The dynamic response of vegetation water use efficiency to wildfire disturbances in the Northern Hemisphere

Xi, H. and Wang, Q. and Atkinson, P.M. (2026) The dynamic response of vegetation water use efficiency to wildfire disturbances in the Northern Hemisphere. Agricultural and Forest Meteorology, 381: 111098. ISSN 0168-1923

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Abstract

Vegetation water use efficiency (WUE) serves as a critical indicator reflecting the interactions between ecosystem carbon and water cycles. However, rapid warming in the Northern Hemisphere and increasing wildfire activities have introduced significant disturbances, and potentially affected the dynamic changes in WUE that occur post-fire. Understanding these impacts is crucial for advancing our knowledge of ecosystem responses to environmental changes. In this research, we focused on analyzing the post-fire trajectories and response mechanisms of WUE during the growing season in the Northern Hemisphere by employing detrended and de-seasonalized WUE data combined with fire intensity derived from the moderate resolution imaging spectroradiometer. Our findings reveal that since 2001, the WUE of vegetation in the Northern Hemisphere during the growing season exhibited an overall downward trend (-0.016 g C m⁻² mm⁻¹ yr⁻¹), with a pronounced turning point observed around 2011, which may be related to large-scale climate anomalies, such as the strong La Niña event. Within five years after fire, 74.2% of ∆WUE (defined as post-fire WUE minus pre-fire WUE) values fell within the range of -0.5 to 0.5 g C m⁻² mm⁻¹ and showing a clear bias toward negative values, indicating that fire disturbances tended to produce adverse impacts on WUE. Notably, coniferous forests exhibited increasing WUE trends post-fire, whereas broadleaf forests tended to decline, with their trajectories further influenced by climatic zones. Machine learning-based attribution analysis highlighted that the pre-fire levels of WUE was a key factor influencing post-fire changes in WUE. Additionally, climate variables such as temperature, vapor pressure deficit, soil moisture, and precipitation also played important roles, these climatic drivers contributed significantly at local scales. Our study reveals post-fire trajectories of WUE among different vegetation types and identifies the primary drivers. These findings provide important insights for understanding coupled carbon-water cycle responses of northern vegetation to fire disturbance.