Assessing the contribution of elevated CO₂–induced surface resistance changes to referenceevapotranspiration trends over South Asia

The impact of increasing CO₂ concentration under global warming includes altered surface energy balance, plant physiology and atmospheric moisture demand, which influences evaporative stress. We aim to attribute the impact of increasing CO₂ concentration to the projected changes in reference evapotranspiration (ETo) under multiple climatic change scenarios over South Asia. We use second order Taylor series expansion to quantify the contribution of CO₂ using modified penman monteith equation, where surface resistance is estimated as a function of CO₂ concentration. The attribution framework enables assessment of scenario dependent CO₂ impact on future aridity, water availability, water resource planning and agricultural adaptation.