A New Climate for Water Planners

Patrick McCully
Tuesday, March 25, 2008

The central assumption governing the design and operation of all major water projects has just been declared dead by a group of leading water and climate scientists. Designers and builders of dams need take note.

The scientists, led by Paul Milly of the US Geological Service, explained in a recent article in Science that our dams, floodwalls and sewers have been designed and operated under the assumption of "stationarity" - that natural systems fluctuate within a defined set of extremes that can be estimated from past experience. But climate change means "stationarity is dead" for water resources planning, the scientists say.

Two recent studies of the western US from scientists at the University of California's Scripps Institute show just how quickly streamflow is changing. One study found declining snowpacks and earlier spring river run-off over the past 50 years, all consistent with climatologists' models. The authors maintain that models for future warming mean "a coming crisis in water supply" over the next 20 years for an already water-stressed region."

A second study's findings were shocking even to longtime observers of US water resources. This study calculates that Lake Mead, the massive desert reservoir behind Hoover Dam, could run dry within 13 years if climate changes as predicted. There is only a 50% chance of there being enough water in the Colorado River within nine years to turn the turbines at Hoover. "We were stunned at the magnitude of the problem and how fast it was coming at us," the lead author told journalists. Lake Mead supplies almost all the water for Las Vegas and much of that used in southern California and Arizona.

The inability of water planners to cope with the new paradigm imposed by global warming is strikingly shown by a study on allocating Colorado River water in dry years, released last year by the Bureau of Reclamation. . . Although the issue under consideration was how to deal with hydrological extremes, the Bureau's study did not look at the impacts of climate change.

This head-in-the-sand approach unfortunately appears to be the rule in dam planning. While dam feasibility studies are now finally starting to mention the impacts of climate change, the norm seems to be that they do so only to dismiss them.

The recent economic study by Power Planning Associates Ltd. used to help justify the World Bank's approval of Bujagali Dam in Uganda dismisses the possibility of climate change altering flows of the Nile out of Lake Victoria (the source for Bujagali). "[C]limate change is not found to be significant enough in the medium term [to 2030] to influence hydrological scenarios" for this dam, say the consultants. Even more mind-boggling is the complete denial of the impacts of global warming in last year's environmental study for Ghana's Bui Dam by consultancy ERM. This claims that climate change will only affect dam safety and performance "over the very long term (i.e., thousands of years)."

To be fair to the consultants, there is as yet no agreed concept to replace stationarity. And it is never easy for professionals to discard the assumptions on which their training and careers have been based. Paul Milly and his colleagues suggest a framework for post-stationarity water resources planning, and it is clear that this must be based on broadening the range of potential flow scenarios and helping decision-makers understand the implications of increasing hydrological uncertainties.

But just pretending that climate is not changing, and encouraging governments to make major investments in climate-sensitive infrastructure on this basis is highly irresponsible. The government of the Caribbean nation of St. Vincent and the Grenadines noted in the UN General Assembly on February 13 that "[m]any of us are still paying for infrastructural investments that are no longer viable, or whose effective lifespan will be severely curtailed by climate change. Many of us have to borrow more to retrofit previous investments, which are often funded and designed and built by foreign lenders. It is illogical and immoral that we continue to pay developed creditor states for items whose very use is compromised by their actions."

If such calls for accountability become more common, water resource consultants may finally have to face a harsher climate reality.