Analysing Flash Flood Hydrographs From Different Rainfall Temporal Profiles

ABSTRACT The temporal distribution of rainfall is a key driver of flood response. Yet, flood estimation methods are frequently based on symmetrical design profiles. Recent research using sub‐hourly rainfall data from Great Britain indicates that a significant proportion of observed rainfall events are non‐symmetrical. This paper investigates how different rainfall profiles affect river flow hydrographs for a set of small, flash‐flooding catchments. Results show that rainfall profiles affect observed hydrograph peak flow and timing. Most importantly, back‐loaded rainfall profiles lead to higher peak flows than symmetrical or front‐loaded profiles. These observations are compared to current design practice, using the Revitalised Flood Hydrograph (ReFH2.3) model to simulate flows from different rainfall profiles. Simulated events reproduce the observed response of peak magnitude but differ for peak time. A comparison of modelled flows with catchment descriptors indicates that steep, low permeability, wet catchments are most sensitive to rainfall profile shape. These are also the most vulnerable catchments to flash flooding. We recommend that different rainfall profile shapes should be considered for flood risk assessments in rapid response catchments, particularly since global warming is increasing the number of intense, short‐duration downpours.