Technical note: Pitfalls in using log-transformed flows within the KGE criterion
Note technique: Pièges dans l'utilisation du log dans la transformation des débits pour le critère KGE
Santos, L. ; Thirel, G. ; Perrin, C.
Type de document
Article de revue scientifique à comité de lecture
Affiliation de l'auteur
IRSTEA ANTONY HYCAR FRA ; IRSTEA ANTONY HYCAR FRA ; IRSTEA ANTONY HYCAR FRA
Résumé / Abstract
Log-transformed discharge is often used to calculate performance criteria to better focus on low flows. This prior transformation limits the heteroscedasticity of model residuals and was largely applied in criteria based on squared residuals, like the Nash-Sutcliffe efficiency (NSE). In the recent years, NSE has been shown to have mathematical limitations and the Kling-Gupta efficiency (KGE) was proposed as an alternative to provide more balance between the expected qualities of a model (namely representing the water balance, flow variability and correlation). As in the case of NSE, several authors used the KGE criterion (or its improved version KGE′) with a prior logarithmic transformation on flows. However, we show that the use of this transformation is not adapted to the case of the KGE (or KGE′) criterion and may lead to several numerical issues, potentially resulting in a biased evaluation of model performance. We present the theoretical underpinning aspects of these issues and concrete modelling examples, showing that KGE′ computed on log-transformed flows should be avoided. Alternatives are discussed.
Hydrology and Earth System Sciences, vol. 22, p. 4583 - 4591