Terrestrial vegetation absorbs roughly 120–149 petagrams of carbon annually through photosynthesis, offsetting about one-third of global fossil-fuel emissions. Precipitation is a primary driver of vegetation growth and productivity, yet how ecosystems respond to rainfall variability—termed vegetation sensitivity to precipitation (Sppt)—remains poorly understood under the growing frequency of compound disturbances. While droughts and wildfires are known to independently affect carbon and water cycles, their combined impacts on Sppt have not been systematically quantified at the global scale. Based on these challenges, or due to these unresolved interactions, there is a critical need to conduct in-depth research on how compound drought–fire events alter the functional dependence of ecosystems on precipitation and carbon–water coupling.
On August 3, 2026, researchers from Tongji University published (DOI: 10.34133/remotesensing.1060) a study in the Journal of Remote Sensing examining how compound drought–fire events affect vegetation sensitivity to precipitation. Using global satellite observations from 2001 to 2022, the team tackled a pressing real-world challenge: as climate change intensifies both droughts and wildfires, ecosystems face simultaneous stressors whose combined effects on carbon uptake and water use remain largely unknown. This research provides the first disturbance-oriented global assessment of how these compound events reshape the fundamental relationship between vegetation photosynthesis and rainfall.
The study uncovered three major breakthroughs. First, although global vegetation sensitivity to precipitation declined from 2001 to 2022, it actually increased significantly within 1–3 years after compound drought–fire events—rising more sharply than after droughts alone. Second, hydrological drought–fire events produced stronger effects than meteorological drought–fire combinations, with larger burned areas and greater sensitivity enhancement. Third, using an interpretable machine-learning model, the team identified atmospheric aridity (vapor pressure deficit) and soil nutrients—particularly nitrogen and phosphorus—as key drivers of this increased sensitivity. Critically, the elevated Sppt was accompanied by widespread reduction in water-use efficiency, signaling a potential decoupling of carbon and water processes that may compromise ecosystem resilience under future climate regimes.
The team analyzed three satellite-derived vegetation proxies: solar-induced chlorophyll fluorescence (SIF), normalized difference vegetation index (NDVI), and enhanced vegetation index (EVI). They identified 72,088 compound meteorological drought–fire events and 108,373 compound hydrological drought–fire events globally between 2001 and 2022, with spatial overlap of approximately 62.5% between event types. Using a 3-year moving-window multiple linear regression incorporating precipitation and temperature, they calculated pixel-wise Sppt values. Results showed that Sppt increased by 4.79×10⁻⁵ mm⁻¹ (SIF-based) one year after compound events, rising to 4.86×10⁻⁵ mm⁻¹ at three years. Hydrological drought–fire events drove stronger increases (7.89×10⁻⁵ mm⁻¹ for SIF) than meteorological combinations (3.20×10⁻⁵ mm⁻¹). The random forest model explained 79% of spatial variation in Sppt changes, with vapor pressure deficit change, soil phosphorus, and soil nitrogen ranking among the top predictors. Importantly, 54.6% of vegetated areas showed increased Sppt post-disturbance, yet most regions exhibited declining water-use efficiency—revealing a widespread carbon–water decoupling phenomenon across diverse ecosystems.
“Our findings reveal a critical vulnerability: after compound drought–fire events, ecosystems become more dependent on rainfall but less efficient at converting water into carbon gain,” said Professor Qunming Wang, corresponding author. “This decoupling suggests that vegetation may be entering a fragile recovery state, where increased rain sensitivity does not translate into healthier carbon–water balance—a warning signal for ecosystem resilience under escalating climate extremes.”
The researchers utilized ESA’s FireCCI burned-area dataset, SPEI drought indices, and GRACE terrestrial water storage data. Vegetation indices came from MODIS products, while SIF data were sourced from the National Tibetan Plateau Data Center. They applied seasonal-trend decomposition to remove long-term effects, then performed pixel-wise multiple linear regressions with 3-year moving windows. Only isolated events with 3-year disturbance-free intervals were included. Baseline Sppt was established using 36 months pre-event, with changes calculated as post-event minus baseline values. Statistical significance was assessed via Mann–Kendall tests and Mann–Whitney U tests across IPCC reference regions.
This research opens new pathways for early-warning systems that monitor ecosystem vulnerability after compound disturbances. By identifying vapor pressure deficit and soil nutrients as key sensitivity drivers, the findings can guide targeted restoration efforts and improve Earth system models’ predictions of carbon-cycle feedbacks. As compound drought–fire events become more frequent, this framework could help policymakers prioritize regions at risk of carbon–water decoupling, ultimately supporting more climate-resilient land management strategies. Integrating radar and LiDAR observations may further refine Sppt estimates in future studies, enhancing our ability to safeguard terrestrial carbon sinks.
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References
DOI
10.34133/remotesensing.1060
Original Source URL
https://spj.science.org/doi/10.34133/remotesensing.1060
Funding Information
H.X. and Q.W. were supported by the National Natural Science Foundation of China under Grants 42222108 and 42171345.
About Journal of Remote Sensing
The Journal of Remote Sensing, an online-only Open Access journal published in association with AIR-CAS, promotes the theory, science, and technology of remote sensing, as well as interdisciplinary research within earth and information science.