Spatiotemporal dynamics of water table depth in Southwest China (1958–2015) under complex hydrogeological settings

Groundwater provides an essential buffer against hydroclimatic variability in monsoon-influenced regions, yet its long-term dynamics and interactions with human activities remain poorly constrained in complex hydrogeological settings such as Southwest China (SWC). This study integrates outputs from the high-resolution PCRaster Global Water Balance model (PCR-GLOBWB) with spatial statistics to examine temporal evolution, spatial heterogeneity, and anthropogenic influences on Water Table Depth (WTD) from 1958 to 2015. Results reveal a persistent long-term rise in groundwater levels (i.e., a decline in WTD) at a Sen's slope of –0.0285 m/y, with episodic drawdowns during drought years and only partial recovery in subsequent wet periods. Seasonal oscillations remain pronounced, with the shallowest water tables occurring in late summer and the deepest in spring, although long-term depletion suggests that natural recharge is insufficient to balance cumulative extraction. Shallow aquifers (<1 m) are closely coupled with precipitation–evapotranspiration variability, while deeper systems (>5 m) are increasingly buffered and display inverse relationships, reflecting delayed recharge processes. Spatial patterns demonstrate strong heterogeneity across climate zones, geomorphic units, land cover types, and aquifer types: Shallow groundwater is concentrated in semi-arid climates, lowland plains, and urban areas, whereas mountainous regions, undeveloped land, and discontinuous carbonate aquifers sustain deeper and more variable WTDs. Anthropogenic stress further modulates these distributions, with bivariate LISA analysis identifying High–High clusters (intensive human modification and deep water tables) in the Chengdu Plain and central Yunnan, and Low–Low clusters in sparsely populated western highlands. A groundwater protection zoning framework derived from these results highlights shallow aquifers under intensive stress as priority areas for monitoring and regulation. These findings demonstrate the coupled influence of climate and human activity on groundwater variability and provide a practical basis for regionally targeted management strategies to enhance groundwater sustainability in SWC.