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.