Based on data from the 1970s and 1980s, Ryan Emanuel of North Carolina State University and colleagues found that some 40% of basins supplying transfers in the US are no wetter than their receiving basins. The result highlights the lack of attention to the sustainability of water supplies when managing inter-basin transfers, the scientists say.

"When we create inter-basin transfers, are we concerned about simply accessing more water, or do we care about the sustainability and resilience of those water supplies?" said Emanuel. "I would argue that more water doesn’t equate to a higher degree of sustainability and resilience, particularly if the transferred water is still vulnerable or sensitive to the same climatic factors that affect the receiving community. I think our results support this idea and hopefully serve as a call to synthesize existing inventory data and generate updated datasets on inter-basin transfers worldwide."

Inter-basin transfers typically take place through pipes, canals and aqueducts. One example is the 670 km-long aqueduct running from eastern California to Los Angeles, which in the early 20th century supplied the city with enough water to grow in area more than seven-fold. The transfer has always been controversial, with claims that it deprived eastern Californian farmers of a necessary resource.

Due to a lack of up-to-date records on inter-basin transfers, most studies have focused on individual transfer routes. But Emanuel and colleagues are concerned about the hydrological and climate effects of cumulative displacement. In the 1970s and 1980s, according to their calculations, inter-basin transfers in the US shifted 22 billion cubic metres of water every year – about 10 times more than the annual discharge of the river Thames in the UK.

To perform their study, Emanuel and colleagues digitized the historical data, and extracted each transfer’s size, start location and end location. Then, drawing on historical climate data and computer simulations of basins, they calculated the amount of rainfall and water runoff for each basin.

Supplying and receiving basins tended to share similar hydroclimatological conditions, the researchers found, suggesting that anything hydroclimatological driving a water shortage in a receiving basin was also driving a shortage in the supplying basin. Although some 60% of supply basins were wetter than the receiving basins, 40% were not.

"If planners and decision-makers intended [the transfers] to be resilient to climate variability and climate change … we might expect a stronger bias toward more streamflow in the supplying basins than [a] 60%/40% split, or we might expect a strong bias toward supplying basins with more precipitation or higher runoff ratios than we observed," said Emanuel. "We don’t observe these tendencies toward what could be considered resilience, leaving us to think that things like human demand for water, inter-basin transfer infrastructure cost and public policies play a larger role in determining how inter-basin transfers are structured than do considerations for the water balance."

The team published their work in Environmental Research Letters (ERL).

Related links

Related stories