ORIGINAL RESEARCH article
Front. Water
Sec. Water and Climate
Volume 7 - 2025 | doi: 10.3389/frwa.2025.1597728
Overestimation of evapotranspiration across India if not considering the impact of rising atmospheric CO2
Provisionally accepted
- 1Environmental Sciences and Sustainable Engineering Centre, Indian Institute of Technology Palakkad, Palakkad, India
- 2Department of Computer Science and Engineering, Indian Institute of Technology Palakkad, Palakkad, India
- 3Department of Biotechnology, National Institute of Technology Raipur, Raipur, Chhattisgarh, India
- 4University of Illinois at Urbana-Champaign, Champaign, Illinois, United States
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The widely used FAO Penman-Monteith (FAO-PM) equation does not account for rising atmospheric CO2, which is known to reduce stomatal conductance that can lead to overestimation of reference evapotranspiration (ETo) in climate impact studies. We proposed a modified version of the FAO-PM equation that considers the impact of CO2 concentration on stomatal behavior and, consequently, on ETo. Comparing ETo estimates from the original and modified equations for India under SSP5-8.5 showed differences of 0.11-to-1.29 mm day -1 (2021-2030), 0.09-to-1.9 mm day -1 (2051-2060), and 0.17-to-3.14 mm day -1 (2091-2100). Under SSP1-2.6, differences were 0.12-to-1.26 mm day -1 , 0.12-to-1.47 mm day -1 , and 0.11-to-1.38 mm day -1 , respectively.Seasonal impacts were highest in the pre-monsoon, reaching 0.12-to-3.90 mm day -1 under SSP5-8.5 and 0.14-to-1.74 mm day -1 under SSP1-2.6. Ignoring CO2 effects could overestimate ETo by ~29% under SSP5-8.5 by 2100, leading to questionable predictions of droughts, heatwaves, and water demands. However, impact of CO2 was moderate under SSP1-2.6 resulting in ETo overpredictions of only 13%.
Keywords: evapotranspiration, FAO Penman-Monteith, Stomatal conductance, regional climate in India, Water Resources, elevated CO2
Received: 21 Mar 2025; Accepted: 08 Sep 2025.
Copyright: © 2025 Surendran, Sunil, Pahari, He and Jaiswal. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Deepak Jaiswal, Environmental Sciences and Sustainable Engineering Centre, Indian Institute of Technology Palakkad, Palakkad, India
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