Low resilience of fractured groundwater systems to climate change and human activities

Groundwater, as an essential and dynamic part of hydrosphere, sustains the water demands and livelihoods in diverse landscapes and ecosystems. Currently, understanding on groundwater responses to climate variability is less addressed in IPCC reports yet important for future projections of water resources and management. Recent studies demonstrate that aridity index and likely hydrogeological setting jointly control the climate resilience of groundwater regionally and globally. However, most of these studies are bounded to quaternary sedimentary aquifers (i.e., North China plain, U.S. plains, Nubia plains) subject to intensive agricultural activities. Compared with quaternary aquifers which is dominated by porous media, groundwater in fractured bedrocks flows faster because of smaller effective porosities. The discharge and recharge processes are therefore expected to be more sensitive to climate variability and anthropogenic activities (i.e., pumping, urbanization, and reclamation) in fractured aquifer, but the underlying mechanism remains unclear, mainly limited by the lack of mature theory to delineate the interplays between fractured aquifers, climatic processes and human forcings, and the scarcity of long-term observation in the fractured bedrock aquifers.

In this study, we leveraged the decadal weekly monitoring (1971-2000) of rainfall, potential evapotranspiration, groundwater table, and stream discharge the headwater catchments dominated by fractured aquifers. with and without major human disturbance. We identified the significantly lower resilience of these fractured groundwater systems to change climates and human activities. By examining the variations and phases of recharge and discharge (baseflow to the river channel), we concluded that the rapid recharge-discharge in the fractured bedrock groundwater might serve as an effective push-pull process to significantly lower the resilience of fractured groundwater systems to climate changes and human disturbance. Topographic metrics i.e., slopes and concavity, are not likely to influence the interplay between fractured groundwater system and climate/human forcings. Our results also highlight the potential teleconnections between the fractured groundwater system and long-term climate changes (i.e., El Niño-Southern Oscillation/Asian summer monsoon/ Asian winter monsoon). This study advances the understanding the role and behaviors of fractured groundwater systems under changing climate and human disturbance and pave the way for a sustainable groundwater management in the fractured groundwater systems from local to global scales.