SUBCALC

Criterion	Explanation
General Description	Land subsidence model used to simulate losses from aerobic microbial oxidation carbon losses, consolidation, wind erosion, burning and changes in soil organic matter content for Sacramento-San Joaquin Delta peatlands.
Model Domain	Sacramento-San Joaquin Delta
Developer	Hydrofocus, Inc.: Dr. Steven Deverel
Hardware computing requirements	The code doesn't have any specific computing requirement.
Code language	FORTRAN
Original application	SUBCALC, was developed to quantify and predict subsidence rates and causes on four Delta islands over the last few decades and to predict future land-surface elevation changes throughout the Delta to 2050. SUBCALC simulates subsidence due to aerobic microbial oxidation of organic carbon, compaction, wind erosion and burning. To estimate subsidence the model includes soil temperature control on organic matter oxidation rates, depth to groundwater and peat thickness. Availability of substrate for decomposition is adjusted annually, so soil losses rates decrease over the long term (Deverel and Leighton, 2010).
Public/proprietary and cost	Model and source code are proprietary of Hydrofocus, Inc. No associated cost for usage.
Physically or empirically based	The model is based on physically based processes but it is modified and calibrated using Delta specific measurements of subsidence and soil decomposition rates.
Mathematical methods used	Microbial oxidation: Michaelis–Menton enzyme kinetics, limited by soil organic carbon. Consolidation: Terzaghi's principle described using a linear relationship between compaction and hydraulic head changes and empirically derived from Delta specific studies. Wind erosion and Burning: Relationships based on empirically derived from Delta specific studies.
Input data requirements	Key input: soil parameters (organic matter content, soil organic carbon content, temperature, depth to organic soil), depth to groundwater. It is possible to prepare required inputs from publicly available climatic, and soil map information.
Outputs	Depth of soil lost annually (cm), also express as carbon flux (g C cm^-2 yr^-1). Out in the format of plain text.
Pre-processing and post-processing tools	Executable application file provided, along with input files.
Representation of uncertainty	No uncertainty integrated directly into model framework. Uncertainty can be assessed for each specific use. Model uncertainty was evaluated by systematically varying input parameters (soil organic matter fraction, soil bulk density, temperature dependent oxidation rate, soil temperature) based on input uncertainty, various combinations of input uncertainty were used to determine uncertainty in simulate subsidence (Deverel et al., 2016; Deverel et al., 2010b). Uncertainty was also evaluated by comparing simulated results to field measured subsidence (Deverel et al., 2010a). Estimates for subsidence are uncertain due to (1) spatially variable soil organic matter content, (2) spatial variability in factors affecting oxidative subsidence and consolidation (3) inability to fully quantify processes, and (4) empirical measurement error.
Prevalence	The model was mainly used for scientific publication specific to the Delta. Applications include estimation of land subsidence, accretion, CO₂ emission rates due to land usage (rice, corn, asparagus) and carbon capture in the Sacramento-San Joaquin island by various government, academic and private entities. The use of the model is allowed in the methodology for the carbon market "Restoration of California Deltaic and Coastal Wetlands", adopted by the American Carbon Registry in 2017.
Ease of use for public entities	Easy: model relatively simple to use once application file is obtained.
Ease of obtaining information and availability of technical support	No commercial help desk available. No internet user forums or user guide found. The model has mainly been used by Hydofocus personnel and is distributed on a personal base by Hydrofocus personnel, so doesn't require an active help desk. Descriptions of the model are available in Deverel et al. 2016, and Deverel et al. 2010a and 2010b.
Model and Source code availability	Source code available upon request to developers.
Status of model development	Model developed and available for use. The model is and will be periodically tested and updated when additional data of subsidence and/or ecosystem scale carbon fluxes for the Delta are and will be made available.
Challenges for integration	Fully quantifiable spatial resolution of soil organic carbon with great certainty is challenging with current data, this can limit integration with other models requiring high spatial resolution.

References

American Carbon Registry, 2017. Methodology for the quantification, monitoring, reporting and verification of greenhouse gas emissions reductions and removals from the restoration of California Deltaic and Costal Wetlands. Version 1.1. Available at https://americancarbonregistry.org/carbon-accounting/standards-methodologies/restoration-of-california-deltaic-and-coastal-wetlands/ca-wetland-methodology-v1.1-November-2017.pdf (accessed 26 October 2018).

Deverel, S.J., Ingrum, T. and Leighton, D., 2016. Present-day oxidative subsidence of organic soils and mitigation in the Sacramento-San Joaquin Delta, California, USA. Hydrogeology journal, 24(3), pp.569-586. http://doi.org/10.1007/s10040-016-1391-1

Deverel, S.J. and Leighton, D.A., 2010a. Historic, recent, and future subsidence, Sacramento-San Joaquin Delta, California, USA. San Francisco Estuary and Watershed Science, 8(2). doi:10.15447/sfews.2010v8iss2art1

Deverel, S.J. and Leighton, D.A., 2010b. Historic, recent, and future subsidence, Sacramento-San Joaquin Delta, California, USA – Appendix B: Subsidence Model. San Francisco Estuary and Watershed Science, 8(2).

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