Characterizing Anthropogenic Modification of Root Zone Storage Capacity

Vegetation plays a crucial role in regulating the water cycle through transpiration, which is influenced by the root zone storage capacity (S_R). S_R is dynamically influenced by climate, land use, and vegetation, with ecosystems adapting to environmental changes by modulating S_R. Human interventions, such as deforestation, agriculture, and irrigation, significantly alter S_R by changing vegetation cover and water availability. This study aims to quantify human-induced modifications to S_R at global scale. Through a lens of human domination, we highlight the repurposing of S_R and its implications for ecosystem resilience.

A random forest model was developed to estimate S_R based on climate, land and vegetation related variables, trained on available present-day estimates of S_R derived from process-based methods. By substituting actual vegetation with potential natural vegetation (PNV) and altering climate variables to reflect preindustrial, present, and future conditions, we assess the impact of land use change and climate change on S_R.

Under current land use, average S_R is approximately 7.5 mm lower than in the PNV scenario, assuming the same climate conditions. In future extreme warming scenarios (RCP8.5), S_R requirements are projected to increase from about 136 mm to 243 mm, which is deemed unrealistic, suggesting potential transgression of limits to root zone adaptation in ecosystems.

These findings underscore the significant and widespread anthropogenic modification of root zone storage capacity, and point at risks for ecosystem resilience loss in regions where climate change outpaces adaptive capacity. We call for more systematic and observation-based studies to understand these dynamics better.