Groundwater resources are essential for agricultural sustainability in semi-arid regions, yet continuous empirical observations of deep aquifer dynamics remain scarce. This study addresses this empirical gap by presenting the first multi-year, high-frequency telemetry record of groundwater-level, thermal, and Total Dissolved Solids (TDS) dynamics from a dedicated 400 m unpumped observation borehole in Kfardane, Northern Bekaa Valley, Lebanon. A total of 2998 piezometric observations (6-hour logging intervals) collected between April 2024, and August 2026 were analyzed alongside daily precipitation, air temperature, and in-situ TDS data across two contrasting hydrological cycles following a severe drought. Results reveal pronounced seasonal drawdown driven by regional agricultural abstraction, reaching an absolute maximum water-table depth of 233.0 m b.g.l. in July 2025 following an anomalously dry wet season (126 mm rainfall). Conversely, a wetter 2025-2026 winter (311 mm precipitation) generated a robust 17.0 m hydraulic head recovery by April 2026 (216 m b.g.l.), buffering the aquifer against extreme stress during the subsequent 2026 irrigation season (summer drawdown reaching 227.2 m b.g.l.). Subsurface temperature remained stable overall (15.8？C - 16.4？C) despite surface air fluctuations exceeding 40？C. Transient downhole cooling events (ΔT = ？0.51？C) coincided with rapid, concurrent drops in TDS (ΔTDS = ？64.8 ppm) following peak winter precipitation and rapid mountain snowmelt. Overall, the findings demonstrate that seasonal groundwater stress in the deep Bekaa aquifer is governed by the interaction of irrigation pressure, precipitation variability, and multi-year antecedent storage memory (highlighting the importance of telemetry).
References
[1]
Aeschbach-Hertig, W. and Gleeson, T. (2012) Regional Strategies for the Accelerating Global Problem of Groundwater Depletion. Nature Geoscience, 5, 853-861. https://doi.org/10.1038/ngeo1617
[2]
Gleeson, T., Wada, Y., Bierkens, M.F.P. and van Beek, L.P.H. (2012) Water Balance of Global Aquifers Revealed by Groundwater Footprint. Nature, 488, 197-200. https://doi.org/10.1038/nature11295
[3]
Konikow, L.F. and Kendy, E. (2005) Groundwater Depletion: A Global Problem. Hydrogeology Journal, 13, 317-320. https://doi.org/10.1007/s10040-004-0411-8
[4]
Wada, Y., van Beek, L.P.H., van Kempen, C.M., Reckman, J.W.T.M., Vasak, S. and Bierkens, M.F.P. (2010) Global Depletion of Groundwater Resources. Geophysical Research Letters, 37, L20402. https://doi.org/10.1029/2010gl044571
[5]
Taylor, R.G., Scanlon, B., D？ll, P., Rodell, M., van Beek, R., Wada, Y., et al. (2013) Ground Water and Climate Change. Nature Climate Change, 3, 322-329. https://doi.org/10.1038/nclimate1744
[6]
Scanlon, B.R., Jolly, I., Sophocleous, M. and Zhang, L. (2007) Global Impacts of Conversions from Natural to Agricultural Ecosystems on Water Resources: Quantity Versus Quality. Water Resources Research, 43, W03437.
[7]
Shaban, A. (2009) Indicators and Aspects of Hydrological Drought in Lebanon. Water Resources Management, 23, 1875-1891.
[8]
Mazzilli, N., Bouchaou, L., Jourde, H., Leduc, C. and Chalikakis, K. (2019) Karst Aquifers in the Mediterranean Region: Hydrogeological Functioning and Vulnerability to Climate Change. Journal of Hydrology: Regional Studies, 24, Article 100612.
[9]
Immerzeel, W.W., Lutz, A.F., Andrade, M., Bahl, A., Biemans, H., Bolch, T., et al. (2020) Importance and Vulnerability of the World’s Water Towers. Nature, 577, 364-369. https://doi.org/10.1038/s41586-019-1822-y
[10]
Jomaa, I. and Shaban, A. (2018) Improving Water-Use Efficiency and Productivity in the Litani River Basin. In: Shaban, A. and Hamzé, M., Eds., The Litani River, Lebanon: An Assessment and Current Challenges, Springer International Publishing, 145-160.
[11]
El-Fadel, M., Zeinati, M. and Jamali, D. (2000) Water Resources in Lebanon: Characterization, Water Balance and Constraints. International Journal of Water Resources Development, 16, 615-638. https://doi.org/10.1080/713672540
[12]
Shaban, A., Khawlie, M. and Abdallah, C. (2006) Use of Remote Sensing and GIS to Determine Recharge Potential Zones: The Case of Occidental Lebanon. Hydrogeology Journal, 14, 433-443.
[13]
Darwish, T., Atallah, T., Francis, R. and Saab, C. (2011) Impact of Agriculture on Groundwater Resources in the Bekaa Valley, Lebanon. Lebanese Science Journal, 12, 113-123.
[14]
Jaafar, H.H. and Ahmad, F.A. (2020) Time Series Trends of Landsat-Based ET Using Automated Calibration in METRIC and SEBAL: The Bekaa Valley, Lebanon. Remote Sensing of Environment, 238, Article 111034. https://doi.org/10.1016/j.rse.2018.12.033
[15]
Jomaa, I., Sbeih, M.S. and Jaubert, R. (2015) Sharp Expansion of Intensive Groundwater Irrigation, Semi-Arid Environment at the Northern Bekaa Valley Lebanon. Natural Resources, 6, 381-390. https://doi.org/10.4236/nr.2015.66036
[16]
Voss, K.A., Famiglietti, J.S., Lo, M., de Linage, C., Rodell, M. and Swenson, S.C. (2013) Groundwater Depletion in the Middle East from GRACE with Implications for Transboundary Water Management in the Tigris-Euphrates-Western Iran Region. Water Resources Research, 49, 904-914. https://doi.org/10.1002/wrcr.20078
[17]
Massoud, E.C., Liu, Z., Shaban, A. and Hage, M. (2021) Groundwater Depletion Signals in the Beqaa Plain, Lebanon: Evidence from GRACE and Sentinel-1 Data. Remote Sensing, 13, Article 915. https://doi.org/10.3390/rs13050915
[18]
Post, V.E.A. and von Asmuth, J.R. (2013) Review: Hydraulic Head Measurements—New Technologies, Classic Pitfalls. Hydrogeology Journal, 21, 737-750. https://doi.org/10.1007/s10040-013-0969-0
[19]
Bakalowicz, M. (2005) Karst Groundwater: A Challenge for New Resources. Hydrogeology Journal, 13, 148-160. https://doi.org/10.1007/s10040-004-0402-9
[20]
Kiraly, L. (2002) Karst Site Characterization: Overview of Various Approaches. Environmental Geology, 42, 549-559.
[21]
Sauter, M. (1992) Quantification and Forecasting of Regional Groundwater Flow and Transport in a Karst Aquifer (Gallusquelle, Malm, SW Germany) (Tübinger Geowissenschaftliche Arbeiten, Reihe C, Nr. 11). Institut für Geologie und Pal？ontologie der Universit？t Tübingen.
[22]
Ford, D. and Williams, P. (2007) Karst Hydrogeology and Geomorphology. Wiley. https://doi.org/10.1002/9781118684986
[23]
Hartmann, A., Goldscheider, N., Wagener, T., Lange, J. and Weiler, M. (2014) Karst Water Resources in a Changing World: Review of Hydrological Modeling Approaches. Reviews of Geophysics, 52, 218-242. https://doi.org/10.1002/2013rg000443
[24]
Allocca, V., Marfella, L., De Vita, P. and Celico, F. (2021) High-Frequency Monitoring of Groundwater Levels and Head Response Analysis in Karst Aquifers. Journal of Hydrology, 598, Article 126233.
[25]
Rau, G.C., Halloran, L.J.S., Cuthbert, M.O., Andersen, M.S., McCallum, M.G. and Acworth, R.I. (2019) Characterising Dynamic Aquifer Processes Using Water Table Fluctuations: A Review. Earth-Science Reviews, 193, 114-134.
[26]
Anderson, M.P. (2005) Heat as a Ground Water Tracer. Groundwater, 43, 951-968. https://doi.org/10.1111/j.1745-6584.2005.00052.x
[27]
Saar, M.O. (2011) Review: Geothermal Heat as a Tracer of Large-Scale Groundwater Flow and as a Means to Determine Permeability Fields. Hydrogeology Journal, 19, 31-52.
[28]
Bense, V.F., Kurylyk, B.L., van Breukelen, B.M. and Irvine, D.J. (2016) Computational Benchmark Illustrations of Heat Transport Modeling in Fractured Aquifers. Advances in Water Resources, 93, 4-15.
[29]
Kurylyk, B.L., Irvine, D.J., Carey, S.K., Briggs, M.A., Werkema, D.D. and Bonham, M. (2017) Heat as a Groundwater Tracer in Shallow and Deep Heterogeneous Media: Analytical Solution, Spreadsheet Tool, and Field Applications. Hydrological Processes, 31, 2648-2661. https://doi.org/10.1002/hyp.11216
[30]
Irvine, D.J., Briggs, M.A., Lautz, L.K., Gordon, R.P., McKenzie, J.M. and Kurylyk, B.L. (2017) Using Heat to Characterize Vertical Streamflow Exchanges in Fractured and Heterogeneous Porous Media. Hydrogeology Journal, 25, 521-537.
[31]
Fiorillo, F. (2009) Spring Discharge Analysis Using Recession Curves: A Review. Environmental Earth Sciences, 59, 145-155.
[32]
Goldscheider, N. and Drew, D. (2007) Methods in Karst Hydrogeology. Taylor & Francis.
[33]
Fayad, A., Gascoin, S., Faour, G., López-Moreno, J.I., Drapeau, L., Le Page, M. and Escadafal, R. (2017) Snow Mapping in the Lebanon Mountains Using MODIS Daily Snow Products and Validation with High-Resolution Images. Hydrological Sciences Journal, 62, 374-396.
[34]
Musselman, K.N., Clark, M.P., Liu, C., Ikeda, K. and Rasmussen, R. (2017) Slower Snowmelt in a Warmer World. Nature Climate Change, 7, 214-219. https://doi.org/10.1038/nclimate3225
