Thornthwaite-Holzman model for a wide range of daily evaporation rates

This study employs meteorological data from a weather station located in a coastal desert area in Kuwait, with a wide range of temperature, relative humidity, wind speed and evaporation measurements. The data have been used to test the well-known theoretical aerodynamic model of Thornthwaite-Holzman. The results show that the performance of this model is satisfactory for evaporation rates up to 10 mm/day, but there is an obvious systematic shift in accuracy beyond that from 10 to 40 mm/day. It is noted that the specific humidity difference proposed in the original model was assumed to have a linear correlation with evaporation rates. The study suggests modifying this assumption to become rather of a power form. The modification produced acceptable results based on subjective statistical criteria. This modification will help in extending our ability for analysing hydrological problems in different environments of high or low evaporation rates.