USE OF GRACE AND LSMS OUTPUTS FOR THE ASSESSMENT AND SUSTAINABLE UTILIZATION OF THE MEGA AQUIFER SYSTEM OVER THE ARABIAN PENINSULA

The Mega Aquifer System (MAS) is one of the largest multi-layered aquifers (Wajid, Saq, Tabuk, Minjur, Dhruma, Biyadh, Wasia, Aruma, Umm Er Radhuma, Dammam, and Neogene) worldwide that covers extensive areas (1.7×10⁶ km²) in the Kingdom of Saudi Arabia, Yemen, Oman, Emirates, Qatar, Kuwait, and Jordan with thicknesses ranging from 1.7 to 2 km. The MAS was largely recharged under previous wet climatic conditions, yet is still receiving modest local modern recharge at present. In the 1980s the Kingdom of Saudi Arabia adopted an aggressive program for groundwater extraction from the Lower MAS (LMAS) to reclaim the deserts in northern and central Arabia; between years 1984 and 2005, groundwater extraction in these areas increased from 2.0 to 8.7 BCM and the cultivated lands increased from 227 × 10³ to 526 × 10³ hectares and the groundwater levels declined by 1.5 to 3.5 m/yr. An integrated approach (remote sensing, field, GIS) was adopted to accomplish the following: (1) investigate temporal variations in terrestrial water storage (TWS) over the Lower MAS (LMAS) using Gravity Recovery and Climate Experiment (GRACE) recently released (release 05; RL05), high resolution (grid size: 0.5° x 0.5°), monthly (04/2002-06/2016), mass concentrations (mascon) solutions; (2) generate a GIS database to host all relevant data and derived products (remote sensing, geology, GPS, groundwater extraction rates, and water levels, etc.) and to conduct spatial correlations of these spatial and temporal datasets; (3) assess aquifer depletion rates over the LMAS using temporal GRACE solutions and outputs (soil moisture) of the Global Land Data Assimilation System (GLDAS) model, and (4) identify extraction scenarios to attain sustainable utilization. Findings include: (1) the secular trends for the GRACE-derived TWS and GWS over the LMAS were estimated at −9.1 ± 1.3 mm/yr (-4.6 ± 0.5 km³/yr) and −7.8 ± 1.3 mm/yr (-3.7 ± 0.6 km³/yr), respectively, (2) sustainable extraction from the LMAS could be attained by reducing groundwater extraction by 3.5 to 4 km³/yr, and (3) our findings provide replicable and cost-effective methodologies for optimum utilization of fossil aquifers and for minimizing deformational effects associated with their utilization.