Spatiotemporal dynamics of global rain-fed groundwater recharge from 2001 to 2020

Abstract

• Global rain-fed groundwater recharge averaged 176 mm a −1 from 2001 to 2020. • Rain-fed groundwater recharge declined in 40% of river basins during 2001–2020. • 22% of global basins are hotspots where drying recharge worsens storage loss. Groundwater depletion results from a groundwater withdrawal rate exceeding groundwater recharge. Although groundwater depletion is recognized as a pressing global phenomenon, global groundwater recharge remains one of the least constrained aspects of the global hydrological cycle. This study aims to evaluate the spatial and temporal variations of global rain-fed groundwater recharge over the last two decades (2001–2020), and to assess how climate change and variability have affected the temporal patterns of groundwater recharge. We developed a three-layer transient water balance model to estimate the daily dynamics of global rain-fed groundwater recharge at a spatial resolution of 0.1°. The 20-year average groundwater recharge is estimated to be 176 mm per year. The assessment of the global recharge trend shows that the global groundwater recharge trend has increased by 0.2 mm per year during these 20 years. However, when evaluating the recharge trend of each global river basin, we found that recharge has declined in 40 % of the river basins. These declines are primarily located in South America and Europe, with additional scattered basins in northern Australia and eastern China. In 26 % of the world’s basins, declining groundwater storage combined with increasing groundwater recharge, suggests that storage loss is likely due to anthropogenic factors such as over-exploitation, affecting 2.69 billion people. In contrast, in 22 % of basins, the decline in groundwater storage coincides with a decline in groundwater recharge. These basins, inhabited by 1.69 billion people, are climatic hotspots for groundwater sustainability, where drying recharge exacerbates groundwater storage losses.

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