Neglecting plant physiology: systematic overestimation of drought projections

Abstract
The impact of climate change on droughts is typically attributed to rising temperatures and altered precipitation patterns. Yet, most drought projections overlook a major climate-induced mechanism: the effect of elevated CO₂ on plant physiology, leading to a significant potential overestimation of droughts magnitudes and impacts. In fact, elevated CO₂ enhances biomass production and reduces stomatal conductance, thereby increasing water-use efficiency . Our systematic review reveals that nearly 90% of evapotranspiration-based drought projections omit CO₂-driven vegetation feedback, and only 10% acknowledge this limitation. Neglecting vegetation response to CO2 can overestimate future drought-affected areas by up to 17.4 ± 10.6% under high-emission scenarios (CO₂ > 900 ppm), and in some regions even reverse the projected direction of change. This widespread oversight can hamper the robustness of global drought projections. Accounting for vegetation–CO₂ interactions is therefore crucial to avoid systematic bias and produce reliable predictions of water availability in a warming world.