Abstract
Regions with high productivity of agriculture, such as the Beqaa Plain, Lebanon, often rely on groundwater supplies for irrigation demand. Recent reports have indicated that groundwater consumption in this region has been unsustainable, and quantifying rates of groundwater depletion has remained a challenge. Here, we utilize 15 years of data (June 2002–April 2017) from the Gravity Recovery and Climate Experiment (GRACE) satellite mission to show Total Water Storage (TWS) changes in Lebanon’s Beqaa Plain. We then obtain complimentary information on various hydrologic cycle variables, such as soil moisture storage, snow water equivalent, and canopy water storage from the Global Land Data Assimilation System (GLDAS) model, and surface water data from the largest body of water in this region, the Qaraaoun Reservoir, to disentangle the TWS signal and calculate groundwater storage changes. After combining the information from the remaining hydrologic cycle variables, we determine that the majority of the losses in TWS are due to groundwater depletion in the Beqaa Plain. Results show that the rate of groundwater storage change in the West Beqaa is nearly +0.08 cm/year, in the Rashaya District is −0.01 cm/year, and in the Zahle District the level of depletion is roughly −1.10 cm/year. Results are confirmed using Sentinel-1 interferometric synthetic aperture radar (InSAR) data, which provide high-precision measurements of land subsidence changes caused by intense groundwater usage. Furthermore, data from local monitoring wells are utilized to further showcase the significant drop in groundwater level that is occurring through much of the region. For monitoring groundwater storage changes, our recommendation is to combine various data sources, and in areas where groundwater measurements are lacking, we especially recommend the use of data from remote sensing.
Highlights
During the past few decades, the demanding needs for fresh water resources in various locations of the globe have exceeded the supply that is renewed naturally, and this has impacted agricultural industries, urban areas, and the environment [1,2,3]
The utilization of the techniques presented in this study provide a country like Lebanon, or other regions with a lack of observational data, a framework to assess groundwater storage on the basin scale, where consistent data on water wells is mostly missing and during a time that chaotic, unchecked, and unsustainable groundwater pumping is being exacerbated in the region
For the Zahle District, significant water loss has been observed over the Gravity Recovery and Climate Experiment (GRACE) data record
Summary
During the past few decades, the demanding needs for fresh water resources in various locations of the globe have exceeded the supply that is renewed naturally, and this has impacted agricultural industries, urban areas, and the environment [1,2,3] This is especially the case for semi-arid regions such as the Beqaa Plain in Lebanon. To fulfill the gap in demand for freshwater, a large dependence on groundwater, a convenient fossil resource stored in shallow aquifers below the ground, has occurred in various regions of the world. This is unsustainable, because groundwater recharge that replenishes the system is a slow process compared to the increasing rates of groundwater pumping. With precipitation becoming more variable and droughts more frequent, groundwater pumping
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