A Method for Identifying Rainfall‐Runoff Events at Sub‐Hourly Time Scales: Applications for Nature‐Based Solutions and Water Resources

ABSTRACT Understanding how changes in catchment conditions affect ecohydrology in response to rainfall‐runoff events is crucial when developing informed strategies to enhance flow resilience, restore natural habitats, interpret water quality data or reduce flood risk. This can be undertaken through evaluation of impacts on peak flows or flow attenuation within headwater to meso‐scale catchments, extracting rainfall‐runoff events from sub‐hourly flow and rain timeseries data. Where sub‐hourly insight is needed due to the scale of headwater catchments and their rapid flow response. Detailed documentation of a standardised event extraction methodology for sub‐hourly flow time series and its applications is limited, and existing common methods have the potential to introduce bias. To address these needs, we present a methodology for event extraction alongside case studies detailing how it has been used to evidence change in hydrological function in relation to several restoration strategies and catchment intervention measures. A workflow is outlined for the delineation and extraction of rainfall‐runoff event periods linking key hydrograph metrics, such as antecedent conditions and lag‐times, using sub‐hourly rainfall and flow observations. Across the case studies, noticeable impact was seen, with peatland restoration reducing peak flows by 49%, leaky dams and beaver dams reducing peak flows by 23% and importantly for water quality, showing that catchment measures which attenuate flows and reduce stormflow peaks can be very beneficial. The outputs of this work have had real world impact, informing catchment management strategies, demonstrating the value of a systematic approach that could be widely adopted across catchments of different typologies.