Designation and trend analysis of the updated UK Benchmark Network of river flow stations: the UKBN2 dataset

Observational trend analysis is fundamental for tracking emerging changes in river flows and placing extreme events in their longer-term historical context, particularly as climate change is expected to intensify the hydrological cycle. However, human disturbance within catchments can introduce artificial changes and confound any underlying climate-driven signal. The UK Benchmark Network (UKBN), designated in the early 2000s, comprised a subset of National River Flow Archive (NRFA) stations that were considered near-natural and thus appropriate for identification and interpretation of climate-driven hydrological trends. Here, the original network was reviewed and updated, resulting in the UKBN2 dataset consisting of 146 near-natural catchments. Additionally, the UKBN2 provides user guidance on the suitability of each station for the assessment of low, medium, and high flows. A trend analysis was performed on the updated UKBN2 dataset and results show that while the strength and direction of changes are dependent on the period of record selected, previously detected patterns of river flow change in the UK remain robust for longer periods (>50 years), despite the recent prevalence of extremes. Such a quality assured observational dataset will provide a foundation for future scientific efforts to better understand the changing nature of the hydrological cycle.