Mimicry of a hydrological conceptual model (HBV): what's in a name?

Models that mimic an original model might have a different model structure that affects model output. This study assesses model structure differences and their impact on output by comparing 7 model implementations that carry the name HBV. We explained and quantified output differences with individual model structure components at both the numerical and mathematical level. It was found that none of the numerical and mathematical formulations of the mimicking models were (originally) the same as the benchmark, HBV-light. This led to small but distinct output differences for numerical implementations, and major output differences due to mathematical differences, although differences decreased after calibration. We argue that the lack of systematic model naming has led to a diverging concept of the HBV-model, diminishing the concept of model mimicry. Development of a systematic model naming framework, open accessible model code and more elaborate model descriptions are suggested to enhance model mimicry.