Precipitation partitioning into blue and green water resources is a fundamental hydroecological process shaping freshwater availability. This partitioning is determined by interactions among climatic conditions, land surface characteristics, and vegetation dynamics, which change with rising temperatures and CO₂ concentrations. Yet, global shifts in blue and green water shares and their management implications remain uncertain. We address this knowledge gap using climate simulations to quantify the relative partitioning of precipitation into green and blue water flows and its controlling factors. Here, we show that extreme five-day precipitation primarily drives partitioning shifts, favouring larger blue water shares. This effect is independent of baseline precipitation increases and generates larger blue water shares under both drying and wetting conditions. Additionally, interactions between leaf area index and plant water-use efficiency strongly impact regional partitioning trends. Our results translate shifts in blue-green water partitioning into an impact-relevant perspective, providing actionable context for water and land management.