Investigating the Role of Driving Variables on ETo Variability and “Evapotranspiration Paradox” Across the Indian Subcontinent Under Historic and Future Climate Change

• Published in: Water resources management 2024-11, Vol.38 (14), p.5723-5737
• Main Authors: Varghese, Femin C., Mitra, Subhasis
• Format: Article
• Language: English
• Subjects: Aridity; Atmospheric Sciences; Carbon dioxide; Civil Engineering; climate; Climate change; Drought; dry environmental conditions; Earth and Environmental Science; Earth Sciences; Environment; Evapotranspiration; Geotechnical Engineering & Applied Earth Sciences; Hydrogeology; Hydrology/Water Resources; India; Irrigation water; Least squares method; Net radiation; Paradoxes; Radiation; Radiation balance; Surface resistance; temperature; Trends; Variability; Water consumption; Water use; water utilization; Wind speed
• ISSN: 0920-4741; 1573-1650
• DOI: 10.1007/s11269-024-03931-8

Comprehensive studies on aridity, reference evapotranspiration (ETo) and their driving variables are lacking in the context of the Indian region. This study comprehensively analyzes the spatio-temporal trends in aridity, ETo and the driving variables across different zones over the Indian subcontinent under historic and future climate change. ETo is estimated based on the Penman-Monteith (PM) and a modified PM method incorporating CO 2 levels (PM-CO2) that takes into consideration the influence of CO 2 on surface resistance. Additionally, the partial least squares regression (PLSR) is employed to assess the relative contributions of the different climate variables to ETo trends and investigate the existence of the “evapotranspiration paradox” over the Indian region. The findings reveal that a substantial portion of the subcontinent has experienced a decline in annual ETo (70%) and aridity over the historical period. Under climate change projections ETo diverge considerably based on PM and PM-CO2 approach with PM projecting higher ETo across the region. Contribution analysis outcomes show temperature and net radiation are the most influential factors affecting ETo variability under both the historic and future periods. Furthermore, results also show the existence of the “evapotranspiration paradox” over majority of the region under historic conditions which is found to be diminishing under future climate change. The paradox in the historic period is explained by reductions in net radiation and wind speed dominating the increases in temperatures across the region. Outcomes from the study have implications towards future irrigation water usage and drought projections over the Indian subcontinent. Highlights Decreasing ETo trends across majority of study area over the historic period. Temperature and net radiation are the primary drivers of ETo variability under both historic and climate change scenario. ‘Evapotranspiration Paradox’ exists under historic period and is found to be diminishing under climate change.