1,2,3,4,1,2- 1Institute of Geo-Hydroinformatics, Hamburg University of Technology, Hamburg, Germany
- 2United Nations University Hub on Engineering to Face Climate Change at the Hamburg University of Technology, United Nations University Institute for Water, Environment and Health (UNU-INWEH), Hamburg, Germany
- 3UK Centre for Ecology & Hydrology, Bangor, UK
- 4European Commission, Joint Research Centre (JRC), Ispra, Italy
Soil organic carbon (SOC) plays a central role in regulating soil fertility, water retention, and quantifying risks of soil degradation (Afshar et al., 2025). While climate variability is increasingly recognized as a major pressure on SOC, large-scale assessments of drought impacts on forest soils remain limited. Recent studies emphasize that drought effects on SOC are highly context dependent, shaped by soil carbon status, climate regime, and interacting environmental controls, calling for flexible modeling frameworks that can capture nonlinear responses (Hassani et al., 2024; Shokri et al., 2025).
In this study, we analyze SOC change between 2009 and 2018 across European forest soils using generalized additive models (GAMs) applied to harmonized LUCAS topsoil observations. SOC change is modelled as a nonlinear function of initial SOC, drought characteristics derived from the Standardized Precipitation Evapotranspiration Index (SPEI), climate, and soil properties.
GAM results show that drought severity exerts a significant, nonlinear impact on SOC change (p < 0.001), strongly modulated by initial SOC and climatic parameters. On average, under severe drought conditions, SOC declines by ~32% relative to mild drought conditions. Overall, the results demonstrate that drought impacts on forest SOC are state-dependent and spatially heterogeneous, governed by the combined influence of drought severity, initial carbon stocks, and regional climate conditions.
References:
- Afshar, M. H., Hassani, A., Aminzadeh, M., Borrelli, P., Panagos, P., Robinson, D. A., Or, D., & Shokri, N. (2025). Spatial and temporal assessment of soil degradation risk in Europe. Scientific reports, 15, 44636. https://doi.org/10.1038/s41598-025-33318-7
- Hassani, A., Smith, P., & Shokri, N. (2024). Negative correlation between soil salinity and soil organic carbon variability. Proceedings of the National Academy of Sciences, 121(18), e2317332121. https://doi.org/10.1073/pnas.2317332121
- Shokri, N., Robinson, D. A., Afshar, et al. (2025). Rethinking global soil degradation: Drivers, impacts, and solutions. Reviews of geophysics, 63(4), e2025RG000883. https://doi.org/10.1029/2025RG000883
How to cite: H. Afshar, M., Robinson, D. A., Panagos, P., and Shokri, N.: How Drought Influences Forest Soil Organic Carbon, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13105, https://doi.org/10.5194/egusphere-egu26-13105, 2026.
