Accounting for soil moisture in rainfall-runoff modelling of urban areas

An important challenge in hydrology is the quantification of the effect of urbanisation on rainfall-runoff processes. Many existing hydrological models assume a constant percentage runoff from urban areas disconnected from soil moisture which is contrary to evidence from observational studies. The aim of this study is to explore if linking soil moisture and urban runoff generation can improve rainfall-runoff simulations. Two new conceptual representations (models) are introduced to account for hydrological effects of urban land including the introduction of a dynamic link between runoff and soil moisture. The first model uses a constant percentage runoff that will change from catchment to catchment. The second model explicitly links soil moisture and runoff from urban areas. The results show that the model with an explicit link to soil moisture performed 12% better than the fixed percentage model across 28 urban catchments located in the United Kingdom. For peak flows in highly urbanised catchments the linked model performed 17% better than the fixed percentage model.