In an article in Nature Sustainability published on the 16th of November, a team of researchers has assessed whether minimum human needs for water could be met around the world by using only surface water. This analysis forms part of a broader assessment of safe ‘earth system boundaries’ for freshwater. The planetary boundaries framework to which this research contributes uses earth system science and identifies nine processes that are critical for maintaining the stability of the earth’s basic environmental and life support functions. The research in this domain helps to identify whether humanity is acting sustainably for these nine key functions, one of which is freshwater.
In fact, scientists have already clarified the safe earth system boundaries for ‘blue water’, which consists of both our surface water and our groundwater. Remaining within safe planetary limits requires us to limit both the alteration of flow of surface water and the drawdown of groundwater. In rivers, flow alteration is one of the key drivers of biodiversity loss, and the rate of biodiversity loss in freshwater ecosystems is higher than any other ecosystem (83%). To meet environmental needs, we need to ensure that we alter no more than 20% of natural flows globally, leaving 80% unaltered to meet environmental needs. Currently we are operating within that limit, but 33% of the world’s land area is operating outside safe boundaries and therefore we have officially crossed the safe earth system boundary for surface water.
Groundwater, for its part, is essential to sustain plant life, supplying the root zone of plants with moisture, feeding local wetlands, and maintaining the flow of rivers. The safe operating space for groundwater is a situation in which the withdrawal of groundwater does not exceed the annual recharge rate. Across the world, 47% of basins are experiencing decline in groundwater levels, and therefore we are also operating outside the safe planetary boundaries for groundwater.
The article, however, went beyond the concept of safe planetary boundaries by examining our capacity to deliver a basic minimum quantity of water for all if we only used surface water. This is a key question for Sustainable Development Goal 6 on water and sanitation, in which the goal is to achieve universal access to safely managed water for all. Unfortunately, the researchers conclude that we are operating outside the system boundaries for minimum human needs (based, as mentioned above, exclusively on surface water).
The researchers found that 2.6 billion people live in river basins where groundwater is needed because they are already outside the safe limits of surface water diversion or have insufficient surface water to meet both the human needs and remain within safe limits. In addition, approximately 1.4 billion people live in river basins where demand management would be needed because they either already exceed the safe limits for surface water or face a decline in groundwater recharge and cannot meet minimum needs within the safe boundaries. Furthermore, 1.5 billion people live in river basins that are outside safe boundaries for surface water, with insufficient surface water to meet minimum needs, requiring changes both on the supply and on the demand side. As the researchers conclude, these results highlight the challenges and opportunities of meeting even basic human access needs to water and protecting aquatic ecosystems.