LAUSR

Abstract. Personification can be annoying, but also instructive. If a Rainfall-Runoff (RR) model was a hydrologist it could be called the Modelled Hydrologist, MH. Ideally, an MH used when tackling real–world problems such as flooding and climate change would be acquainted with hydrologic laws at the catchment scale and with a diverse panel of desk and field hydrologists who have between them thousands of years of experience. In practice, though, the MHs for RR models are largely ignorant of hydrology. Some of this ignorance is real (e.g. the hydrologic laws are unknown). The rest is selective ignorance, as is practised throughout science whenever there is a need for complex system analysis, parsimony, or similar. It is a form of designed neglect. In lumped RR modelling, the classic MH is that used in Jakeman and Hornberger’s experiment on their question “How much complexity is warranted in a rainfall–runoff model?”. Based on what that MH “knows” it is a statistician dilettante–hydrologist. When studying difficult and confusing problems (conundrums) like RR modelling it is helpful to have simple concrete examples to use as benchmarks and when generating hypotheses. Here, an MH for lumped modelling is built which is a layman with an interest in the weather and river flows (e.g. a river fisherman). The MH is created in a novel experiment in which statements of knowledge in everyday English are transformed systematically into a novel parameterless RR model. For a set of 38 UK catchments, the relative importance is measured as 1 and 6, respectively, for the layman’s knowledge about seasonality and wetness, and 2 for the knowledge that runoff records are always unpredictable to some degree. Hydrologic laws are discussed and hydrologic similarly in time and place is explored.