Caves demonstrate decrease in rainfall recharge of southwest Australian groundwater is unprecedented for the last 800 years

Billions of people worldwide rely on groundwater. As rainfall in many regions in the future is projected to decrease, it is critical to understand the impacts of climate change on groundwater recharge. The groundwater recharge response to a sustained decrease in rainfall across southwest Australia that began in the late 1960s was examined in seven modern speleothems and drip waters from four caves. These show a pronounced increase or uptick in regional drip water and speleothem oxygen isotopic composition (delta O-18) that is not driven by a change in rainfall delta O-18 values, but is in response to the shallow karst aquifers becoming disconnected from rainfall recharge due to regional drying. Our findings imply that rainfall recharge to groundwater may no longer be reliably occurring in this region, which is highly dependent on groundwater resources. Examination of the longer speleothem record shows that this situation is unprecedented over the last 800 years. Regional drying in southwest Australia over the past six decades has resulted in a decrease in rainfallassociated recharge of aquifers which is unprecedented over the last 800 years, according to speleothem oxygen isotope data from four cave systems.

Automated summary

Billions of people worldwide rely on groundwater, but the impacts of climate change on groundwater recharge are not well understood. A study in southwest Australia found that a sustained decrease in rainfall has led to a disconnect between shallow karst aquifers and rainfall recharge, implying that groundwater recharge may no longer be reliable in this region. This situation is unprecedented in the last 800 years.