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Wet Water Shortage (video)
November 08, 2001

Interviewee: Peter Gleick, Pacific Institute.

Video is 1 min 42 sec long. Please be patient while it loads enough to start playing. Requires the free QuickTime plug-in.


If you prefer to view the movie with RealPlayer, click here.

Produced by Brad Kloza

Copyright © Center for Science and the Media, with additional footage from UCAR, EPA, Pacific Institute, Act Now Productions, American Water Resources Association and NBC.

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How could a prediction of more rain lead to worries about less water?

As this ScienCentral News video reports, it’s something else we can blame on global warming.


More from Peter Gleick

Peter Gleick, director of the Pacific Institute for Studies in Development, Environment, and Security, was the lead author of the Water Sector Report for the government-mandated National Assessment of the Potential Consequences of Climate Variability and Change for the Nation. Following is more of his interview with stn2:

The National Assessment was a comprehensive multiyear effort by many different people to look at the impacts of climate change on the U.S. The goal was to bring together scientists and members of the public, representatives of the water community, academics, businesses—to review what we know and what we don’t know about the science of the impacts of climate change and water in the US. As a whole the National Assessment was without a doubt the most comprehensive study of the implications of climate change for the U.S. ever done.

The report concluded that with a high degree of confidence that global climate is going to change. There’s a very strong consensus in the scientific community now that climate change is a real problem—that it’s coming, that in fact there’s nothing we can do to prevent some climate change from occurring. But in addition the assessment concluded, as has much of the scientific community, that we’re already seeing evidence of global warming, that global warming is already having an impact on the water resources of the United States. We’re already seeing changes in the timing of runoff, we’re seeing changes in temperature and increases in sea level, we’re seeing changes in storm patterns in the U.S. The reality is climate change is a real thing, and we’re not prepared to deal with it.

In addition, as confident as we are that global climate change is going to occur, we’re confident, unfortunately, that the impacts of climate change are going to increase in the future. That as we make more greenhouse gases, we’re going to see more and more climate change. Even if we were to try to implement policies to reduce the emissions of greenhouse gases today, those policies would not be able to slow the rate of climate change for quite some time. We’re committed to some climate change in the future no matter what we do.

As the earth warms up, that’s going to cause a whole series of changes to things that we care about in the water area: changes in precipitation patterns, changes in how much water evaporates from the surface of the earth, the way snow falls and the way snow melts. And one of the most important impacts that the National Assessment identified was the effects that rising temperatures will have on snow. In particular, thew way that rising temperatures will change what would have been snow perhaps into rain.


In the western US, much of the precipitation that we get actually comes in a very short period of time. In California for example, we get almost no rain at all between may and October. And all of our precipitation comes from October through the winter months to spring, ending perhaps in April. In the mountains in the west, most of that precipitation falls as snow, and it’s stored in the mountains as snowpack. When it melts up in the spring, it begins to run off, and that runoff feeds our rivers and lakes and streams throughout the drier parts of the year. Our water managers are dependent on that snowpack.

As global climate change gets worse and worse, we’re going to see more of this precipitation fall as rain. That will run off right away. That means winter runoff is going to grow. We’re going to get more runoff in the winter periods, which is precisely the time we don’t want it. We don’t want a lot of winter runoff, because that’s when we get the worst flooding and the worst damages from floods. At the same time what that means is that less of the snowpack is going to be available to run off in the spring and the summer. And so runoff in the spring and the summer is going to decrease. We’re going to get less runoff at the time of the year when we need it the most. This is the worst of both possible worlds.

Another important conclusion is that scientists are increasingly concerned about the implications of global climate change in all of its dimensions for the natural environment. Plant and animal communities have developed with the past climate as a guide. They’ve moved into regions where the climate has been favorable to them. And as global warming occurs, as climate change begins to make itself apparent, the implications for our natural ecology are likely to be quite traumatic, in particular for aquatic ecosystems. Aquatic ecosystems depend on receiving certain amounts of water at certain times of year. They depend on certain water temperatures at certain times of year for spawning or for reproducing. They depend on certain kinds of plant life for survival. And ecologists are increasingly concerned that global warming will cause very dramatic impacts on fish and wetland habitat. And in much of the US we’ve already damaged much of our aquatic ecosystem. We’ve filled wetlands, we’ve destroyed marshes, and global climate change is going to make many of those problems worse.

The entire water supply system of the US—our dams, our reservoirs, our aqueducts—are designed and built on the assumption that tomorrow’s climate is going to look like the past climate. And one of the conclusions of the National Assessment report is that that’s no longer a good conclusion. We can no longer assume that the future is going to look like the past. In fact, we now believe that the future is going to look quite different than the past in terms of climate. Our precipitation patterns, our temperatures, our storm patterns—are going to be different. That’s a problem for our water systems. We’re not prepared to deal at the moment with the changes in climate that we now expect are coming. It’s time for water managers, the people who control the reservoirs, who run the hydroelectric facilities, to start to think about climate change as a real part of their future.

From the National Assessment

Following are some of the findings in the National Assessment Water Sector Report:

"The greatest increases in temperature are expected to be in higher latitude regions."

"Higher temperatures will have several effects: They will increase the ratio of rain to snow, delay the onset of the snow season, accelerate the rate of spring snowmelt, and shorten the overall snowfall season, leading to more rapid and earlier seasonal runoff."

"As early as the mid-1980s, regional hydrologic studies of global warming impacts suggested with increasing confidence that higher temperatures will affect the timing and magnitude of runoff in these regions … Over the past two decades, this has been one of the most persistent and well-established findings on the impacts of climate change for water resources in the US and elsewhere."

Using two different models, the report found that "as a result of the higher temperatures, both models show large decreases in April 1 snowpack for all of the snow sites in the western US, with the exception of the Central Ricky Mountain region," which showed decreases in only one of the models. "In some of the more extreme cases, model snowpack is completely eliminated by the end of the next century."

"Recent field surveys corroborate the findings" that higher temperatures will lead to a decrease in the extent of snow cover in the Northern Hemisphere. "Snow cover over the Northern Hemisphere land surface has been consistently below the 21-year average (1974-1994) since 1988, with an annual mean decrease in snow cover of about 10 percent over North America."

"Other effects include earlier lake ice melting, earlier snowmelt-related floods in western Canada and the western US, and earlier warming of Northern Hemisphere land areas in the spring."

One study "found a statistically significant trend toward earlier spring runoff in west-central Canada on more than 70 percent of 80 natural rivers, primarily since 1950."

Another study, "reported that between 1948 and 1991, snowmelt-generated runoff came increasingly early in the water year in many basins in northern and central California. A declining fraction of the annual runoff was occuring during the months of April to June in middle elevation basins, and that an increasing fraction was occuring earlier in the water year, particularly in March."

Another study observed the same basic pattern in an analysis of the Sacramento and San Joaquin Rivers over the entire 20th century." This was shown to be the case "even correcting for human water withdrawals and the operation of reservoirs." The work "was confirmed by an analysis showing the relationship between decreased spring snow cover and streamflow in the northwestern U.S. and Missouri River Basin."



by Brad Kloza


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