In a state where nature produces multi-year droughts, and at a time when global warming is reducing the traditional Sierra snow pack, California must do more to understand and protect its precious water resource, according to a nationally known expert on the subject.
The expert is Roger Bales, a founding faculty member at the University of California at Merced and director of a multicampus UC research program aimed at promoting water security and sustainable usage.
Bales spoke last week at Livermore’s Bankhead Theater as part of the Rae Dorough Speaker Series.
The work done by Bales and his scientific colleagues, including a group at Lawrence Livermore National Laboratory, lies at the intersection of natural science and state water policy.
Water management is much more complex than simply having enough reservoir capacity to carry the state through dry years, Bales said.
It requires understanding the health of forests high in the Sierra Nevada, the watershed region where a century of fire suppression has left tree canopies so dense that a large fraction of precipitation gets sucked up with little left for runoff to urban or agricultural applications.
The same dense canopies screen the forest floor, making it more difficult for state water managers to use aerial surveillance methods to estimate snow pack for future melt runoff, he said.
Ironically, the dense canopies also increase the risk of devastating fires, he said. The close crowding makes forests drier and more vulnerable to complete destruction as California’s frequent multi-year droughts are exacerbated by rising temperatures worldwide.
Explaining the “basic arithmetic” of the water balance, Bales said that precipitation reaches a watershed as rain or snow, which then leaves either as direct runoff or as “evapotranspiration” – use by trees and other plants plus evaporation.
Runoff is the smallest of these three factors, he said.
When a devastating fire leaves a mountain region without vegetation, the next heavy rainstorm can produce torrents of destructive runoff, forcing water managers to deal with flooding instead of capturing the resource.
“We now know that (fire suppression) was a bad idea,” he said. “Fire is a natural part of the landscape. When you do fire suppression, there are more trees out there. In some of these places, there are six times as many trees because the big ones have been removed (by logging) and we’ve got lots of small ones.
He said, “When you double the biomass, to the first approximation, you double the water use in that same area.
"So that affects our water balance, what fraction of precipitation is coming off the mountain.”
In general, he said, thinner forests are healthier forests. He cited two basic ways to thin forests: mechanical cutting and burning.
Burning is nature’s way, but fires set by forest managers can bring obvious risks to health, safety and ultimately litigation. In addition, there are firm air quality restrictions on burning.
One key challenge for state water managers is to be able to make accurate estimates of the amount of water that will be available from future runoff.
These estimates must be made against a background of changing climate in which steadily rising winter temperatures mean that precipitation falls more as rain than as snow.
Snow pack has historically served as an upper elevation reservoir, releasing water steadily during the summer months. The trend toward smaller snow packs is already evident, he said.
For water resource managers, old-fashioned measurement techniques don’t always lead to reliable estimates of future water supplies.
Traditional rain and snow readings have been made from a few easy-to-reach mountain meadows and ridges, but these spot-checks do not necessarily reflect the reality of mountain precipitation at varying elevations over an area of hundreds of square miles.
On the other hand, the technology for snow and groundwater measurement has been improving, he said. For one example, he and his students are experimenting with radio-linked sensor networks that can sample and communicate precipitation at many more locations.
"You need more than five or 10 (locations), which is what’s out there now," he said. "You need more like 50, 60 – some places maybe 100 measurements.
"Then you can nail the amount of snow that’s out there."
Another development can be the use of aircraft based laser scanning systems, sometimes called LIDAR, which add to the information available.
In a year of low snowfall totals, he brought a laugh from the crowd when he said, “We will probably have operational systems that can measure snow accurately about the time we have more snow.”
Bales advocates public-private partnerships in dealing with California water issues, ranging from forest management to water storage.
Not surprisingly, given the importance of water to California’s multi-billion-dollar agricultural industry, he has found state officials receptive to the idea of further study to understand the vital headwaters region in detail.
In response to an audience question, he said forestry companies are anxious to help with forest restoration and have discussed the possibility of research partnerships.
“They’re afraid that their capital is going to burn if they don’t do this so they have both a self-interest and the public interest,” he said.
In answer to another audience question, he said he was not optimistic about getting further support from Congress, given resistance to spending in Washington.
A third audience question had to do with the possibility of expanding California water resources through the use of desalination.
Bales said he sees desalination as “one of the tools in the toolbox,” noting its widespread use in Israel, where there are relatively few alternatives.
A University of California colleague is testing a small desalination plant near Bakersfield “to try to show that the technology will work,” he said. In the meantime, California consumers have lower-cost options for purchasing water and the problem of waste disposal has to be solved before desalination becomes practical on a statewide scale.
Bales said that storage is critical for water security "in a dry climate like this.
"We have multiyear storage in the Colorado River basin; we have a little more than one year’s storage on our rivers in California.
"As we diminish the snow pack, that is a huge loss in storage. How do we make that up?
"Integrated management is something we've got to do."
