Attribution and spatial heterogeneity of groundwater level drivers: Gnangara region in Western Australia

Study Region: The Gnangara region in Western Australia, characterized by a Mediterranean climate with rainfall-dominated recharge, supplies approximately 60% of Perth’s drinking water. Study Focus: This study established spatiotemporal models between GLD and 87 climate and non-climate variables based on a 48-year (1977–2024) dataset from 399 monitoring bores to identify the major drivers of groundwater level differences (GLD) using a progressive statistical framework. New Hydrological Insights for the Region: Results showed: 1) GLD exhibited a significant linear decline (cumulative 0.14 m; multi-year average 0.58 m), driven by long-term drought and sustained abstraction, with a spatial gradient increasing from northwest to southeast, shaped by hydrogeological and climatic gradients. 2) Seasonal climate variables outperformed annual-scale indicators in characterizing groundwater dynamics. Rainfall was the dominant factor influencing GLD, with May-September rainfall positively contributing the most (38.73%), and total rainfall above the 95th percentile threshold contributing 29.87%. June–August potential evaporation (Span68) and mean dry spell length (MeDS) were negatively correlated with GLD, contributing 13.74% and 8.70%, respectively. 3) Among non-climate variables, groundwater abstraction contributed negatively (6.20%), while NDVI had the smallest positive impact (2.76%). Both are scale-dependent, with regional impacts weakened by hydrogeological and climatic heterogeneity. These findings advance groundwater management by supporting targeted strategies: prioritizing seasonal and 95th-percentile rainfall monitoring over annual indicators and implementing permeability-adapted groundwater abstraction management for shallow aquifer dynamics.