West Jerusalem, Israel
West Jerusalem, Israel

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Dvory N.Z.,Ben - Gurion University of the Negev | Dvory N.Z.,Etgar A. Engineering Ltd. | Livshitz Y.,Israel Hydrological Service | Kuznetsov M.,Ben - Gurion University of the Negev | And 2 more authors.
Journal of Hydrology | Year: 2016

Groundwater recharge in fractured karstic aquifers is particularly difficult to quantify due to the rock mass's heterogeneity and complexity that include preferential flow paths along karst conduits. The present study's major goals were to assess how the changes in lithology, as well as the fractured karst systems, influence the flow mechanism in the unsaturated zone, and to define the spatial variation of the groundwater recharge at local scale. The study area is located within the fractured carbonate Western Mountain aquifer (Yarkon-Taninim), west of the city of Jerusalem at the Ein Karem (EK) production well field. Field monitoring included groundwater level observations in nine locations in the study area during years 1990-2014. The measured groundwater level series were analyzed with the aid of one-dimensional, dual permeability numerical model of water flow in variably saturated fractured-porous media, which was calibrated and used to estimate groundwater recharge at nine locations. The recharge values exhibit significant spatial and temporal variation with mean and standard deviation values of 216 and 113 mm/year, respectively. Based on simulations, relationships were established between precipitation and groundwater recharge in each of the nine studied sites and compared with similar ones obtained in earlier regional studies. Simulations show that fast and slow flow paths conditions also influence annual cumulative groundwater recharge dynamic. In areas where fast flow paths exist, most of the groundwater recharge occurs during the rainy season (60-80% from the total recharge for the tested years), while in locations with slow flow path conditions the recharge rate stays relatively constant with a close to linear pattern and continues during summer. © 2016 Elsevier B.V.

Helman D.,Bar - Ilan University | Givati A.,Israel Hydrological Service | Lensky I.M.,Bar - Ilan University
Atmospheric Chemistry and Physics | Year: 2015

We present a model to retrieve actual evapotranspiration (ET) from satellites' vegetation indices (Parameterization of Vegetation Indices for ET estimation model, or PaVI-E) for the eastern Mediterranean (EM) at a spatial resolution of 250 m. The model is based on the empirical relationship between satellites' vegetation indices (normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI) from MODIS) and total annual ET (ETAnnual) estimated at 16 FLUXNET sites, representing a wide range of plant functional types and ETAnnual. Empirical relationships were first examined separately for (a) annual vegetation systems (i.e. croplands and grasslands) and (b) systems with combined annual and perennial vegetation (i.e. woodlands, forests, savannah and shrublands). Vegetation indices explained most of the variance in ETAnnual in those systems (71 % for annuals, and 88 % for combined annual and perennial systems), while adding land surface temperature data in a multiple-variable regression and a modified version of the Temperature and Greenness model did not result in better correlations (p > 0.1). After establishing empirical relationships, PaVI-E was used to retrieve ETAnnual for the EM from 2000 to 2014. Models' estimates were highly correlated (R = 0.92, p < 0.01) with ETAnnual calculated from water catchment balances along rainfall gradient of the EM. They were also comparable to the coarser-resolution ET products of the Land Surface Analysis Satellite Applications Facility (LSA-SAF MSG ETa, 3.1 km) and MODIS (MOD16, 1 km) at 148 EM basins with R of 0.75 and 0.77 and relative biases of 5.2 and -5.2 %, respectively (p < 0.001 for both). In the absence of high-resolution (< 1 km) ET models for the EM the proposed model is expected to contribute to the hydrological study of this region, assisting in water resource management, which is one of the most valuable resources of this region. © Author(s) 2015.

Ben-Asher J.,Ben - Gurion University of the Negev | Alpert P.,Tel Aviv University | Ben-Zvi A.,Israel Hydrological Service
Water Resources Research | Year: 2010

The purpose here is to reexamine the ecological importance of dew in arid and semiarid regions with a focus on the eastern Mediterranean area. This reevaluation is of particular importance under the controversial perspective that dew is insufficient as a source of water for plants but is sufficient to promote the spread of plant diseases. Adana, Turkey, was selected as an appropriate semiarid test ground with well-documented meteorological data and a newly developed photosynthesis and transpiration rate monitor (PTM), which was used to detect the response of transpiration and photosynthesis to the presence of dew on the leaves. A convolution theoretical model was used to simulate no-dew days; simultaneously, PTM measurements were used to obtain actual situations with dew. Contrary to expectations, we detected separate, early peaks of photosynthesis and late peaks of transpiration, leading to an average ratio of about 2:1 units of water use efficiency (WUE) for dew-affected versus no-dew conditions. The impressive performance of the dew-affected WUE was explained by a synergy between (1) low transpiration during dew-affected morning hours and (2) high CO2 gradient toward the canopy. The first resulted from dew formation that created a humid environment in the near vicinity of the leaf followed by a low leaf to air vapor pressure deficit, which minimized transpiration. The second resulted from night respiration that induced a high CO2 gradient from the air toward the canopy. This synergy resulted in intensive carbon intake at a low water cost and explained the ecological importance of dew. Copyright © 2010 by the American Geophysical Union.

Rostkier-Edelstein D.,Israel Institute for Biological Research | Kunin P.,Life science Research Israel | Kunin P.,Tel Aviv University | Hopson T.M.,U.S. National Center for Atmospheric Research | And 2 more authors.
International Journal of Climatology | Year: 2016

Careful planning of the use of water resources is critical in the semi-arid eastern Mediterranean region. The relevant areas are characterized by complex terrain and coastlines, and exhibit large spatial variability in seasonal precipitation. Global seasonal forecasts provide only partial information of the precipitation as a result of their coarse spatial resolution. We present two statistical downscaling methods of global forecasts, both identifying past-analogue synoptic-weather patterns and their connection to precipitation at specific stations. The first method utilizes a classification of the large-scale weather patterns into regimes, and the other identifies the closest past analogues directly without grouping the weather events. The validation of the algorithms using NCEP/NCAR reanalyses and past precipitation observations at 18 stations shows that both methods provide good skill in predicting mean precipitation amounts and quantiles of the precipitation distribution, and in reproducing the observed inter-annual and spatial variability. Both methods show good correlations between predicted and observed precipitation amounts (∼0.8), and the downscaled precipitation reproduces the observed differences between the stations, which are not available in the coarse global models. Based on these results, we downscaled the operational global-seasonal forecasts issued by the NCEP CFS1.0 ensemble. This approach could also have utility in climate change scenario downscaling. © 2016 Royal Meteorological Society.

This article paves a way for assessing flood risk by the use of two-parameter distributions, for the intervals between threshold exceedences rather than by the traditional exponential distribution. In a case study, the apparent properties of intervals between exceedences of runoff events differ from those anticipated for exponentially distributed series. A procedure is proposed to relate two statistical parameters of the intervals to threshold discharges. It considers partial duration series (PDS) with thresholds equal to all high enough observed discharges. To avoid unnecessary assumptions on the behaviour of those parameters and effects of dependence between parameters for different PDS, a non-parametric trend-free pre-whitened scheme is applied. It leads to power-law relationships between a discharge and the mean and standard deviation of the intervals between its exceedences. Predicted mean inter-exceedence intervals, for the highest observed discharges at the stations, are closer to the observational periods than those predicted by GEV distributions fitted to AMS, and by GP distributions to fitted PDS. In the present case, the latter predictions are longer than the observational periods whereas some of the predicted mean inter-exceedences are shorter than the corresponding observational periods and some others are longer. © 2010 IAHS Press.

Rostkier-Edelstein D.,Israel Institute for Biological Research | Liu Y.,U.S. National Center for Atmospheric Research | Wu W.,U.S. National Center for Atmospheric Research | Kunin P.,Life science Research Israel | And 2 more authors.
International Journal of Climatology | Year: 2014

This study demonstrates the capability of the Weather Research and Forecasting (WRF) model with four-dimensional data assimilation (WRF-FDDA) to produce a high-resolution climatography of seasonal precipitation over Israel and the surrounding areas. The system was used to dynamically downscale global Climate Forecast System (CFS) reanalysis with continuous assimilation of conventional and unconventional observations. Precipitation seasons (December-January-February) in 7years, including two extreme dry and wet seasons observed in the past decades, were generated at 2-km spatial resolution. Verification against rain-gauge observations shows that the WRF-FDDA system effectively reproduces the spatial and inter-annual variability, as well as the timing, intensity, and length of wet and dry spells. The best agreement between model and observations was obtained at areas dominated by complex terrain, illustrating the benefit of the high-resolution lower boundary forcing in the dynamical downscaling process. In contrast, some biases were observed over coastal-flat terrain. The model was able to reproduce some of the extreme events, but exhibited limitations in the case of rare events. This specific discrepancy between the model and observations suggests that further fine tuning and different model configurations may be needed to correctly simulate extreme events. The use of an objective weather-regimes verification procedure reveals the skill of the climatography for different types of extra-tropical cyclones: while biases are larger at coastal-flat areas under shallow-cyclonic conditions, deep-cyclonic conditions lead to more significant biases in complex terrain regions. The weather-regimes dependent information may be used for further calibration of the downscaled precipitation. © 2013 Royal Meteorological Society.

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