A detailed analysis of the SPI variability was conducted targeting nine north western and northeastern meteorological stations in Libya, which has been followed by another thorough analysis of the relationship between such SPI variability... more
A detailed analysis of the SPI variability was conducted targeting nine north western and northeastern meteorological stations in Libya, which has been followed by another thorough analysis of the relationship between such SPI variability and the North Atlantic Oscillation (NAO). A long term precipitation time series spans over the period (1946-2010) has been used along with NAO index data covering the same period of study. The results of the SPI analysis revealed evident distinguish periods of drought and wet years. Stations from Zwara to Benina have experienced a prolonged spell of drought from the beginning of study period up to early eighties, where since then turned to a clear intensified period of wet years onwards. In an opposite manner, the sites of Shahat and Derna started with wet period up to late seventies and shifted to drought afterwards particularly for Shahat station. Interestingly, the long period of drought illustrated at stations from Zwara through Benina seemed favors the negative phase of NAO (NAO-) whereas wet period is associated with positive phase of NAO (NAO+) with some differences between stations. In contrast, Shahat and Derna have responded negatively to NAO in general although for coastal Derna station, fourteen consecutive wet years from 1992-2005 could be attributed to the late impact of positive NAO in that region. The outcomes of this study could indeed benefit in the proactive management plans for the already at risk sectors e.g. agriculture, water resources including groundwater withdraws and water management during severe drought periods.
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The main objective of this study was to analyze rainfall time series from a stretchered region in northeastern Libya focusing on the Mediterranean effective rainy period (Oct.-Mar.). The Mann-Kendall test (non-parametric) was used for... more
The main objective of this study was to analyze rainfall time series from a stretchered region in northeastern Libya focusing on the Mediterranean effective rainy period (Oct.-Mar.). The Mann-Kendall test (non-parametric) was used for detecting potential trends and assessing their significance. For this purpose, rainfall data recorded at four meteorological stations in northeastern Libya (Cyrenaica) are used over the period 1945-2010. All data were tested beforehand for homogeneity in order to be confident that the measurements were taken with the same instruments and at the same locations. Autocorrelation analysis was performed to meet the data randomness requirement for the Mann-Kendall test. For the wet period, statistically significant (at 95% confidence level) increasing and decreasing trends were found at the Ajdabiya and Shahat stations, respectively. Non-significant decreases were detected at the Benina Airport and Derna stations. A brief comparison has been made between the outcomes of this study and a previous relevant study showed an opposite direction of precipitation trend between northeastern and northwestern regions.
Steady-state three-dimensional model using the PMWIN MODFLOW was developed to simulate sub-regional groundwater flow during the pre-development period in response to natural stresses within Al Kufrah area. In order to simulate the... more
Steady-state three-dimensional model using the PMWIN MODFLOW was developed to simulate sub-regional groundwater flow during the pre-development period in response to natural stresses within Al Kufrah area. In order to simulate the interactions among aquifer behavior in response to groundwater pumpage and contaminant transport during the post-development period. The entire simulated thickness of 300 meters was modeled as three hydraulically connected horizontal layers. Each layer consists of 181 rows and 181 columns with grid spacing of 500 m by 500 m which covers an area of 8100 km 2. General Head Boundary (GHB) was assigned to the southern and eastern-northeastern nodes to simulate groundwater inflow and outflow within the simulated area. Evapotranspiration from the upper layer was fixed to the model upper layer only. The hydraulic conductivity, the vertical conductance and the boundary conditions were adjusted by trial and error procedures until satisfactory matching between the observed and the simulated hydraulic head configurations in each layer were achieved. The model-calculated hydraulic heads were statistically tested against the measured pre-development hydraulic heads in 32 observation wells. They gave a root mean square error (RMSE) of 1.0854 m over the observed hydraulic heads that ranges from 364.5m to 396.4m for layer 1, and RMSE error of 1.1914m over a range of 34.16m between the lowest and the highest observed head in layer 3. This indicates the ability of the model to simulate the pre-development stage with confidence. Model water budget shows that, the primary source of groundwater recharge entered from the southern boundary (2.56x10 4 m 3 /day). Groundwater naturally discharges through the eastern-northeastern boundary (2.29x10 4 m 3 /day) and due to evapotranspiration at the low land areas (2.63x10 3 m 3 /day). The net vertical exchanges between layers 1 and 2 and between layers 2 and 3 are 5.43x10 2 m 3 /day and 6.5x10 2 m 3 /day respectively.
This study is based on historical total annual rainfall recorded at eleven meteorological stations located in the northwestern part of Libya. The data were analyzed to study long term temporal trends on annual scale. The rainfall time... more
This study is based on historical total annual rainfall recorded at eleven meteorological stations located in the northwestern part of Libya. The data were analyzed to study long term temporal trends on annual scale. The rainfall time series data were tested for homogeneity and randomness in order to be confident that the measurements were taken at the time with the same instruments and location. After testing, Mann–Kendall test was applied to detect the trends in rainfall data. Theil-Sen's slope estimator test was used for finding the magnitude of change over a time period. The results of Mann–Kendall test detected statistically significant trends of increasing and decreasing rainfall in two out of eleven stations at 95% and 99% confidence levels, namely Sirt and Tripoli Airport stations. During the study period of observation, Sen's Slope and change percentage were estimated as 0.829 mm/year rainfall increase (36.88 %) in Sirt station and-0.686 mm/year (20.04 %) rainfall decrease in Tripoli Airport station.
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Abstract: Groundwater samples from the shallow aquifer in Alassa area, northwestern Libya were studied for their chemical properties. Hydrogeochemical characteristics were evaluated as well as ionic ratios (HCO3-/Cl-, Na+/Cl-, Ca+2/Cl-,... more
Abstract: Groundwater samples from the shallow aquifer in Alassa area, northwestern Libya were studied for their chemical properties. Hydrogeochemical characteristics were evaluated as well as ionic ratios (HCO3-/Cl-, Na+/Cl-, Ca+2/Cl-, Ca+2/SO4-2) to explain the distribution of the facies and the source of existing salinity. The study area shows that there is a mixture of different types of water with variable concentrations of major ions, resulted from salt water intrusion as well as dissolution of evaporates in the aquifer3 bearing water with limited influence of upward leakage. Chloride is found the dominant in the groundwater of the shallow aquifer in the study area caused by sea water encroachment at the coastal area as well as dissolution of halite pockets within the evaporate deposits at the southwestern part of the study area. The quality of groundwater and the processes that control the concentration of major constituents is very necessary to secure adequate water demand. The results of such studies will enable establishing and improving management of the groundwater resources of the area.
Keywords: Hydrochemistry, coastal aquifer, NW Libya
Keywords: Hydrochemistry, coastal aquifer, NW Libya