Demands from these uses would put at risk the supply of water to agriculture and ecosystems. Groundwater depletion could become the biggest threat to agriculture and urban water supplies in several regions. As a result, more than 40% of the global population - 2.3 billion more people than today - would be living in river basins under severe water stress. Water stress would be most severe in northern and southern Africa, and central and south Asia (Figure 2.9).