Groundwater resources in arid regions like Saudi Arabia are under increasing stress due to over-extraction, climate variability, and limited natural recharge. This study presents an integrated spatiotemporal assessment of groundwater storage (GWS) and vegetation health using satellite-based datasets from 2002 to 2023. Key indicators such as Terrestrial Water Storage (GRACE), precipitation, and the Vegetation Condition Index (VCI) were analyzed alongside a sustainability framework incorporating reliability, resiliency, and vulnerability metrics. Significant groundwater depletion, up to-8 cm/year, was identified in northern and central regions including AlQassim, Riyadh, and Al-Jawf, while southwestern regions like Asir and Jazan exhibited more stable conditions. Approximately 2.15 million km2 was classified as "Extremely Unsustainable," highlighting severe hydrological stress. Bivariate Moran's I and Granger causality analyses revealed strong spatial and temporal links between GWS and vegetation health, particularly in high-priority zones such as Asir and Jazan. These findings stress the urgent need for sustainable groundwater management through artificial recharge, regulated extraction, and efficient irrigation practices to mitigate the impacts of long-term depletion on ecosystems and agriculture.