Posts Tagged: drought
How best to capture and store water for many different uses is a big question in California. After years of drought and now the looming possibility of a wet, El Niño-driven winter, safe-keeping any precipitation that does fall is a big priority for water managers. From reservoirs to tunnels to canals, the state's water infrastructure is vast and complicated. However, one approach with a lot of potential that has received little attention so far, at least in California, is managed aquifer recharge (also known as MAR) linked to collection of stormwater runoff.
Professor Andrew Fisher of UC Santa Cruz has been studying MAR for some time. He says it makes use of a variety of methods including infiltration ponds, wells, and in-channel modifications such as berms and inflatable dams to enhance groundwater supplies using water from many possible sources including hillslope and agricultural runoff and high flows in streams and wetlands. MAR has been widely used to augment water supply in Texas and Arizona, at many sites around the world, and in some parts of California. As an added bonus, MAR can help to improve water quality.
As an example, Fisher and colleagues have found that MAR can be used to both increase water supply and reduce nitrate contamination by enhancing denitrification. At one MAR site, the nitrate load reduction during infiltration was 50%, a rate of nitrate removal comparable to that achieved using traditional mitigation strategies like vegetative buffer strips. Interestingly, these studies also showed that the rate of denitrification increased with more rapid infiltration, up to a point. Fisher and his research group are exploring what controls denitrification rates during MAR, and whether MAR systems might help to improve the quality of stormwater runoff in a similar way. This potential to provide joint benefits for both water quantity and quality is something that many find attractive.
Another thing that Fisher notes is particularly valuable about MAR is that it can work in both drought and flood conditions, with a few caveats, of course. During high flow conditions, diversions can be used as a supply for MAR, helping to “take the edge off large events,” says Fisher, turning what was once considered a nuisance into a benefit. During drought, MAR can help to make the most out of short, flashy precipitation events. Fisher and colleagues have found that, even during a drought, “significant recharge benefit can be achieved if systems are designed to optimize runoff collection.” At the same time, droughts can be challenging for MAR projects that are based on runoff in terms of the consistency and quantity of water supply.
Whether in drought or flood conditions, proper design and placement of MAR infrastructure is critical. It follows that one of the biggest questions on the horizon for MAR researchers is where best to place the facilities, something Fisher and his students are working on now, generating regional maps and running models to evaluate where the most MAR benefit can be achieved.
Over the years, his research group has designed, built, and installed instrumentation at several MAR sites around the Central Coast of California. It can be hot, hard work, with upwards of 10 people in the field on any given day. His work is also dependent upon building and maintaining trusting relationships with landowners, agency staff, non-profits, and other stakeholder communities that his group works with as they develop and test projects under real-world conditions. Fisher says what while “each project is unique, we hope to find common elements that will assist in streamlining the design and implementation process.”
Given the uncertainty in California's water outlook, the state needs to adopt creative approaches for enhancing water supplies. Fisher's work suggests that managed aquifer recharge using stormwater runoff has a lot of potential. It will not be enough to resolve California's water shortages, but MAR can play an important role in a portfolio of sustainable water resource solutions.
This research was supported in part through a grant to Principal Investigator Andrew Fisher at the University of California, Santa Cruz from the California Institute for Water Resources in the University of California's Division of Agriculture and Natural Resources.
A recent paper from Pittenger and Hodel suggested that, at 9 percent, landscape water was not a large part of the overall California water picture. While I understand the desire to defend urban landscapes and justify the amount of water currently used to maintain them, I believe that view is short-sighted and would benefit from a broader perspective. For example, we should take into account both the history of drought in California and the profound changes caused by global warming that have begun and are predicted to accelerate as the century progresses.
The historic record of our region's climate over the past 2,000 years has been scientifically reconstructed from paleoclimate records. Researchers have studied the growth rings of long-lived trees and ancient stumps at the bottom of Mono Lake as a form of geological record that reveals previous water levels, as well as analyzed deposits deep under San Francisco Bay that collect sediment from a large watershed. The research and its implications are presented in “Climate Change and Paleoclimatology: 2013/2014 in Perspective” by Lynn Ingram, professor of Earth and Planetary Sciences at UC Berkeley.
Dr. Ingram suggests that we have experienced some of the warmest years on record since the turn of the century. She notes that the paleoclimate record shows that past periods of warming were associated with drier conditions in California. We currently have difficulty coping with droughts that last less than a decade, but during the medieval warm period there were two century-long droughts that had 60-70 percent of average precipitation. Indeed, our climate is influenced by cyclical patterns and Ingram states that “we see wet/dry cycles over the past 2,000 years with periods of 30, 65, 90, and 200 years.” She also states that “the past 150 years have been unusually wet when viewed over the past 2,000 year period. The 20th century was a wetter century and this is when all our water development population growth and agricultural industry were established.”
Ingram concludes “it's possible the climate may now be shifting to a drier regime. We have already seen the impact of warming that's been occurring since 1960. We are seeing a reduced snowpack that will continue into the future, and a drier climate with increased evaporation rates, so we'll have drier soils, more frequent wildfires, and increased dust levels.” It is also predicted that we will have a more extreme climate that will produce larger floods and deeper droughts in the future.
Considering the data and its implications, it's difficult to justify maintaining the status quo with respect to the use of water for landscape irrigation. Our water pie is not as large as we thought it was and it will need to serve more people in the future as our population continues to increase. We will pay more for water and have less to use, although this may be alleviated somewhat by desalination and reclaiming waste water. For example, the city of San Diego plans to raise water rates by 41% over the next five years. It also has a large desalination plant under construction and is considering claiming potable water from sewage water.
Potable water has been plentiful and cheap for several decades and as a consequence, we have not considered it a valuable resource. This attitude has begun to change during the drought, which is good because future conditions will require us to use water more efficiently and curtail wasteful practices. I believe it would be beneficial for the urban landscape sector to be proactive in this effort. We should lead by example and do what is needed to create sustainable water-wise landscapes that are less dependent on supplemental irrigation with potable water.
Using as much water as you desire and can afford and applying more potable water on a landscape than a site normally would receive from annual precipitation is not a sustainable practice. Realistic limits should be set on the amount of potable water used for landscape irrigation. We should encourage the creation of natural landscapes that require little supplemental irrigation. The current drought has provided an opportunity to reevaluate our landscapes, and the lessons we are learning on how to have functional landscapes with less water should not be forgotten, even if a rainy El Niño year temporarily refills reservoirs.
Drought is decreasing but not defeating the pathogen that causes sudden oak death, according to a citizen science-assisted survey conducted this spring by a UC Agriculture and Natural Resources forest pathologist. Results of the 2015 Sudden Oak Death...
This summer, the media frequently reported an increase in the density of pests in the home and landscape. The drought has been cited as the cause of these problems. Pest control companies quoted in articles confirm that the demand for their services is...
Do weed populations change during a drought? Does drought favor certain species? Does annual or perennial species matter? During this four year period of drought in California, have they changed? What are the populations of annual and perennial weeds?...