Focused groundwater recharge is controlled by landscape and climate

Focused groundwater recharge, the concentrated infiltration of water through surface features including streams, depressions, or fractures to the water table, is accepted as the dominant recharge mechanism in arid climates. As climates become increasingly arid, groundwater recharge is expected to shift towards focused mechanisms. Yet the magnitude of focused recharge, its spatial distribution and controls across climate zones remain poorly characterised at the continental scale. Here, we compare historical rainfall tritium with >1700 groundwater tritium measurements to assess the likelihood of focused recharge across the Australian continent, providing important context for water resources management, with global implications. 46% of bores assessed show evidence of focused recharge, suggesting that conventional recharge estimates based on diffuse mechanisms may substantially underestimate total recharge. We show that fractured rock and perennial watercourses are the main landscape features that strongly influence the likelihood of focused recharge. While focused recharge is most common in arid regions, it also occurs in wetter climates where fractured rock enhances subsurface connectivity. As aridity and climate variability intensify, understanding the landscape-climate interactions that enable focused recharge, and how shifts in energy and water availability alter the role of groundwater in the water cycle, will be critical to sustaining groundwater resources. Concentrated water infiltration was detected in 46% of Australian groundwater bores across arid and wet climates, suggesting that conventional diffuse-only recharge estimates may significantly underestimate total recharge, according to Tritium data from more than 1,700 samples.