Priestley and Taylor discuss the assessment of surface heat flux and evaporation using large-scale parameters. They emphasize that sensible and latent heat fluxes over land should be parameterized based on energetic considerations, while bulk aerodynamic formulas are more suitable over the sea. Data from various sites suggest a general formula for the relationship between sensible and latent heat fluxes. For drying land surfaces, evaporation is calculated using a formula with a factor that remains constant, followed by a linear decrease in evaporation rate. The paper explores the differences in heat flux and evaporation over land and oceans, highlighting the importance of surface temperature and dryness in determining these fluxes. It discusses the use of lysimeters and other measurements to estimate evaporation rates and the role of advection in influencing these rates. The authors also analyze the relationship between evaporation and potential evaporation, showing that the ratio of actual to potential evaporation decreases linearly with increasing water loss. The paper concludes that the value of α, a key parameter in estimating evaporation, is approximately 1.26 for saturated surfaces. This value is derived from various data sets, including observations from different locations and conditions. The authors emphasize the importance of understanding the dynamics of evaporation and heat flux in both land and ocean environments, and the need for accurate measurements and models to capture these processes. The study underscores the significance of considering both surface conditions and large-scale atmospheric dynamics in the assessment of surface heat flux and evaporation.Priestley and Taylor discuss the assessment of surface heat flux and evaporation using large-scale parameters. They emphasize that sensible and latent heat fluxes over land should be parameterized based on energetic considerations, while bulk aerodynamic formulas are more suitable over the sea. Data from various sites suggest a general formula for the relationship between sensible and latent heat fluxes. For drying land surfaces, evaporation is calculated using a formula with a factor that remains constant, followed by a linear decrease in evaporation rate. The paper explores the differences in heat flux and evaporation over land and oceans, highlighting the importance of surface temperature and dryness in determining these fluxes. It discusses the use of lysimeters and other measurements to estimate evaporation rates and the role of advection in influencing these rates. The authors also analyze the relationship between evaporation and potential evaporation, showing that the ratio of actual to potential evaporation decreases linearly with increasing water loss. The paper concludes that the value of α, a key parameter in estimating evaporation, is approximately 1.26 for saturated surfaces. This value is derived from various data sets, including observations from different locations and conditions. The authors emphasize the importance of understanding the dynamics of evaporation and heat flux in both land and ocean environments, and the need for accurate measurements and models to capture these processes. The study underscores the significance of considering both surface conditions and large-scale atmospheric dynamics in the assessment of surface heat flux and evaporation.