Regionally divergent drivers behind transgressions of the freshwater change planetary boundary

Vili Virkki, Lauren Seaby Andersen, Sofie te Wierik, Dieter Gerten, Miina Porkka

Human-driven freshwater change contributes to elevated Earth system risks. Here, we advance the understanding of drivers behind the transgression of the planetary boundary for freshwater change (PB-FW), based on historical (1901–2019) streamflow (blue water) and soil moisture (green water) simulations from a large ensemble of global hydrological models. Since the former estimate ending in 2005, PB-FW transgression has increased across its blue and green water components. Decomposition of climate-related forcing and direct human forcing (encompassing land and water use changes) shows that climate has increasingly become the dominant global influence on dry and wet streamflow and soil moisture deviations from preindustrial-like conditions. Moreover, direct human forcings intensify particularly dry deviations in regions with compounding pressures on ecosystems. Our approach characterises the main drivers of blue and green water changes in regional hotspots, improving the utility of the PB-FW for guiding mitigation and adaptation strategies in response to freshwater change.