Original paper
A re-evaluation of evaporation measurements and calculations for inland waters based on physical considerations
Raabe, Armin; Holstein, Peter; Spank, Uwe
Meteorologische Zeitschrift (2026)
published online: Jan 22, 2026
manuscript accepted: Nov 26, 2025
final revised version received: Oct 13, 2025
manuscript revision requested: Jun 19, 2025
manuscript received: Jan 23, 2025
DOI: 10.1127/metz/1269
Open Access (paper may be downloaded free of charge)
Abstract
The correct model-based estimation of evaporation rates from water surfaces is crucial for an efficient water management of reservoirs and other water storages as well as for a successful implementation of flooding projects of former opencast mines, and a sustainable and economical operation of aquacultures. This study aims to model the daily evaporation and the diurnal course of evaporation rates from extensive open water surfaces and to compare and evaluate these model estimates using measured values from a floating evaporation pan and eddy covariance (EC) measurements. In particular, the reasons for the unavoidable differences between the model and measurement results, but also between the two comparative measurements methods used for the evaluation, are discussed and quantitatively assessed. Over the decades, various modelling approaches have been developed and proposed to estimate evaporation from water surfaces of different sizes (ranging from 1 m² to 106 m²). These methods include the DALTON, BULK, PENMAN, and ENERGY BALANCE approaches, each focusing on daily evaporation values. In this work, we use experimental data to compare and evaluate these modelling approaches with respect to their effectiveness in representing the daily course of evaporation and capturing the underlying physical processes. Our comparison of the DALTON and BULK approaches led to the development of a wind speed (u 2)-dependent DALTON number, CE , which can be integrated into the BULK method to better model the daily evaporation cycle. The proposed formulation for CE is: Additionally, we discuss the variability of CE with respect to the size of the water body. Our comparison between modelling and measurement results, but also between the EC data and the data of the direct evaporation measurements from a floating evaporation pan, revealed significant discrepancies. Specifically, evaporation estimates using the direct measurements can be up to 100% higher than those obtained from EC-measurements. These discrepancies cannot be attributed entirely to the well-known phenomenon of the energy-balance-closure gap, which is typically for EC measurements but is also very significantly and substantially caused by methodological limitations of the measurements using evaporation pans. Considering that floating evaporation pans have served as a reference for estimating water evaporation for decades, this methodological problem is not limited to our study, but also affects the modelling methods used to estimate open water evaporation in general.
Keywords
lake evaporation • evaporation pan measurements • eddy flux measurements • DALTON number estimates