Frederik Kratzert, Martin Gauch, Daniel Klotz, Grey Nearing 

Machine learning (ML) has an increasing role in the hydrological sciences, and in particular, certain types of time series modeling strategies are popular for rainfall-runoff modeling. A large majority of studies that use this type of model do not follow best practices, and there is one mistake in particular that is very common: training deep learning models on small, homogeneous data sets (i.e., data from one or a small number of watersheds). In this position paper, we argue why it is not a good idea to train a Long Short Term Memory (LSTM) model on data from a single watershed. Instead, deep learning streamflow models are best when trained with a large amount of hydrologically diverse data.