Widespread and systematic effects of fire on plant-soil water relations

Wildfire activity and the hydrological cycle are strongly interlinked. While it is well known that wildfire occurrence and intensity are controlled by water availability, less is known about the effects of wildfire on plant and soil water cycling, especially at large scales. Here we investigate this by analyzing fire impacts on the coupling between plant and soil water budgets, at the global scale, using remote sensing of soil moisture, vegetation water content and burned area. We find a strong effect of fire on plant-soil water relations, accelerating soil moisture loss by 17% and leading to faster gains in vegetation water content by 62%, both of which are positively related to fire severity and largest in forests. This effect is spatially extensive, with accelerated soil moisture loss found in 67%, and increased vegetation water content gain found in 67% of all analyzed burned areas. After fire, vegetation also tended to have less control on their water content (i.e., were more anisohydric). In summary, fire changes ecosystem functioning by increasing ecosystem water losses and shifting the relationship between soil and vegetation water budgets. With climate change, wildfire is likely to play an increasingly important role in ecosystem water cycling and subsequent ecosystem recovery.