Safe and just Earth System Boundaries for blue water

Surface and groundwater are critical to the health and livelihood of ecosystems and communities everywhere. But do we have enough blue water, on a global scale, to support healthy people and environments given the way we currently use our water resources?

Published in Nature Sustainability, a recent Griffith University study explores whether human needs can be met within river basins with the surface water and groundwater available without operating beyond safe and just Earth System Boundaries (ESBs).

Australian Rivers Institute Senior Research Fellow Dr Ben Stewart-Koster said the analysis follows on from earlier research output defining ‘safe and just’ ESBs, and steps towards providing parameters for safe and just ESBs for blue water.

“ESBs are about planet-level stability of the biosphere, the hydrosphere and the atmosphere. Safe and just ESBs quantify the conditions that are needed for the planet, but also everything that lives on it, to thrive,” he said.

“Quantifying safety and justice is a big part of the work needed to provide an integrated set of parameters to protect the world’s resources and create conditions that are necessary to sustain ecosystems, communities and economies.

“Our aim is to provide guidelines, or guardrails, within which planetary stability can be assured or protected. The justice side of the coin is to provide a set of guidelines that protect people from significant harm from earth system change. In the context of blue water, it's about protecting people from harm caused by changes to surface and groundwater flows.”

Stewart-Koster said assessing safe and just ESBs for blue water is particularly important due to the ecosystem services the resource provides, as well as its fundamental connection to food security.

“Blue water is a really critical component of the earth system, including its connection with biodiversity. From a planetary point of view, blue water provides many services. There is drinking water, an obvious one,” he said.

“But we also know that 75% of the world's coastal fisheries’ catch comes from species that rely on freshwater flows at some stage of their life cycle. Disruptions to blue water flows can negatively impact food security in many parts of the world.”

“Flow alterations are, to an extent, robbing Peter to pay Paul. We know that changes to flow, particularly in Australia, will lead to a reduction of fisheries productivity and loss of carbon storage in wetlands. We know we divert water for one use at the expense of another.

“We may choose that and each society makes that decision of what is acceptable. The research is about making sure we can make a conscious decision about water choices and what the impacts will be.”

Drawing boundaries

The study involved a review and analysis of global flow-ecology literature with the aim of quantifying what safe and just levels of blue water use actually look like, Stewart-Koster said, and the results showcase that the ESBs for blue water are quite strict.

“We defined surface water ESBs at basin scales, and groundwater ESBs at aquifer scales. The surface water ESB is that we limit flow alteration to 20% of monthly river flow, leaving 80% for the environment,” he said.

“That is quite a limited amount of water that we can alter to stay within that boundary. The safe and just ESB for groundwater is that natural and anthropogenic drawdown (pumping and natural discharge) should be no greater than the average annual natural recharge.

“So, in years where there’s limited groundwater recharge, it becomes all the more important to create conditions that protect groundwater-dependent vegetation and wetlands.

“In terms of what the science says about preventing significant harm to ecosystems and people from earth system change, limiting flow alteration to 20% will help to achieve that goal. We may be able to alter flows beyond that level but, where local information is absent, we recommend that 20% is a safe and just starting point.”

Based on these guidelines, Stewart-Koster said that, in many places around the world, safe and just ESBs for blue water are already dramatically exceeded.

“Our study found that 2.6 billion people, almost a third of the world’s population, live in river basins where groundwater is needed because they are already exceeding the surface water Earth System Boundary or have insufficient surface water to meet human needs,” he said.

“Analysis shows that approximately 1.4 billion people live in river basins where a transformation of water demands is needed as they either exceed the surface water Earth System Boundaries or currently face declining groundwater recharge and cannot meet minimum needs.

“We see a further 1.5 billion people live in river basins outside the Earth System Boundaries, with insufficient surface water to meet minimum needs, requiring transformation in both water supply and demand.”

A global effort

Stewart-Koster said the overriding message from the research results is that there is a huge amount of transformation required on a global scale to meet the safe and just ESBs and protect people alongside the planet.

“Of the world’s population, we found that there are about 2 billion people who live in river basins where they can provide minimum water needs for all people inside the ESBs, essentially protecting aquatic ecosystems and the ecosystem services they provide,” he said.

“Given that there are billions of people who live in places where there isn't enough water to provide for basic human needs, what transformation do we need to make in the way we produce food and the way we secure water?

“The transformations that society needs to make are going to be different everywhere. It will always depend on the local context. But the data shows that in some parts of the world we really need to change the supply side.

“And then there are places where the demand needs to change, where we don’t have a lot of surface water and where groundwater systems are in trouble, as well. It is very much a value judgment that each society has to make for itself.

“The narrative that emerges is about just how far beyond the ESBs we actually are. The biggest difficulty this work has revealed to us is the challenge of transforming the way we use all of our resources, but particularly our blue water.”

Given how big the discrepancy is between availability of blue water and demand in many places, there’s going to need to be a global effort, Stewart-Koster said.

“There really needs to be a world- and economy-wide embrace of these concepts if we are going to achieve this transformation,” he said.