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Design flood estimation and utility of high‐resolution calibration data in small, heavily urbanised catchments

Design flood estimates are often required for small, heavily urbanised catchments, which respond quickly to storm events. However, hydrological models are most frequently calibrated using daily or hourly data on larger, more rural catchments, which respond on much longer timescales. Here, we calibrate a lumped, conceptual rainfall‐runoff model (ReFH2) in three small (2–6 km2), heavily urbanised catchments in Swindon, UK, assessing the benefits of using high‐resolution temporal and spatial data. Modelling shows that heavy urbanisation does not by itself invalidate the applicability of a lumped, conceptual model. However, we find great dissimilarities between runoff behaviour in different heavily urbanised catchments, with some types behaving similarly to rural catchments. In other cases, response and contributing catchment area can depend more on underground topology than catchment topography. Calibrated runoff response is insensitive to the temporal resolution of the calibration events in all study catchments. Future research should aim to differentiate between different types of heavily urbanised catchment, potentially through landscape metrics to measure the connectivity and isolation of different land surface types.