In a comprehensive synthesis published in the journal Carbon Research, lead author Nanthi Bolan and a global team of researchers examined the complex mechanisms through which climate-driven extreme weather alters soil organic carbon retention. Soil organic carbon serves as a primary marker for agricultural productivity, soil structural stability, and broader ecosystem functions. However, the intensification of floods, droughts, and wildfires worldwide has disrupted the delicate balance between plant carbon inputs and microbial decomposition. Depending on the specific environmental conditions and land management strategies in place, soils can either store carbon or act as a substantial source of greenhouse gas emissions.

Drought conditions create severe water limitations that restrict plant canopy development and lower overall biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More production. To cope with water scarcity, plants reallocate resources to expand their root networks, which shifts the composition of carbon entering the ground. While aboveground litterfall declines, root-derived inputs become the dominant source of organic material. These root systems generally possess higher carbon-to-nitrogen ratios, rendering them more resistant to rapid microbial decay. At the same time, prolonged dry spells lower overall microbial biomass and reduce litter decomposition rates by approximately 13 percent across various biomes. Heterotrophic soil respiration drops during dry conditions, allowing semi-decomposed organic matter and dissolved organic carbon to temporarily build up in topsoil layers. However, when rain eventually returns, a rapid surge in microbial activity causes a burst of carbon dioxide emissions that often erases any short-term carbon gains. Across multi-year drought cycles, total soil organic carbon storage ultimately falls, with grasslands and arable croplands experiencing reductions of roughly eight percent.

Flooding events alter soil carbon dynamics through distinct physical and chemical pathways. When excess water saturates the soil, oxygen availability drops rapidly, turning aerobic environments into anaerobic ones within a single day. This shift suppresses typical microbial respiration while prompting anaerobic bacteria to release gases such as methane and nitrous oxide. The influx of water mobilizes dissolved organic carbon, accelerating its movement through the soil profile and driving significant carbon losses via surface runoff and deep leachingLeaching is the process where nutrients are dissolved and carried away from the soil by water. This can lead to nutrient depletion and environmental pollution. Biochar can help reduce leaching by improving nutrient retention in the soil.   More. Frequent flooding in riparian zones and floodplains often decreases total soil carbon content compared to non-flooded areas. However, under specific conditions such as high salinity or continuous nutrient inputs, waterlogging can promote the accumulation of mineral-associated organic matter and microbial necromass, demonstrating that local soil conditions strongly dictate carbon retention outcomes.

Wildfires exert immediate and severe impacts on terrestrial carbon storage by directly burning surface vegetation and organic soil layers. High-severity fires can volatilize between 50 and 80 percent of topsoil organic carbon, removing the primary sources of fresh organic matter and interrupting root exudations. Soil heating destroys surface microbial communities and lowers overall extracellular enzyme activity by 20 to 40 percent. Despite these severe initial losses, fires also generate pyrogenic carbon, or char, through incomplete combustion. This black carbon resists biological breakdown and can remain stable in the soil for centuries, accounting for up to 15 percent of total organic carbon in fire-affected areas. As post-fire vegetation slowly recovers, pioneer species help restore root inputs, but full microbial and structural recovery can take anywhere from a decade to several centuries.

Source: Bolan, N., Messiga, A. J., Sharma, S., Mukherjee, S., Bolan, S., Salehin, S. M. U., Rupngam, T., Rajan, N., Zhang, T., Yang, Y., Jagadesh, M., & Siddique, K. H. M. (2026). Impacts of climate change-induced extreme weather events on carbon dynamics in soil. Carbon Research, 5(1), Article 58.