Remedies for streamflow depletion in the United States

By Isabel Jorgensen, WSPM student 2019-20

The average person uses about 4500 litres of water per day, 96.2% of which is “virtual” water contained in agricultural or industrial products. In the United States, 95% of the national water footprint is due to crop production, with just 7 crops accounting for 75% of groundwater consumption and 50% of surface water consumption. Speaking on 25 October 2019, Dr. Landon Marston, an American researcher from Kansas State University, tells us that this is causing substantial streamflow depletion in the nation’s rivers. He anticipates that streamflow depletion greater than 20% will have significant impacts on aquatic ecosystems.

To address this problem, Dr. Marston explains why we must understand who is driving this overexploitation of US rivers. The answer may seem fairly straightforward: agriculture is responsible for 95% of the nation’s water consumption, 74% of which occurs in just 10% of US counties. However, the problem is not so simple. Certain water-intensive crops are favoured by farmers because they are subsidized (5 billion USD is dedicated towards rice subsidies in Mississippi) or they are lucrative exports (11% of the UK’s blue water footprint comes from the USA, with rice constituting 26% of this). Thus, whilst the repercussions of agricultural water usage manifests in ways such as streamflow depletion, reducing this usage might be seen as economically inviable.

To this end, Dr. Marston proposes two remedies: rotational crop fallowing and improved water productivity. Using the Colorado River Basin as an example, Dr. Marston states that to prevent streamflow depletion exceeding the critical 20% threshold in the upper and lower basin, rotational crop fallowing would respectively need to save 345 MCM (million cubic meter) and 2391 MCM per annum. The room stirs with alarm at some of the figures, particularly in response to a statistic predicting a required reduction of 100% in cattle feed irrigation in the lower Basin to meet ecological needs.

Knowing he has captured his audience, Dr. Marston poses the question: “what if all water users adjusted their water use to match their industry benchmark level?”. His team’s forthcoming paper answers this question at length, but he gives us a preview. By using benchmarks to define scenarios of improved water productivity, they found that water savings would be greater in agriculture than in all other industries combined, and that alfalfa (a cattle feed crop) has the biggest potential to contribute towards this aim. Moreover, he notes that some basins have a greater potential to benefit from water savings (i.e. a different water elasticity) in regards to streamflow depletion. Recognising the serious implications for the cattle industry that his research has, and coming from a farming background himself, Dr. Marston drives home the point that the ultimate driver is our desire for cattle products. If we really want to see changes in agricultural water usage, we must align our consumer choices with these aims.

In short, agricultural water represents a major drain on US water resources, but also has huge potential for water savings through remedies like fallowing and increased productivity. Creating these water savings is critical to protect the ecological viability of the nation’s rivers and prevent significant ecosystem impacts that have consequences for other users. Moreover, and possibly most importantly, whilst fallowing and improving productivity show large potential water savings, these can only become actual water savings with proper policy and regulation. With two papers forthcoming (Richter al., in revision, Nature Sustainability and Marston et al., in preparation), Dr. Marston has certainly whet our palates for their findings.

 

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