by the soil, may play a vital role in arid and semi-arid areas. The time interval during which water is adsorbed, and the total amount of adsorbed water, are controlled by various environmental factors. The ever changing atmospheric conditions are the main driver for the process, but the type of substrate (soil type and the existence/absence of a physical/biological crust layer) may play a major role. In this study we aim to quantify the effects of soil type (loess vs. sand) and surface type (bare vs. (bio)crusted sands) on the gain and posterior evaporation of NRWIs in the Negev highlands as a function of environmental conditions.
Does the Rose of Jericho harvest fog and dew water to live through dry spells?
We hypothesize that A. hierochintica (the True Rose of Jericho) has mechanisms to harvest atmospheric water based on its hairy leaf structure and its ability to tilt leaves relative to the stem. We predict that using these morphological structures, the plant can harvest water from the lower atmosphere and direct them toward its roots.
More to follow. Stay tuned.
--In collaboration with Merav Seifan, Ben-Gurion University of the Negev.
More to follow. Stay tuned.
--In collaboration with Merav Seifan, Ben-Gurion University of the Negev.
Cosmic-Ray Neutron Sensing technique for quantifying non-rainfall water inputs
Non-rainfall water inputs (NRWIs, i.e., fog, dew, and direct water vapor adsorption) are known to significantly contribute to the water cycle of drylands. Measurements of these inputs were thus attempted using various methods, most of which are point measurements that cannot account for the natural heterogeneity of desert soils. Cosmic-Ray Neutron Sensing (CRNS) is a novel technology to measure hydrogen in the environment averaging over larger areas in the range of 100 m-radius.
The small fluxes involved in NRWIs formation and evaporation challenge every methodology and push it to the limits of applicability. The overall aim of this proposed research is to test the ability of the CRNS sensor to accurately detect NRWIs. The technological characteristics and the physical context of CRNS make it currently to the most promising candidate to overcome the scale gap in NRWIs monitoring in the desert. If proved successful, this will be a novel and relevant tool for monitoring the water balance of arid and semi-arid areas, which is critical for the understanding of ecosystem dynamics, especially where water is a limiting resource.
--In collaboration with Martin Schrön and Steffen Zacharias, Helmholtz Centre for Environmental Research GmbH - UFZ, Germany
Non-rainfall water inputs (NRWIs, i.e., fog, dew, and direct water vapor adsorption) are known to significantly contribute to the water cycle of drylands. Measurements of these inputs were thus attempted using various methods, most of which are point measurements that cannot account for the natural heterogeneity of desert soils. Cosmic-Ray Neutron Sensing (CRNS) is a novel technology to measure hydrogen in the environment averaging over larger areas in the range of 100 m-radius.
The small fluxes involved in NRWIs formation and evaporation challenge every methodology and push it to the limits of applicability. The overall aim of this proposed research is to test the ability of the CRNS sensor to accurately detect NRWIs. The technological characteristics and the physical context of CRNS make it currently to the most promising candidate to overcome the scale gap in NRWIs monitoring in the desert. If proved successful, this will be a novel and relevant tool for monitoring the water balance of arid and semi-arid areas, which is critical for the understanding of ecosystem dynamics, especially where water is a limiting resource.
--In collaboration with Martin Schrön and Steffen Zacharias, Helmholtz Centre for Environmental Research GmbH - UFZ, Germany
Distinguish between dew formation and water vapor adsorption with hyperspectral thermal imaging
Generally, the combination of atmospheric water vapor concentration and temperature close to the soil surface and the surface temperature itself determine if dew formation or water vapor adsorption will occur. Dew occurs when the surface temperature is lower than or equal to the dew-point temperature, causing condensation of water vapor from the air when contacting the cold surface. Water vapor adsorption occurs when the surface temperature is higher that the dew-point temperature and the relative humidity of the soil pores is lower than the relative humidity of the air. Both dew formation and water vapor adsorption are common phenomena in the Negev desert. While previous work provides some quantification of these processes, it is limited in both the temporal and the spatial extent. The ultimate goal of this research is to quantify dew formation and water vapor adsorption at local to regional scale. Hyperspectral thermal images provide means for monitoring both the surface temperature and emissivity. As emissivity is a function of soil water content, the water content can be inversely be derived from these images. Together with the surface temperature that distinguishes between dew formation and water vapor adsorption, hyperspectral thermal images can be utilized to map these processes.
Generally, the combination of atmospheric water vapor concentration and temperature close to the soil surface and the surface temperature itself determine if dew formation or water vapor adsorption will occur. Dew occurs when the surface temperature is lower than or equal to the dew-point temperature, causing condensation of water vapor from the air when contacting the cold surface. Water vapor adsorption occurs when the surface temperature is higher that the dew-point temperature and the relative humidity of the soil pores is lower than the relative humidity of the air. Both dew formation and water vapor adsorption are common phenomena in the Negev desert. While previous work provides some quantification of these processes, it is limited in both the temporal and the spatial extent. The ultimate goal of this research is to quantify dew formation and water vapor adsorption at local to regional scale. Hyperspectral thermal images provide means for monitoring both the surface temperature and emissivity. As emissivity is a function of soil water content, the water content can be inversely be derived from these images. Together with the surface temperature that distinguishes between dew formation and water vapor adsorption, hyperspectral thermal images can be utilized to map these processes.
Past projects
Improving dew harvesting with multifunctional surfaces
As water scarcity becomes a limiting factor for agricultural production in more and more regions across the world, technologies and practices that can simultaneously increase the amount of available water and reduce water losses become essential for regional communities and nations. Atmospheric water, i.e., water droplets and vapor, is potentially a significant water reservoir. In the form of fog, its utility has been widely explored in coastal areas. Fog is a ground-touching cloud that has been proved to add a worthy amount of water for various uses. Dew, on the other hand, is based on phase change heat transfer when surface temperature is lower than dew point, thus the amount of water involved, is typically much smaller in nature. A specifically designed surface can therefore increase the amount of dew formation in addition to fog capture, by allowing the utilization of atmospheric water towards increasing the amount of available water. For agricultural applications, there must be ways to channel this added water, as well as any other source of precipitation, especially rainfall, into the soil as fast as possible, to avoid evaporative losses. Ideally, such a material will increase the amount of available water and prevent water losses in many regions where water scarcity is a severe social problem affecting human life.
--In collaboration with Neelesh A. Patankar and Kyoo-Chul (Kenneth) Park, Northwestern University, Chicago, USA; Stuart J. Rowan and Chong Liu, University of Chicago, Chicago, USA; and Naftali Lazarovitch, Ben-Gurion University of the Negev, Israel
As water scarcity becomes a limiting factor for agricultural production in more and more regions across the world, technologies and practices that can simultaneously increase the amount of available water and reduce water losses become essential for regional communities and nations. Atmospheric water, i.e., water droplets and vapor, is potentially a significant water reservoir. In the form of fog, its utility has been widely explored in coastal areas. Fog is a ground-touching cloud that has been proved to add a worthy amount of water for various uses. Dew, on the other hand, is based on phase change heat transfer when surface temperature is lower than dew point, thus the amount of water involved, is typically much smaller in nature. A specifically designed surface can therefore increase the amount of dew formation in addition to fog capture, by allowing the utilization of atmospheric water towards increasing the amount of available water. For agricultural applications, there must be ways to channel this added water, as well as any other source of precipitation, especially rainfall, into the soil as fast as possible, to avoid evaporative losses. Ideally, such a material will increase the amount of available water and prevent water losses in many regions where water scarcity is a severe social problem affecting human life.
--In collaboration with Neelesh A. Patankar and Kyoo-Chul (Kenneth) Park, Northwestern University, Chicago, USA; Stuart J. Rowan and Chong Liu, University of Chicago, Chicago, USA; and Naftali Lazarovitch, Ben-Gurion University of the Negev, Israel
Nighttime latent heat fluxes in the Negev desert
The ‘greenhouse effect’ and global warming is induced by emission of greenhouse gases (mainly carbon dioxide, CO2, methane, CH4, and nitrous oxide, N2O). These gases are produced (or consumed) as a result of microbial processes in the soil, and the exchange rate between the soil and the atmosphere depends heavily on soil physical properties (e.g., diffusivity and conductivity) and conditions (mainly soil temperature and water content).
Traditionally, it has been assumed that emission rates of greenhouse gases are higher after rain events than during dry periods. In dryland ecosystems, rainfall is typically scarce, and soil nutrients are poor. Nevertheless, there is evidence showing that high soils emission rates of greenhouse gases occurs even at gravimetric soil moistures as low as 1%. Further indications point to dew formation and water vapor adsorption as drivers of trace gas release. The overall aim of this research is to quantify latent heat flux over bare soil in a desert area during the dry season. To achieve this goal, state-of-the-art measurement methods (e.g., eddy covariance and scintillometry) are employed and their capability to detect the small nighttime fluxes involved in dew formation and water vapor adsorption.
The ‘greenhouse effect’ and global warming is induced by emission of greenhouse gases (mainly carbon dioxide, CO2, methane, CH4, and nitrous oxide, N2O). These gases are produced (or consumed) as a result of microbial processes in the soil, and the exchange rate between the soil and the atmosphere depends heavily on soil physical properties (e.g., diffusivity and conductivity) and conditions (mainly soil temperature and water content).
Traditionally, it has been assumed that emission rates of greenhouse gases are higher after rain events than during dry periods. In dryland ecosystems, rainfall is typically scarce, and soil nutrients are poor. Nevertheless, there is evidence showing that high soils emission rates of greenhouse gases occurs even at gravimetric soil moistures as low as 1%. Further indications point to dew formation and water vapor adsorption as drivers of trace gas release. The overall aim of this research is to quantify latent heat flux over bare soil in a desert area during the dry season. To achieve this goal, state-of-the-art measurement methods (e.g., eddy covariance and scintillometry) are employed and their capability to detect the small nighttime fluxes involved in dew formation and water vapor adsorption.
Develop methodology for measuring dew and water vapor adsorption
During nighttime, latent heat fluxes to or from the soil surface are usually very small and so are the absolute amounts of dew formation. The detection of such small fluxes poses serious measurement difficulties. Various methods for measuring dew have been described in the literature and most of them rely on the use of artificial condensing plates with physical properties that are very different from those of soil surfaces. A system that detects the actual dew formation on the soil surface under natural conditions is advantageous and microlysimeters (MLs) appear to be the obvious answer. The objectives of this work were to test the adequacy of microlysimeters to estimate condensation amounts, and to compare these amounts with those measured by a Hiltner dew balance in order to validate the long term data collected using the latter. The results show that for measuring dew, the minimum depth of a microlysimeter should exceed the depth at which the diurnal temperature is constant, which for a dry loess soil in the Negev Desert is 50 cm.
During nighttime, latent heat fluxes to or from the soil surface are usually very small and so are the absolute amounts of dew formation. The detection of such small fluxes poses serious measurement difficulties. Various methods for measuring dew have been described in the literature and most of them rely on the use of artificial condensing plates with physical properties that are very different from those of soil surfaces. A system that detects the actual dew formation on the soil surface under natural conditions is advantageous and microlysimeters (MLs) appear to be the obvious answer. The objectives of this work were to test the adequacy of microlysimeters to estimate condensation amounts, and to compare these amounts with those measured by a Hiltner dew balance in order to validate the long term data collected using the latter. The results show that for measuring dew, the minimum depth of a microlysimeter should exceed the depth at which the diurnal temperature is constant, which for a dry loess soil in the Negev Desert is 50 cm.
Evaporation during the dry season and its role in meso-scale meteorological models
Land surface processes in general, and the energy partitioning at the soil surface in particular, play an important role in global and meso-scale studies. These processes are usually integrated as sub-sets (or sub-models) of global and meso-scale models. Most meso-scale models use parameterization approaches according which the actual evaporation rate is a fraction of the potential evaporation, which depends on the soil water content. This formulation is based on the implicit assumptions that the soil moisture content does not drop below the wilting point and therefore latent heat flux is set to zero when soil moisture content reaches the wilting point. Measurements carried out above a loess soil in the Negev desert, during the dry season, indicated that the water content of the uppermost soil layer reach values which are significantly and systematically lower than the wilting point. Nevertheless, latent heat flux densities, resulting from diurnal processes of water vapor adsorption and evaporation, were monitored throughout the dry season. It is clear, thus, that models that assume that during the dry season there is no latent heat flux over deserts may lead to erroneous results.
Land surface processes in general, and the energy partitioning at the soil surface in particular, play an important role in global and meso-scale studies. These processes are usually integrated as sub-sets (or sub-models) of global and meso-scale models. Most meso-scale models use parameterization approaches according which the actual evaporation rate is a fraction of the potential evaporation, which depends on the soil water content. This formulation is based on the implicit assumptions that the soil moisture content does not drop below the wilting point and therefore latent heat flux is set to zero when soil moisture content reaches the wilting point. Measurements carried out above a loess soil in the Negev desert, during the dry season, indicated that the water content of the uppermost soil layer reach values which are significantly and systematically lower than the wilting point. Nevertheless, latent heat flux densities, resulting from diurnal processes of water vapor adsorption and evaporation, were monitored throughout the dry season. It is clear, thus, that models that assume that during the dry season there is no latent heat flux over deserts may lead to erroneous results.