Energy versus aerodynamic controls of reference evapotranspiration: a multi-regional assessment across Brazilian climate typologies

Abstract Reference evapotranspiration (ETo) constitutes a determining variable in hydroclimatic studies and is frequently estimated using empirical methods whose accuracy is conditioned by the local climatic regime. This study investigated the hierarchy of meteorological elements associated with ETo variability (Penman–Monteith FAO-56) in six Brazilian municipalities with contrasting climate typologies. Long-term meteorological data (1990–2019) were used and processed through path analysis at annual and seasonal scales to decompose the effects of solar radiation, temperature, relative humidity, and wind speed. Path models explained a high proportion of ETo variability across all locations (R² ranging from 0.977 to 0.995). The results showed that the hierarchy of direct effects on ETo is governed by climatic context and seasonality, with no universal driver of evaporative demand identified across the analyzed locations. Solar radiation and wind speed were the dominant contributors to ETo variability, alternating in prominence among sites, while relative humidity exhibited consistent negative direct effects. Mean air temperature exerted secondary influence in most evaluated scenarios. At the seasonal scale, a systematic reconfiguration of radiative and aerodynamic controls was observed, highlighting the dynamic nature of ETo. The findings suggest potential limitations of exclusively temperature-based approaches in environments where radiative or aerodynamic drivers predominate. This diagnosis contributes to a more rigorous selection of estimation methods and reinforces the need for multivariate and physically consistent models for water management under contrasting climatic regimes.