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Mind the Gap

Go East, young man.  Image from USBR, 2012.

Last week, the Bureau of Reclamation released its Colorado River Basin Water Supply and Demand Study. According to the study the gap between available water from the Colorado and demand for water will continue to grow to over  3.2 million acre feet in the next fifty years (an acre-foot of water is the amount of water it takes to cover an acre up to a depth of 1 foot; it’s also approximately the amount of water used by a suburban household in a year). One of the goals of the study was to change how Reclamation considered future supply and demand. Traditionally the agency focused on only one projection of future demand. In this study though Reclamation considered multiple scenarios for supply and demand.

It is curious then that of the four supply scenarios in the study, only one considered the impacts of climate change. This however is not the first time that stakeholders have overlooked future variability in the Colorado.

When the Colorado River Compact was first negotiated, the parties used data from the previous several years in order to determine the “average” flow of Colorado that could be apportioned. Negotiators assumed that the future hydrology of the river would be similar to what they were experiencing in the moment. But that period (1905-1922) was abnormally wet, so much so that it had the “highest long-term annual flow volume in the 20th century.” This oversight has troubled the basin ever since, leading to water shortages and subsequent lengthy litigation.

Reclamation though may benefit from examining only one climate change scenario.  A strategy among climate deniers is to exaggerate uncertainty and point to disagreement among climate projections as evidence. By not considering other climate scenarios, Reclamation might stem debate on climate uncertainty with regards to the Colorado. What the agency risks however is again overestimating the amount of water that will be available in the Colorado Basin.

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