Water is crucial for achieving the United Nations’ 2030 Sustainable Development Goals (SDGs), particularly in arid climate regions like the Arabian Peninsula (AP). Terrestrial water storage (TWS) generally serves as the fundamental indicator of water resources availability, which is a key component of water security. Although previous studies have investigated historical variability in TWS, its future changes have received less attention. Employing GRACE satellite data combined with global hydrological (GHMs) and land surface models (LSMs), this study analyzed alterations in TWS throughout the AP under low (RCP2.6) and medium–high (RCP6.0) greenhouse gas concentration scenarios during the mid (2030–2059) and late (2070–2099) future periods. Significant decreases in TWS are predicted for southeastern Saudi Arabia and eastern Yemen, while northern areas, including Kuwait, are expected to experience increases. The rate of TWS decline is projected to be more apparent in the late twenty-first century and under RCP6.0. These insights play a significant role in achieving water security in the AP, thereby contributing to global economic, social, and environmental sustainability.