Abstract
Abstract 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.
Highlights
It is expected that anthropogenic climate change will intensify the global hydrological cycle as the world continues to warm (IPCC ), thereby increasing the frequency and severity of extremes such as floods (Hirabayashi et al ) and droughts (Prudhomme et al ), strong regional variability and uncertainties in projections exist (Arnell & Gosling )
Given inherent uncertainties introduced through the climate-hydrology modelling chain, and the complex and still poorly understood role of catchments in modifying climate signals, observations remain the foundation for any scientific understanding on climate change impacts on river flows, when justifying costly adaptation plans
The second aim of this paper is to develop a standardised trend analysis procedure to apply routinely to the Benchmark Network, based on established methods within the hydroclimatic literature, with a first application on the newly designated UKBN2 dataset
Summary
It is expected that anthropogenic climate change will intensify the global hydrological cycle as the world continues to warm (IPCC ), thereby increasing the frequency and severity of extremes such as floods (Hirabayashi et al ) and droughts (Prudhomme et al ), strong regional variability and uncertainties in projections exist (Arnell & Gosling ). The recent UK Climate Change Risk Assessment report (ASC ) identified both increased. The notable hydrological volatility experienced in the early decades of the 21st century (Hannaford ; for a fuller description of these episodes see the National River Flow Archive (NRFA) website: http://nrfa.ceh.ac.uk/occasional-reports) has exposed the UK’s vulnerability to hydrological extremes and there is a clear scientific and socio-economic need to understand the changing nature of these extremes. Given inherent uncertainties introduced through the climate-hydrology modelling chain, and the complex and still poorly understood role of catchments in modifying climate signals, observations remain the foundation for any scientific understanding on climate change impacts on river flows, when justifying costly adaptation plans. Disentangling the many interacting drivers of change in river flows is a major research challenge, but a first step is using river flow data that are sensitive to climatedriven changes
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