Downscaling Map Atlas

Statewide Carbon and GHG Projections Under Agricultural Management Scenarios

Author

Akash B V

Published

April 10, 2026

Summary of Key Findings

This atlas presents statewide projections of soil carbon storage and greenhouse gas emissions under six agricultural management scenarios for California’s annual croplands (~132,000 fields across 57 counties). Results are produced by the SIPNET ecosystem model at representative anchor sites and downscaled via Random Forest to all cropland fields.

Validation Status

These results are from a proof-of-concept modeling framework that has not been validated against field observations. Interpret all values as illustrative projections, not empirical estimates.

Scenario Comparison

Percent change from baseline across all California annual croplands (ensemble mean, n = 20). a CH4 fluxes are effectively zero for non-flooded annual crops. Methanogenesis requires continuous flooding (e.g., rice paddies), which is not included in this analysis. Percentage changes from a near-zero baseline are misleading and are omitted.
Scenario Soil Carbon N2O Emissions CH4 Emissionsa
Compost +12.2% -39.5% n/a
Reduced Till +0.2% +0.1% n/a
Zero Till +0.4% +0.5% n/a
Drip Irrigation +3.3% +12.0% n/a
Stacked (all) +16.6% -27.3% n/a

Statewide Absolute Magnitudes

Statewide totals across 1.86 million hectares of annual cropland (57 counties, ~132,000 fields). SOC is end-of-simulation stock (2024) at 30 cm depth. N2O and CH4 are annual emission rates in gas mass units. Values are ensemble means (n = 20).
Variable Baseline Compost Reduced Till Zero Till Drip Irrigation Stacked
SOC (Tg C) 112.3 125.9 112.5 112.7 115.9 130.9
N2O (Gg N2O yr⁻¹) 12.91 7.81 12.92 12.98 14.46 9.39
CH4 (Gg CH4 yr⁻¹) 0.014 0.015 0.013 0.013 0.014 0.017

CO2-Equivalent Summary

Net CO2-equivalent impact of each practice relative to baseline, using GWP100 AR4 values (CH4 = 25, N2O = 298; IPCC 2007, WG1 Table 2.14). Negative values indicate a net climate benefit (reduced atmospheric forcing). SOC change annualized over the 8-year simulation period (2016–2024) and converted to CO2 mass (C \(\times\) 44/12). N2O and CH4 are annual flux deltas from baseline. CH4 contributions are ~0 Gg CO2e yr⁻¹ in all scenarios – negligible for non-flooded annual crops. Note: CO2e values represent maximum technical potential assuming full adoption across all modeled cropland; realized outcomes will depend on adoption rates and SOC saturation dynamics.
Scenario SOC (Gg CO2e yr⁻¹) N2O (Gg CO2e yr⁻¹) CH4 (Gg CO2e yr⁻¹) Net (Gg CO2e yr⁻¹)
Compost -6,256 -1,521 ~0 -7,777
Reduced Till -119 +3 ~0 -115
Zero Till -211 +21 ~0 -191
Drip Irrigation -1,675 +460 ~0 -1,215
Stacked (all) -8,563 -1,050 ~0 -9,613

Key Takeaways

Key Takeaways
  1. Compost and stacked practices deliver the largest net climate benefits (-7,777 and -9,613 Gg CO2e yr⁻¹ respectively). Both increase soil carbon and reduce N2O simultaneously.
  2. Drip irrigation provides a moderate net benefit (-1,215 Gg CO2e yr⁻¹). SOC gains outweigh N2O increases.
  3. Tillage reduction shows small but positive SOC gains. Zero till (+0.4% SOC, -191 Gg CO2e yr⁻¹) and reduced till (+0.2% SOC, -115 Gg CO2e yr⁻¹) both show modest net climate benefits. These small gains are consistent with the 8-year simulation period; meta-analyses indicate no-till SOC benefits become significant after >10 years of adoption (Six et al. 2004, Oecologia).
  4. CH4 is negligible for non-flooded annual croplands (~0 Gg CO2e yr⁻¹ in every scenario). CH4 will become meaningful when rice paddies are included in future model runs.
  5. N2O is a critical trade-off variable. Drip irrigation increases N2O (+12.0%) despite SOC benefits, reinforcing the need for multi-variable reporting. Compost reduces N2O (-39.5%), amplifying its SOC co-benefit.

How to Use This Atlas

Navigate using the sidebar or the links below. Each page is organized with tabsets for switching between scenarios and click-to-zoom on all figures.

Page What It Shows
Soil Carbon Atlas County-total and field-density maps for Total Soil Carbon across all scenarios, with difference maps
GHG Emissions Atlas N2O and CH4 emission maps – the critical trade-off analysis
Biomass Atlas Aboveground biomass maps (end-of-year annual crop standing biomass)
Model Drivers What environmental factors drive the spatial patterns? ALE/ICE diagnostics

Methods Overview

SIPNET (anchor sites)  -->  Random Forest  -->  Field predictions  -->  County aggregation  -->  Maps
     100 sites               8 predictors      ~132,000 fields        57 counties
     per scenario           (soil, climate,
                             topography, area)

Scenarios are based on NRCS conservation practice standards:

  • Baseline – Current farming practices (reference)
  • Compost – Organic amendment application (NRCS CPS 808)
  • Reduced Till – Reduced tillage intensity (NRCS CPS 345)
  • Zero Till – No-till farming (NRCS CPS 329)
  • Drip Irrigation – Conversion from flood/sprinkler to drip (water conservation + GHG reduction)
  • Stacked – All practices applied simultaneously

Scenario Definition

Table 1: Scenario parameters based on NRCS conservation practice standards. Simulation period: 2016–2024. Soil depth: 30 cm.
Scenario NRCS CPS Description Key Parameter Changes
Baseline – Current conventional practices Conventional tillage (STIR ~70), synthetic N (200 kg N ha⁻¹), sprinkler irrigation (540 mm season⁻¹)
Compost CPS 808 (CA-NRCS ICPS; national CPS 336) Organic amendment application 4.7 dry tons ac⁻¹ compost (C:N = 16), replaces synthetic N
Reduced Till CPS 345 Reduced soil disturbance STIR ~20, >30% surface residue maintained
Zero Till CPS 329 No mechanical disturbance STIR ≤ 20, 100% residue retained
Drip Irrigation CPS 441/449 Microirrigation system + water management Sub-canopy drip, 320 mm season⁻¹ (40% reduction from baseline)
Stacked 808 + 345 + 449 Combined practices Compost + reduced till + drip irrigation

Simulation period: 2016–2024. Soil carbon values are end-of-simulation cumulative stocks at 30 cm depth. GHG fluxes (N2O, CH4) are annual emission rates.

Model outputs:

  • TotSoilCarb – Total soil organic carbon to 30 cm depth (Mg C ha⁻¹ field density; Gg C county totals)
  • AGB – Aboveground biomass (Mg C ha⁻¹ field density; Gg C county totals)
  • N2O flux – Nitrous oxide emissions (kg N2O ha⁻¹ yr⁻¹ field density; Gg N2O yr⁻¹ county totals)
  • CH4 flux – Methane emissions (kg CH4 ha⁻¹ yr⁻¹ field density; Gg CH4 yr⁻¹ county totals)