Regional Hydrology
Increasing Soil Organic Carbon to Mitigate Greenhouse Gases and Increase Climate Resiliency for California
Figure 1. Calculated change in soil water holding capacity for the study area, and decrease in climatic water deficit for 1998 in inches of water per year following application of compost to increase soil water holding capacity.
Climate change poses severe risks to working landscapes in California, including rangelands and croplands, and the ecosystem services they provide. These services include food, habitat, carbon storage, and water supply for urban and rural communities, agriculture and wildlife. A healthy landscape can increase resilience to climate change, increase water quality and net primary productivity, and buffer the impacts of environmental stress leading to forest die-off, wildfire, flood and drought.
Rangelands and croplands, including publicly and privately managed lands, represent a majority of the land base in California. Increasing soil carbon can serve as a climate adaptation strategy due to its documented beneficial effects on soil erodibility, soil-water holding capacity, soil temperature and net primary productivity. Enhancing soil carbon in working lands at large spatial scales has the potential to measurably reduce greenhouse gas levels in the atmosphere, increase the sustainability of working landscapes and ensure the provision of other ecosystem services, including water, food and wildlife habitat. Application of composted urban and agricultural organic waste materials to grasslands and croplands, in conjunction with a suite of strategic land management practices, can remove significant quantities of carbon dioxide (CO2) from the atmosphere and sequester that carbon beneficially in soils and vegetation.
Numerous scientific studies have shown that increasing organic matter (OM) in soils can have multiple benefits, including carbon sequestration and reduction of atmospheric greenhouse gases (GHG)(DeLonge et al., 2014; Ryals and Silver, 2013, DeLonge et al., 2013). Soil management strategies and active management of working lands for enhanced carbon sequestration, such as "carbon farming," have a critical role to play in helping California develop resilience to climate change while simultaneously reducing atmospheric greenhouse gases. "Carbon farming" is a systems approach to land management that involves implementing practices that can improve the rate at which CO2 is removed from the atmosphere and converted to plant material and/or soil organic matter. Carbon farming integrates ecological site assessment and mapping in conservation planning, uses dynamic ecosystem carbon models to predict and measure increases in farm-system terrestrial carbon stocks, and incorporates hydrologic modeling to evaluate potential long-term impacts to on-farm water resources. Benefits of carbon farming include improvement in soil health, increased forage and crop yields, increase in soil-water holding capacity and reduction in total landscape demand for water, carbon sequestration, reduction of atmospheric greenhouse gases (GHG) and diversion of urban and agricultural organic waste from methane-producing anaerobic disposal in landfills and manure lagoons, and from burning.
Water that stays in the watershed can serve to preserve baseflows and riparian systems during low-flow periods and can potentially serve to sustain infiltration to the groundwater system. Figure 1 illustrates the calculation, using a hydrologic model, of a reduction in climatic water deficit (CWD) of 0 to 4.5 inches per year with a 25% increase in soil water-holding capacity (WHC) associated with increased soil OM for the northern Sacramento Valley. This reduction implies greater soil moisture, less irrigation demand, an increase in net primary productivity (NPP, equivalent to actual evapotranspiration), lower fire risk, and increased drought resiliency and carbon capture capacity.
The California Natural Resources Agency (CNRA), which is conducting the California 4th Climate Change Assessment (CCA) for non-energy-related projects, and is seeking new and innovative approaches to increase resilience to climate change, has funded this project. The Berkeley Energy and Climate Institute (BECI) is serving as the administrative office for agreements and reporting.
Objective and Scope
This project will use data generated from published and ongoing field and lab trials to constrain water-balance model estimates of soil moisture and evapotranspiration in order to quantify the potential changes in WHC and carbon sequestration for all rangeland and cropland soils statewide in response to increases in SOM. This approach will rely on current soil properties and calculate maximum potential benefit of increased SOM for all grasslands, pasture and arable lands in California. Limits to soil improvements will be illustrated, as not all of these lands would benefit from increases in SOM (e.g. wetlands, vernal pools, serpentine soils). Additionally, results will be used to estimate the economic value of both no-action and management actions leading to SOM increases, with respect to system hydrology and carbon sequestration for a representative sample of agricultural crops and rangeland types.
Finally, we will identify barriers to, and incentives for, statewide farmland and rangeland carbon storage enhancement within a climate-smart land-use planning framework under current and projected climate and land-use scenarios.
The development of state-of-the-art climate and hydrological surfaces for baseline conditions and future climates at a fine spatial scale will serve to inform other California 4th Climate Change Assessment projects. Significant integration with Project 2B submittal "Soil water dynamics, carbon sequestration, and greenhouse gas mitigation potential of using composted manure and food waste on California's rangelands" will provide leveraged opportunities for further understanding and model validation.
Relevance and Benefits
The proposed work directly addresses several aspects of the USGS Science Strategy for the Decade, 2007-2017 (U.S. Geological Survey, 2007), specifically "Understanding Ecosystems and Predicting Ecosystem Change, Climate Variability and Change." In addition to uncertainties about water supply, increases in landscape stress and wildfires are becoming more prevalent in California as a result of changing climate. Land and resource managers are seeking understanding as to the most scientifically defensible strategies for successful water-supply and resource management. This study will provide refined tools and information to manage and prioritize landscapes to increase resilience to climate change.Approach
This project is a collaboration with UC Berkeley, which is providing all data and field information for model calibration and modeling carbon sequestration under various management scenarios, USGS-Science and Decisions Center, which is estimating the economic benefits of management options, and USGS Western Geographic Science Center and the Carbon Cycle Institute, which are assessing barriers to rangeland and cropland preservation under socioeconomic and land-use scenarios.
Synthesis of available laboratory and field data and literature. We will use existing literature and ongoing investigations to identify data gaps; rangeland and cropland soils and landscapes with significant potential for enhanced carbon sequestration in response to strategic management; rangeland and cropland soils or landscapes with limited additional carbon sequestration potential; and Natural Resource Conservation Service (NRCS) and other conservation practices with significant statewide potential for SOM, GHG, water-holding capacity, and other climate adaptation benefits. Available data on soils, soil carbon, and other soil properties will be assembled and catalogued specifically to inform model parameterization for statewide sensitivity analyses. Expansion of current research efforts exploring the effects of compost additions to a drier grassland ecosystem, Sedgwick Reserve, a site that has had ecological research for decades and has rich data on soil characteristics, will support this task.
Calculate net carbon sequestration potential for California for rangeland ecosystems. To estimate the net potential carbon sequestration from compost applications to rangelands in California, we will parameterize a biogeochemical model, DayCent (Swan et al.), for the rangeland ecosystems, using empirical data from field research and climatic and other data from the literature. Once the model has been parameterized for each rangeland ecosystem of interest in the state, representing a range of bioclimatic and soil conditions, we will simulate one-time compost applications to these soils; the model will allow us to estimate changes in nutrient cycling (e.g., greenhouse-gas fluxes, net primary productivity, soil organic matter) due to the application. Comparing net fluxes with and without compost application will allow for estimation of net carbon sequestration resulting from compost additions.
For DayCent model validation, we will perform sensitivity analyses on the input data (e.g., climatic, soil, plant conditions), and compare results from trial runs to empirical field data from compost applications. For the sensitivity analyses, we will vary major model inputs to estimate the potential error in resulting estimates of trace-gas fluxes. To test the model against field results, we will use data collected real-time on Sedgwick Reserve. The sensitivity analyses and comparison to field data will allow us to understand the accuracy of model results, and iteratively improve the model's representation of compost application to California rangelands.
Using results from task 1, we will use a regional water-balance model (Basin Characterization Model, BCM: Flint et al., 2013) that has been developed for California for the historical period (1896-2015). The model will be parameterized with estimates of changes, resulting from management actions, in soil organic matter and associated soil properties using available data from task 1. Baseline conditions will be assumed using data from the USDA/NRCS SSURGO dataset (water content at field capacity and wilting point, porosity, depth, and percent organic matter) to calculate changes in hydrologic benefit in terms of recharge, runoff, actual evapotranspiration (net primary productivity), and climatic water deficit, and to calculate the capacity of each soil to benefit from maximum organic matter increase. Model results from task 1 will be used to constrain and calibrate the BCM where spatially coincident to provide validation and reduce uncertainty in statewide estimates. Estimates of spatially distributed carbon sequestration will be made on the basis of maximum potential change in soil organic matter statewide.
Future climate projections will be downscaled statewide for application to the BCM to establish maximum increase of SOM/SOC for future climates. Newly available future climate projections from the CMIP5 have been statistically downscaled to 6-km using LOcalized Constructed Analogs. There are 10 Global Climate Models available for representative concentration pathways (RCPs) 4.5 and 8.5, for a total of 20 future projections, providing daily precipitation and maximum and minimum air temperature. These projections will be aggregated to monthly and spatially downscaled to 270-m for application to the BCM (Flint and Flint, 2012). A selection of projections representing the estimated range in future temperature and precipitation conditions will be run through the BCM for baseline and enhanced soil conditions; simulation results will be analyzed to illustrate hydrologic resiliency to climate change with regard to available water supply, net primary production and environmental demand, and projected differences in carbon sequestration.
Given outcomes from Tasks 1 and 2, the on-farm/ranch, ecosystem service market and non-market benefits of managing rangelands and cropland for SOM increases will be estimated for a representative sample of agricultural land uses. The potential gross economic benefits and costs of increasing SOM through management actions (through on-farm/ranch soil-conservation and land-management practices summarized in Task 1) for selected crops and rangeland types will be estimated depending on available economic analysis. Where possible, we will estimate net benefits in terms of change in hydrologic components, runoff and recharge, and reduction in tons of GHG and the monetary value for a sample of crop and range production systems. From Task 2, the change in NPP from increased water holding capacity of soils can be used to estimate the economic value of increased production and/or avoided irrigation for selected high-value crops or supplemental feeding cost. Carbon sequestration values can be used to estimate private market value of sequestered carbon and/or the public social cost of carbon (SCC) from avoided GHG emissions over a 20-year period. In addition, a value map will be created showing the relative difference in gross economic benefits from enhanced SOM on a sample of California rangeland and farmland as compared with a "no action" business-as-usual (BAU) scenario.
We will analyze the current feasibility of selected agricultural practices designed and implemented for increased carbon storage to qualify for generating marketable carbon credits for either voluntary or regulatory carbon markets.
An assessment of how state policies and incentive programs can reduce barriers to implementing on-farm/ranch management actions at large spatial scales, including transaction costs associated with rangeland and cropland conservation, carbon sequestration, and climate adaptation, will be undertaken as part of this Task. We will also assess the potential for alternative public and private financial mechanisms, such as supply-chain investments, payment for ecosystems and climate services, local climate mitigation fees, revolving-loan funds, and others to remove barriers to adoption of soil conservation and land management practices that increase SOM. The assessment will quantify the gross benefits derived from policies, programs, and financial mechanisms that provide incentives for conservation and carbon sequestration enhancement for a representative sample of rangeland and farmland types.
An assessment of barriers to, and incentives for, rangeland and farmland conservation and management for increased carbon sequestration will be done, including identifying institutional challenges to integrating working lands into the cap-and-trade or other offset programs. Results in Tasks 1 and 2 will identify potentials for increased climate adaptation and mitigation through enhanced management on rangelands and croplands, for current climate and a selection of climate projections. We will identify current social, institutional and economic barriers to, and opportunities for, integrating rangelands and croplands into climate mitigation and adaptation programs. This will be accomplished through a review of the existing literature, stakeholder interviews, and expert opinion; options will be developed to overcome identified barriers and act on opportunities. Current best practices, model projects and programs, and innovative approaches to address these barriers will be identified and assessed for their applicability for deployment in California. We will apply a spatially-explicit scenario analysis of land-use change on rangeland and cropland, analyzing scenarios for both RCP 4.5 and 8.5 for no action + growth, management action + growth, and management + growth + future conservation (high, low).
The outputs from Tasks 2 and 3 will be intersected with growth scenarios to identify differences in economic and climate benefits of management activities with land-use patterns. Results will identify regions where high carbon-sequestration potential and high climate resilience overlap with regions of high development risk. The additional benefit of maintaining wildlife connectivity as an adaptation strategy will be explicit in the analyses by including data on linkage and habitat permeability priorities. By comparing scenarios we will identify the influence of land-use strategies on opportunities for land-management-based climate benefits.
Cooperating Agencies
California Natural Resources Agency
Berkeley Energy and Climate Institute (BECI)
References
DeLonge, M.S. et al. 2014, Greenhouse gas mitigation opportunities in California Agriculture, Nicholas Institute for Environ. Policy Solutions Report.
DeLonge, et al., 2013, A lifecycle model to evaluate carbon sequestration potential and greenhouse gas dynamics of managed grasslands, Ecosystems, 16(6), 962-979.
Flint, L.E., Flint, A.L., Thorne, J.H., and Boynton, R., 2013, Fine-scale hydrological modeling for climate change applications; using watershed calibrations to assess model performance for landscape projections. Ecological Processes 2:25.
Flint, L.E., and Flint, A.L., 2012, Simulation of climate change in San Francisco Bay Basins, California: Case studies in the Russian River Valley and Santa Cruz Mountains: U.S. Geological Survey Scientific Investigations Report 2012-5132, 55 p.
Ryals, R., and Silver, W.L., 2013, Effects of organic matter amendments on net primary productivity and green house gas emissions in annual grasslands, Ecol. Applications, 23(1), 46-59.
Swan, A. et al. COMET-Planner: Carbon and Greenhouse Gas Evaluation for NRCS Conservation Practice Planning, a project report to USDA/NRCS.
