Posts Tagged: climate change
Agriculture in California is on both sides of the climate change challenge. It is a sector that releases significant quantities of climate-warming greenhouse gases into the atmosphere. At the same time, it is vulnerable to the expected effects of climate change, including increased drought and flooding and more intense and longer heat waves.
Three review articles in the current issue of California Agriculture, the research journal of UC Agriculture and Natural Resources, summarize the state of knowledge on three topics at the intersection of climate and agriculture in California: agricultural resilience to climate change (“climate-smart” agriculture); cropland emissions of nitrous oxide, the most important non-livestock source of agricultural emissions; and opportunities for working lands to contribute to meeting state greenhouse gas targets.
The first article, Long-term agricultural experiments inform the development of climate-smart agricultural practices, discusses the research underway to incorporate resiliency in agriculture to extreme and unpredictable weather patterns induced by climate change.
The authors describe the “Century Experiment” at UC Davis. Established in 1992, the Century Experiment is a replicated research project that includes 72 one-acre plots planted to 10 different cropping systems. The plots will be monitored and data collected for a period of 100 years, but Californians won't have to wait that long to see results.
In the first 20 years, for example, testing has found that soil carbon increased significantly more in the organic tomato-corn system than it did in any other crops and management systems. Soil infiltration rates and aggregate stability were also greater in the organic than conventional tomato-corn system.
Soil amendments – such as agricultural and food wastes and winter cover crops – have led to increased soil carbon sequestration, higher infiltration rates and greater aggregate stability in the organic system, compared to conventional systems.
The authors believe maintaining healthy soils is a key to climate-smart agriculture. Properties such as porosity, water retention, drainage capacity, carbon sequestration, organic matter content and biodiversity all help to confer resilience to new pests, diseases and weather extremes brought on by climate change.
The second article, Nitrous oxide emissions from California farmlands: A review, presents the results of 16 California-based studies.
Nitrous oxide emissions are the largest direct source of greenhouse gases from cropland in California and nationally.
The studies reviewed in the paper indicate that the nitrous oxide emissions factor – the fraction of applied nitrogen that ends up being released as nitrous oxide – can vary widely depending on crop, irrigation method, climate and other variables. Accounting for these large differences is important in improving the accuracy of estimates of overall nitrous oxide emissions from farmland, and in designing measures to reduce those emissions.
The final article, Review of research to inform California's climate scoping plan: Agriculture and working lands, covers the range of ways that California's diverse agricultural systems can contribute to meeting the state's commitment to reduce greenhouse gas emissions by 40 percent from 1990 levels by 2030.
Slowing farmland conversion to urban uses and reducing emissions from the intensive livestock sector appear to provide the best opportunities for agriculture-related reductions. About two-thirds of direct agricultural emissions are from livestock production, particularly the dairy sector (the largest sector of the state's agricultural economy by annual revenue).
Because of the dairy sector's comparatively large contribution to agriculture's greenhouse gas emissions, the authors expect it to be a primary target for state climate regulations and incentives for emission reduction. They note, however, that policies should account for the already high levels of resource efficiency at California dairies.
The best opportunities for reductions in emissions from livestock operations center on feed and manure management. A report submitted to the California Air Resources Board says it may be feasible for California to achieve a 50 percent reduction in methane emissions from dairy if supportive practices are taken. Such practices might include:
- Switching from flush water lagoon systems to solid-scrape or dry manure management.
- Covering manure lagoons to capture biogas.
- Installing anaerobic digesters to capture and use methane.
- Use pasture-based dairy management.
The Legislature recently approved using $99 million in funds from the state cap and trade program to support the expansion of manure digesters and other technologies designed to greatly reduce emissions from livestock operations.
The review article also discusses potential for reducing greenhouse gas emissions from agricultural land in California by engaging in farmland and rangeland preservation, improved soil and nutrient management, integrating and diversifying farming systems, employing alternative practices in rangeland management and producing energy with biomass.
To help California forest property owners adapt to the changing climate, UC Agriculture and Natural Resources (UC ANR) has produced a 13-page peer-reviewed paper that outlines actions owners can take to sustain their forests' value even when temperatures rise.
“Managers of forest land have always had to adapt to changing conditions – such as markets, urban encroachment, droughts and floods,” said Susie Kocher, UC Cooperative Extension forestry and natural resources advisor. “We wrote this paper to help forest managers better understand the evolving science of climate change and how they can help their forests adapt to the climate of the future.”
Forests are shaped by the climates in which they grow. The current rapid pace of climate change has not happened for thousands of years, according to climate scientists. Nevertheless, the authors assure forest landowners that there are land management decisions they can make to ensure the resiliency of their resources, and perhaps even improve them.
“Some trees may grow faster under the warmer conditions we experience with climate change,” Kocher said, “especially those at highest elevation where there is adequate precipitation.”
The paper details the solid scientific evidence that indicates the rise in global average temperatures over the past 100 years. The temperatures, it says, “will likely continue to rise in the future, with impacts on natural and human systems.”
The document provides specific recommendations for care of three common types of forest in California: mixed conifer, oak woodland and coastal redwood forests.
Mixed conifer forests – typically composed of white fir, sugar pine, ponderosa pine, incense cedar and California black oak – are susceptible to moisture stress caused by warmer temperatures and reduced snow and rain. The drier conditions make the trees more vulnerable to fire and insect attack.
The drought of 2010-2016 has already had a substantial impact on mixed conifer forests in the Sierra Nevada. Aerial detection surveys show that more than 102 million trees have died since 2010; more than 62 million died in 2016 alone.
The UC ANR climate change adaptation paper suggests reducing competition for water by thinning trees and managing for species and structural diversity. The authors suggest property owners consider the source of seedlings when planting new trees.
“Select seedlings adapted to a slightly lower elevation or latitude than your property,” Kocher said. “These would be more likely to thrive under the 3- to 5-degree warmer temperatures we expect in 50 years or so.”
Oak woodlands are widely distributed and diverse in California, which gives them moderate to high capacity to adapt to climate change. Mature oaks are more resilient than young trees and seedlings.
One potential impact of climate change on oak woodlands is increasing precipitation variability and increasing spring rains. The moisture change could increase the spread and prevalence of Sudden Oak Death (SOD), a disease caused by a bacterium that was introduced into California from outside the U.S. SOD is primarily a concern in areas with tanoaks in Central to Northern California coastal areas.
“To reduce the spread of sudden oak death, land owners should prevent the movement of infected leaves, wood and soil,” according to the paper.
The primary concern for coastal redwood forests is the decline in fog. Fog frequency in coastal redwoods is 33 percent lower now compared to the early 20th Century. Less fog and rain plus warmer temperatures would leave coastal areas where redwoods typically thrive drier. But that doesn't mean redwoods will disappear. Areas with deep soil and areas close to streams and rivers may provide refuge for redwood forests.
The new publication, Adapting Forests to Climate Change, can be downloaded free from the UC ANR Catalog. It is the 25th in the Forest Stewardship series, developed to help forest landowners in California learn how to manage their land. It was written by Adrienne Marshall, a doctoral student at the University of Idaho; Susie Kocher, UC Cooperative Extension forestry and natural resources advisor; Amber Kerr, postdoctoral scholar with the UC John Muir Institute of the Environment; and Peter Stine, U.S. Forest Service.
Of 12 crops examined in Yolo County, walnuts are most vulnerable, while processing tomatoes and alfalfa acreage may increase due to warmer winters.
In an effort to forecast how climate change may affect agriculture, University of California agricultural economists looked at how climate has affected crop acreage in the past. The effect of temperature changes on plants depends on local conditions and the crops grown. In a case study of Yolo County agriculture, warmer winter temperatures would reduce chill hours, potentially reducing yields for some crops while extending the growing season for others, according to a University of California study published in the peer-reviewed journal California Agriculture.
This technique used in Yolo County could be used for projecting the effects of climate change on agriculture in other regions, said Lee.
Using about 100 years of climate data and 60 years of farm acreage, Lee and her co-author looked at the relationships between the evolution of local climate conditions and the acreage of 12 major crops grown in Yolo County. The crops included processing tomatoes, rice, alfalfa, wheat, corn, prunes, grapes, walnuts, almonds, safflower, pasture and other fruit.
“When we look at maximum and minimum temperatures, the minimum temperatures are higher while the maximum temperature stays about the same,” Lee said. “And the lower temperature is rising at a faster rate, especially in winter. That's good for winter crops, but not so good for crops that require chill hours.” Many tree crops require cold for a certain number of hours below a critical temperature, commonly 45 degrees Fahrenheit, to stimulate the growth of leaves and flowers.
Among trees and vines, the most sensitive to climate change are walnuts, which require more chill hours. Walnut acreage would decline, Lee said, while there would be a modest change in grape and almond acreage.
Lee emphasized that market conditions exert a great deal of influence on the crops growers choose to plant. Growers who consider trends in climate change may choose different cultivars rather than different crops, such as a walnut variety that requires fewer chilling hours.
Lee and co-author Daniel Sumner, director of the UC Agricultural Issues Center and Frank H. Buck, Jr. Professor in the Department of Agricultural and Resource Economics at UC Davis, based their acreage projections on following the trend of climate change for the past 105 years, but were not able to incorporate climate variability, extreme weather events, accelerated warming or availability of irrigation water in their modeling.
This research, which was part of a larger study of climate change and agriculture funded by a grant from the California Energy Commission, was also supported by the UC Agricultural Issues Center, a program of UC Agriculture and Natural Resources.
“We have long known that stream revegetation improves wildlife habitat and enhances water quality, but that fact that the vegetation and trapped sediment capture carbon underscores the importance of this conservation practice,” said David Lewis, a UC Agriculture and Natural Resources (UC ANR) watershed management advisor for Marin, Sonoma and Napa counties.
Going back to the time when Gen. Mariano Guadalupe Vallejo was running long-horn cattle on a vast tract of land in Alta California, ranchers didn't always understand the value of the trees, shrubs and grasses that grew around rangeland waterways.
Vallejo removed vegetation because it provided a hideout for grizzly bears that attacked his cattle and pilfered hides being tanned. In later years, authorities coached landowners to alter streams and remove plants to increase stream flow and improve flood control.
Beginning in the 1960s, the environmental impacts of removing trees and plants became apparent and public funds were made available to share in the cost of restoring streamside vegetation on private land, said Lewis, who is also director of UC ANR Cooperative Extension in Marin and Napa counties. Over a period of three years, he and a team of UC and local scientists studied the stream revegetation projects that took place from about 1970 to just recently. They documented the carbon sequestration benefits of stream revegetation and calculated the value based on the current market for carbon credits. The results were shared in a report released this month, Mitigating Greenhouse Gas Emissions through Riparian Revegetation.
“In Marin County, for example, the cost per metric ton for carbon dioxide equivalence sequestered with revegetation was $19.75. The carbon market is currently paying about $12.50,” Lewis said. “There is about $7 that we haven't made up. But when you think about the other benefits of riparian restoration – reduced sediment, restored habitat for migratory songbirds and other wildlife – I would bet that value to be much greater than $7.”
Lewis' research will be of interest to county governments as they strive to reduce total greenhouse gas emissions to comply with the requirements of the 2006 California Global Warming Solutions Act (AB 32). The legislation requires California to reduce its greenhouse emissions to 1990 levels by 2020. As part of the law, local governments must write a “Climate Action Plan” to report how they will monitor and track progress in reducing and offsetting greenhouse gas emissions.
“It may make sense for governments and project proponents to invest in creek restoration and other farm conservation practices to reach and surpass their carbon emission reduction goals,” Lewis said.
Through 1990, Marin ranchers restored more than 25 miles of stream with willows, oaks and other trees and shrubs. Those plants trapped sediment contain an estimated 80,265 metric tons of sequestered carbon – an amount equal to emissions from 61,959 passenger cars in one year.
Lewis estimates there are several hundred miles of unrestored streams in Northern California coastal counties. And the implications of this study have application for rangeland streams throughout California.
“This represents tremendous potential for carbon sequestration,” Lewis said. “And rancher interest in stream restoration has never been higher. Working with the ranchers to plant trees and shrubs along our waterways presents a significant opportunity to offset carbon emissions.”
An initiative to maintain and enhance sustainable natural ecosystems is part of UC Agriculture and Natural Resources Strategic Vision 2025.
“Even recent large storms, while welcome, have not made much of a dent in the state's water deficit after several hot, dry years. This drought, ongoing for three years and counting, presents several complex, important issues,” writes Faith Kearns, Ph.D., a water analyst for the UC Agriculture and Natural Resources' California Institute for Water Resources.
So what makes dealing with drought in California so complex?
Kearns has written “5 Key Facts about the California Drought—and 5 Ways We're Responding to It” to provide some answers to that question.
- California's depends on water from the winter snowpack to get through California's dry summers.
- Lynn Ingram, professor in the Department of Earth and Planetary Science at the University of California, Berkeley found that the state has previously experienced periods of prolonged drought and may be entering another dry period.
- Global climate change seems to be exacerbating the drought.
- Pumping groundwater to compensate for the shortage of surface water for agriculture has softened the economic impact of the drought, but is having detrimental effects on residents whose wells have dried up. Groundwater depletion is also causing land to sink.
- People and animals are suffering. “Some areas of the state where people have been the hardest hit are also the poorest, creating cumulative stressors and threatening livelihoods,” writes Kearns. “Furthermore, wildlife and ecosystems have been severely impacted by the drought.”
She also writes about five ways California is dealing with the drought: through legislation, spending on water projects such as water storage, reducing reliance on water transfers from other regions, managing water more efficiently and raising community awareness.
“The state's universities have been holding workshops and offering training opportunities for communities hit hard by drought, agriculture and ranching,” Kearns writes. “People are starting to realize the scale of change necessary and are joining together in non-traditional alliances.”
You can read Kearns' complete drought article on Hippo Reads.
The Public Policy Institute of California is holding a conference on managing drought on January 12 in Sacramento. The event, supported by the California Water Foundation, will bring together university researchers, legislators, farmers, environmentalists, regulators and other stakeholders together to discuss the drought, water management and policy. To register for the event webcast, visit http://www.ppic.org/main/event.asp?i=1623. You can follow the conference on Twitter with the hashtag #ppicwater.