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The review of more than 100 articles looked at 69 greater metropolitan areas that are acquiring 16 billion m3 of water through 103 reallocation projects to support 383 million people.

One proposed solution is recycling wastewater for reuse in irrigation

A new Oxford-led review published in Environmental Research Letters found that, particularly in the Global South, cities are draining their surrounding regions of water resources. This movement of water resources amplifies the effects of climate change, threatening to make dusty, depopulated wastelands of regions bordering cities. The review of more than 100 articles looked at 69 greater metropolitan areas — mainly in North America and Asia — that are acquiring 16 billion m3 of water through 103 reallocation projects to support 383 million people. That’s almost as much water as the annual flow of the Colorado River.

Tip of the Iceberg

Lead author Dustin Garrick, of Oxford’s Smith School of Enterprise and the Environment warned, “It’s a significant problem already and it is likely to grow,” and that we are, “woefully underprepared.” As troubling as the figures are, though, Garrick seems more concerned with data gaps. He said facts spotlighted by the review are “the tip of the iceberg due to blind spots in literature.”

These blind spots in the data, especially in the Global South, may obscure significant environmental justice issues. Water reallocations frequently have benefitted greater metropolitan areas to the detriment of the agriculture-dependent population in the countryside, leading to farmer protests when vital irrigation sources run dry.

Fair Water Allocation

Although the review does acknowledge that cities and surrounding agricultural areas are increasingly finding themselves in tight competition for water resources, it also points out positive movement toward more equitable water sharing.

The Mexican city of Monterrey is a good example of how cities can make their water relationships with surrounding areas less lopsided. In the 1990s, Monterrey diverted water from a Rio Grande tributary, but now compensates farmers and returns its wastewater for agricultural irrigation.

Likewise, plans for wastewater reuse and irrigation efficiency upgrades are being pursued within the often water-inefficient agricultural sector. These plans to leave more water for metropolitan areas often are happening due to a donor area’s positive response to water negotiations. The report affirmed that, “emerging trends related to irrigation efficiency and wastewater reuse can benefit from the progress and challenges encountered by early adopters.”

Water Reuse

New water reuse technology is making the process more available because of its energy efficiency and lower cost. One of the most promising examples is Fluence’s membrane aerated biofilm reactor (MABR), which recently proved itself in a yearlong pilot project at Stanford University, meeting California’s stiff Title 22 standards for irrigation reuse. MABR not only has shrunk the footprint of biological wastewater treatment, but it also has nearly eliminated the need for air compression, perennially the most energy-intensive process in biological wastewater treatment.

Although there is cause for optimism, the review cautions that polarization is a significant obstacle toward good decision-making. Often, reallocation of water from the countryside to a city is opposed out of hand as a net loss to rural areas, a belief the report calls a “myth.” However, the authors assert that policymakers also frequently rely on an alternate myth that irrigation efficiency will always deliver positive outcomes for both sides.

Cate Lamb, director of water security at the Carbon Disclosure Project, commented on the review’s conclusion that water reallocations can do better. “Water is a finite resource for which there are no alternatives,” she said. “It’s time to get serious about [it].”

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