another planetary boundary overshot
Until 2022, freshwater use was one planetary boundary still within the safe operating space for humanity. The boundary was defined as consumption of no more than 4000 cubic kilometres of fresh water per year, with our actual consumption 2600 cubic km per year. No longer. A recent analysis by Johan Rockström, one of the originators of the planetary boundaries concept, and others, shows that we have broken the Earth's water cycle. Looking beyond freshwater consumption, they created two new freshwater boundaries: flow alteration of surface water, and extraction of groundwater. Surface water is critical to biodiversity, fisheries and drinking water. Groundwater contributes to river flows and sustains wetlands and plants. We are breaching both blue water boundaries.
The flow alteration boundary is flow regimes altered by more than 20 percent, which leads to significant impacts on freshwater systems and their ecosystem services. Globally we are within the boundary, but for a third of land areas home to half the human population, the boundary is exceeded.
For groundwater, the boundary is extraction not exceeding replenishment, and 47 percent of groundwater basins are in decline. We have extracted so much groundwater that the planet has shifted on its axis, moving the poles 80 centimetres, as water is redistributed from below to above ground.
In addition, there is a new green water boundary, the moisture in soil and atmosphere that amounts to two thirds of all freshwater. This powers the water cycle, including all biomass production. It secures food security, economic development and many livelihoods. Half of all rainfall comes from plant and tree transpiration releasing water vapour into the atmosphere. The boundary is the percentage of ice-free land in which soil moisture accessible to root systems deviates from its normal baseline for a whole month, as influenced by precipitation and evaporation. The limit is 10 percent and we are at 18 percent due to climate change and land use alteration such as deforestation. Tree loss in the Amazon has reduced rainfall in the region, and Congo basin deforestation has affected the rainy season in Nigeria and West Africa.
At the individual level, a single person household may average 150 litres per day in direct water usage, but 3000 litres a day including indirect water used to produce basic needs such as food, clothes, packaging, etc. That is 1200 cubic metres per person per year. A standard cup of coffee requires 140 litres of water to produce.
To fix the broken hydrological cycle, we need systemic changes, recognising water as a global common good rather than a national commodity to be fought over. There are no economics to do this at the moment. Deforestation must be controlled and climate change minimised. Farming uses about 75 percent of global water, often with subsidies for overproduction and overconsumption of water-intensive products in water-scarce regions. It would be better to grow water-demanding crops in wet countries and dry-tolerant crops in drier ones, and export them. Smart irrigation systems are another solution, as is recycling industrial waste water. Domestic water systems are full of leaks, and mixed sewage systems prevent treating rainwater and sewage separately, but rebuilding water infrastructure will take decades. More fundamentally, we need to secure the source of fresh water by managing the climate and nature.
SOURCE: based on Graham Lawton, "Wringing out the world", New Scientist 259(3453): 36-39. 26 August 2023
Last updated 15 September 2023