A Comprehensive Review: Climate Change Impacts on Reference Evapotranspiration (ET0)

Reference Evapotranspiration (ET0) is a key component of the hydrological cycle and strongly influenced by climate variability, land use change, and anthropogenic activities. Accurate ET0 estimation is vital for water resource management, irrigation planning, and climate adaptation strategies. This review synthesizes findings from global studies spanning 2000–2025, covering agricultural systems, wetlands, lakes, and urban environments. Traditional estimation methods such as the FAO-56 Penman–Monteith model remain the standard, while empirical, energy balance, and machine learning approaches offer useful alternatives when data are limited. Remote sensing advances have improved spatiotemporal monitoring, yet challenges remain in calibration, validation, and uncertainty management. The reviewed literature highlights that ET0 trends are highly sensitive to factors such as sunshine duration, wind speed, and vegetation cover, with marked regional variability. Urbanization and impervious surface expansion further intensify ET0 fluctuations by enhancing heat island effects. Research gaps include short-duration datasets, limited interdisciplinary integration, and uncertainties in large-scale modelling. Future directions emphasize hybrid modelling, long-term climate records, and improved satellite-based observations to strengthen ET0 predictions under climate change scenarios.