When extreme weather rewrites the soil carbon cycle

A critical review led by Professor Nanthi Bolan maps how climate-induced extreme weather events, specifically drought, flooding, and wildfire, alter carbon inputs, microbial decomposition, and carbon sequestration in terrestrial soils

Published in Carbon Research, the study synthesises literature across terrestrial and aquatic interfaces to outline how compound weather disturbances jeopardise soil organic carbon storage and agricultural stability.

Systematic screening and review methodology

The authors conducted a structured bibliometric and qualitative review across major databases (Google Scholar, PubMed, and Web of Science):

• Literature pool:

  • An initial retrieval of 14,218 records was narrowed down through eligibility screening to 3,754 articles for bibliometric mapping via VOSviewer.

• Core synthesis cohort:

  • A focused subset of 187 high-impact publications was selected for detailed synthesis based on methodological rigour and relevance to soil carbon dynamics.

Mechanisms of weather-driven carbon mobilisation

The review details how distinct extreme weather phenomena alter the physical, chemical, and biological drivers of the soil carbon cycle:

Drought

Prolonged moisture deficits reduce plant biomass and overall carbon inputs to the soil. While plants may temporarily shift carbon allocation toward root systems, multiyear droughts suppress microbial biomass and litter decomposition.

Subsequent rewetting events often trigger rapid “CO₂ pulses” as suppressed microorganisms rapidly metabolise accumulated organic substrates, leading to net carbon loss, particularly in grasslands and arable croplands.

Flooding

Waterlogging creates anoxic conditions that restrict oxygen diffusion, shifting microbial metabolism toward anaerobic pathways. Prolonged saturation promotes the reductive dissolution of iron oxyhydroxides, releasing previously mineral-bound dissolved organic carbon (DOC).

Additionally, flood-induced erosion and leaching transport significant quantities of soil organic carbon into aquatic systems.

Wildfire

Combustion causes immediate loss of vegetation, surface litter, and soil organic matter. High-severity fires increase soil hydrophobicity (water repellency), alter microbial community structures, and expose protected carbon pools to accelerated erosion.

While incomplete combustion forms persistent pyrogenic carbon (biochar-like matter), the net carbon balance depends heavily on post-fire vegetation recovery and fuel load.

Key factors and research priorities

The authors emphasise that extreme weather impacts are heavily moderated by local land use, soil mineralogy, hydrology, and microbial diversity. Furthermore, compound events, such as severe drought followed immediately by intense flooding or wildfire, produce non-linear carbon losses that isolated-event analyses cannot predict.

To improve soil carbon stewardship and predictive modelling, the review recommends:

1. Harmonising measurement protocols for carbon pool shifts and microbial functional diversity across long temporal scales.
2. Investigating carbon stabilisation interactions involving iron and aluminium oxyhydroxides and clay-mineral protection matrices.
3. Combining high-resolution remote sensing, spectroscopy, and molecular genomic analyses to monitor carbon vulnerability under compound extreme events.