In an arid environment, especially in sandy areas where surface runoff is of no practical importance in the hydrological budget, it is rainfall, dewfall and evapotranspiration that become the most important variables....In an arid environment, especially in sandy areas where surface runoff is of no practical importance in the hydrological budget, it is rainfall, dewfall and evapotranspiration that become the most important variables. To assess actual evapotranspiration, several methods （flux-gradient, BREB, eddy correlation） were applied to data from the Nizzana experimental site in the northwestern Negev Desert. Additionally, a model specifically designed for arid environments is introduced in this paper. This zero plane model shows the most reasonable results compared with the other methods, which overestimate evapotranspiration to a large degree. It is shown that plant transpiration is the dominant process in total evapotranspiration while advective processes do not play a major role in the near-ground boundary layer, although the study area is influenced by a sea breeze. Actual transpiration ofArtemisia monosperma was measured in a field experiment to validate the calculated evapotranspiration. The vegetation contributed 41% of the calculated total evapotranspiration in a single month.展开更多
Arid and semi-arid regions are characterized by low rainfall and high potential evaporative demand. Here, water is the major limiting factor for plant growth and productivity. Soil and surface hydrology properties （e...Arid and semi-arid regions are characterized by low rainfall and high potential evaporative demand. Here, water is the major limiting factor for plant growth and productivity. Soil and surface hydrology properties （e.g. field capacity, infikration rates） effectively control the water re-distribution in the ecosystem, a fact that is aggravated in arid environments. Information of the spatial and temporal accessibility of soil water in desert ecosystems is limited. The purpose of the studies is the application of plant water potential to estimate the spatial and temporal variations of soil water availability in different arid ecosystems of the Negev （Israel） and southern Morocco. As model plants the evergreen shrubs Retama raetam, Thymelaea hirsuta and trees （Acacia tortilis） were chosen. Seasonal and spatial variations of the pre-dawn water potential （ψpd） were examined as diagnostic tool to determine water availability on the landscape level. The seasonal differences in the pre-dawn water potential were less pronounced on the dune compared to the interdune. This showed a better water availability on the dune slope. Also in the investigated wadis systems spatial differences of the water potential could be detected and related to the vegetation pattern.展开更多
An important task in seismic hazard assessment is the estimation of intensity and frequency of rare strong seismic shaking, in particular, the long-term peak ground velocity values(PGVs). A recently proposed method is...An important task in seismic hazard assessment is the estimation of intensity and frequency of rare strong seismic shaking, in particular, the long-term peak ground velocity values(PGVs). A recently proposed method is suitable for simply estimating PGVs based on the examination of the magnitude of displacements of rock blocks. The effectiveness of this method is demonstrated by results of studies on the source zones of two large earthquakes and a vicinity of one strong explosion. In this study, the method is applied to the examination of archeoseismological data from the ancient Rehovot-ba-Negev city and other ancient cities from the Negev desert(in Southern Israel) where numerous evidences of presumable seismic damage were found earlier. The cities and also a sophisticated irrigation system within the region, which existed in the Negev desert, were abandoned however in the middle of the seventh century. The abandonment could be caused by a combined effect, from not only the cessation of the state support from Byzantium as a result of the Arab conquest but also the severe destruction from the strong earthquake that hit the area at that time. The intensities of the seismic events that hit the cities were estimated earlier, which are within the range of 8 e9. Our estimates indicate that the PGV values are about 1.5 m/s. Hence, the magnitude of the causative earthquake could be in the range M z 6.5 e7.5, and the location of the epicenter might be at a distance of a few dozens of kilometers from the ancient Rehovot-ba-Negev city, while the other variants associated with the earthquake seem to be less probable.展开更多
Global warming and climate change are the most important ecological issues of our time. The most well-known factor in this phenomenon is the redundancy of carbon dioxide in the atmosphere. Over the past 50 years the a...Global warming and climate change are the most important ecological issues of our time. The most well-known factor in this phenomenon is the redundancy of carbon dioxide in the atmosphere. Over the past 50 years the amount of residual CO2 in the atmosphere has risen from 40% to 45%. Reducing CO2 redundancy requires precise knowledge of the gas sources and sinks throughout the atmosphere. Despite having a leading role in residual gas levels of atmosphere, the diagnosis and types of changes of absorbing carbon dioxide are very much in doubt. Atmospheric measurements of CO2 concentrations are highly precise and provide a reliable measure of increase of CO2 in the atmosphere every year but they do not lead to the location of sources and sinks. Studies about understanding CO2 cycles began mainly around 1990 and most of these studies have been focused on non-spatial analysis. By ignoring the spatial effects, an important property such as closeness (adjacent) has been disregarded. The emission sources of gas are stronger than their sink sources i.e., whenever a sink is adjacent to a strong emission source, the measurements will show a massive existence of CO2 gas in that region although there exists a fine CO2?gas sink at below. Using the global measurements of CO2 and applying spatial analysis approach to “Leave One Out” method, our studies reveal the most probable spots of CO2 sources and sinks and that Negev Desert in Middle East is a distinguished CO2 sink region.展开更多
文摘In an arid environment, especially in sandy areas where surface runoff is of no practical importance in the hydrological budget, it is rainfall, dewfall and evapotranspiration that become the most important variables. To assess actual evapotranspiration, several methods （flux-gradient, BREB, eddy correlation） were applied to data from the Nizzana experimental site in the northwestern Negev Desert. Additionally, a model specifically designed for arid environments is introduced in this paper. This zero plane model shows the most reasonable results compared with the other methods, which overestimate evapotranspiration to a large degree. It is shown that plant transpiration is the dominant process in total evapotranspiration while advective processes do not play a major role in the near-ground boundary layer, although the study area is influenced by a sea breeze. Actual transpiration ofArtemisia monosperma was measured in a field experiment to validate the calculated evapotranspiration. The vegetation contributed 41% of the calculated total evapotranspiration in a single month.
文摘Arid and semi-arid regions are characterized by low rainfall and high potential evaporative demand. Here, water is the major limiting factor for plant growth and productivity. Soil and surface hydrology properties （e.g. field capacity, infikration rates） effectively control the water re-distribution in the ecosystem, a fact that is aggravated in arid environments. Information of the spatial and temporal accessibility of soil water in desert ecosystems is limited. The purpose of the studies is the application of plant water potential to estimate the spatial and temporal variations of soil water availability in different arid ecosystems of the Negev （Israel） and southern Morocco. As model plants the evergreen shrubs Retama raetam, Thymelaea hirsuta and trees （Acacia tortilis） were chosen. Seasonal and spatial variations of the pre-dawn water potential （ψpd） were examined as diagnostic tool to determine water availability on the landscape level. The seasonal differences in the pre-dawn water potential were less pronounced on the dune compared to the interdune. This showed a better water availability on the dune slope. Also in the investigated wadis systems spatial differences of the water potential could be detected and related to the vegetation pattern.
基金partial financial support of ISTC grant No. G-2153
文摘An important task in seismic hazard assessment is the estimation of intensity and frequency of rare strong seismic shaking, in particular, the long-term peak ground velocity values(PGVs). A recently proposed method is suitable for simply estimating PGVs based on the examination of the magnitude of displacements of rock blocks. The effectiveness of this method is demonstrated by results of studies on the source zones of two large earthquakes and a vicinity of one strong explosion. In this study, the method is applied to the examination of archeoseismological data from the ancient Rehovot-ba-Negev city and other ancient cities from the Negev desert(in Southern Israel) where numerous evidences of presumable seismic damage were found earlier. The cities and also a sophisticated irrigation system within the region, which existed in the Negev desert, were abandoned however in the middle of the seventh century. The abandonment could be caused by a combined effect, from not only the cessation of the state support from Byzantium as a result of the Arab conquest but also the severe destruction from the strong earthquake that hit the area at that time. The intensities of the seismic events that hit the cities were estimated earlier, which are within the range of 8 e9. Our estimates indicate that the PGV values are about 1.5 m/s. Hence, the magnitude of the causative earthquake could be in the range M z 6.5 e7.5, and the location of the epicenter might be at a distance of a few dozens of kilometers from the ancient Rehovot-ba-Negev city, while the other variants associated with the earthquake seem to be less probable.
文摘Global warming and climate change are the most important ecological issues of our time. The most well-known factor in this phenomenon is the redundancy of carbon dioxide in the atmosphere. Over the past 50 years the amount of residual CO2 in the atmosphere has risen from 40% to 45%. Reducing CO2 redundancy requires precise knowledge of the gas sources and sinks throughout the atmosphere. Despite having a leading role in residual gas levels of atmosphere, the diagnosis and types of changes of absorbing carbon dioxide are very much in doubt. Atmospheric measurements of CO2 concentrations are highly precise and provide a reliable measure of increase of CO2 in the atmosphere every year but they do not lead to the location of sources and sinks. Studies about understanding CO2 cycles began mainly around 1990 and most of these studies have been focused on non-spatial analysis. By ignoring the spatial effects, an important property such as closeness (adjacent) has been disregarded. The emission sources of gas are stronger than their sink sources i.e., whenever a sink is adjacent to a strong emission source, the measurements will show a massive existence of CO2 gas in that region although there exists a fine CO2?gas sink at below. Using the global measurements of CO2 and applying spatial analysis approach to “Leave One Out” method, our studies reveal the most probable spots of CO2 sources and sinks and that Negev Desert in Middle East is a distinguished CO2 sink region.
