Climate-driven changes in UK river flows: a review of the evidence

There is a burgeoning international literature on hydro-climatic trend detection, motivated by the need to detect and interpret any emerging changes in river flows associated with anthropogenic climate change. The UK has a particularly strong evidence base in this area thanks to a well-developed monitoring programme and a wealth of studies published over the last twenty years. This paper reviews this research, with a view to assessing the evidence for climate change influences on UK river flow, including floods and droughts. This assessment is of international relevance given the scale of the research effort in the UK, a densely monitored and data-rich environment, but one with significant human disturbances to river flow regimes, as in many parts of the world. The review finds that changes can be detected in river flow regimes, some of which agree with future change projections, whilst others are in apparent contradiction. Observed changes generally cannot be attributed to climate change, largely due to the fact that river flow records are limited in length and short-term trends are confounded by natural variability. A UK ‘Benchmark’ network of near-natural catchments is an internationally significant example of an initiative to enable climate variability to be discerned from direct human disturbances (e.g. abstractions, dam construction). Generally, however, the problem of attribution has been tackled rather indirectly in the UK, as elsewhere, and more efforts are required to attribute change in a more rigorous manner

Hydrological Summary for the UK: April 2009

The monthly summary of hydrological conditions in the United Kingdom is compiled as part of the National Hydrological Monitoring Programme (a joint CEH and BGS enterprise). The report features contemporary data for rainfall, river flow, reservoir and groundwater levels in the form of maps and graphs. A commentary is provided on the status of the nation's water resources and any notable hydrological events during the month. The National River Flow and National Groundwater Level Archives help provide an historical context for these contemporary assessments. Financial support for the production of the Hydrological Summaries is provided by Defra, the Environment Agency, the Scottish Environment Protection Agency, the Rivers Agency in Northern Ireland and the Office of Water Services

Developing best practice for infilling daily river flow data

Complete river flow time series are indispensable to the sustainable management of water resources and even very short gaps can severely compromise data utility. Suitably-flagged flow estimates, derived via judicious infilling, are thus highly beneficial. The UK National River Flow Archive provides stewardship of and access to daily river flow records from over 1500 gauging stations and, whilst the majority are sensibly complete, historical validation reveals a significant quantity of gaps. A full assessment of the suitability of existing techniques for infilling such gaps is lacking. This paper therefore presents an appraisal of various simple infilling techniques, including regression, scaling and equipercentile analysis, according to their ability to generate daily flow estimates for 25 representative UK gauging stations. All of the techniques rely upon data transfer from donor stations and results reveal that the equipercentile and multiple regression approaches perform best. Case studies offer further insight and an example of infilling is presented, along with areas of future study. The results demonstrate the potential for developing generic infilling methodologies to ensure a consistent and auditable approach towards infilling, which could find wider application both within the UK and internationally

The July 2007 floods in England and Wales - a preliminary appraisal issued by the Centre for Ecology & Hydrology

The weather conditions experienced across much of the UK throughout the summer of 2007 have been truly exceptional. The jet stream (which influences the paths taken by weather systems in the North Atlantic) has followed an abnormally southerly track and the extension of the Azores high pressure cell across the UK – which brings settled weather conditions in most summers – has failed to become established. Correspondingly, a sustained sequence of rain-bearing low pressure systems has produced outstanding 12-week rainfall totals, and a series of flood events culminating in widespread severe flooding in late July

The 2010-12 drought and subsequent extensive flooding: a remarkable hydrological transformation

Across most of the UK, the 2010‑12 period was remarkable in climatic terms with exceptional departures from normal rainfall, runoff and aquifer recharge patterns. Generalising broadly, drought conditions developed through 2010, intensified during 2011 and were severe across much of England & Wales by the early spring of 2012. Record late spring and summer rainfall then triggered a hydrological transformation that has no close modern parallel. Seasonally extreme river flows were common through the summer, heralding further extensive flooding during the autumn and, particularly, the early winter when record runoff at the national scale provided a culmination to the wettest nine‑month sequence for England & Wales in an instrumental record beginning in 1766. This report provides comprehensive documentation and hydrometeorological appraisals of a three‑year period which incorporated a number of important regional drought episodes as well as the outstanding runoff and recharge patterns which characterised most of 2012. An examination of the wide range of impacts of the drought and flood episodes is included and the extreme hydrometeorological conditions are examined within an extended historical context. Finally, the recent exceptional conditions are reviewed in the light of observational evidence for trends in temperature, rainfall, river flow and aquifer recharge patterns

Hydrological outlook UK - May 2020

The Hydrological Outlook provides an insight into future hydrological conditions across the UK. Specifically, it describes likely trajectories for river flows and groundwater levels on a monthly basis, with a particular focus on the next three months. Well established monitoring programmes provide the current status of both river flows and groundwater levels at many sites across the UK, and data from these programmes provide the starting point for the Outlook. A number of techniques are used to project forwards from the current state and results from these are used to produce a summary that includes a highlights map

Hydrological outlook UK - October 2020

The Hydrological Outlook provides an insight into future hydrological conditions across the UK. Specifically, it describes likely trajectories for river flows and groundwater levels on a monthly basis, with a particular focus on the next three months. Well established monitoring programmes provide the current status of both river flows and groundwater levels at many sites across the UK, and data from these programmes provide the starting point for the Outlook. A number of techniques are used to project forwards from the current state and results from these are used to produce a summary that includes a highlights map

Hydrological summary for the United Kingdom: August 2013

The monthly summary of hydrological conditions in the United Kingdom is compiled as part of the National Hydrological Monitoring Programme (a joint CEH and BGS enterprise). The report features contemporary data for rainfall, river flow, reservoir and groundwater levels in the form of maps and graphs. A commentary is provided on the status of the nation’s water resources and any notable hydrological events during the month. The National River Flow and National Groundwater Level Archives help provide an historical context for these contemporary assessments. Financial support for the production of the Hydrological Summaries is provided by Defra, the Environment Agency, the Scottish Environment Protection Agency, the Rivers Agency in Northern Ireland and the Office of Water Services

UK hydrological review 2007

This hydrological review, which also provides an overview of water resources status throughout 2007, was undertaken as part of the National Hydrological Monitoring Programme (NHMP). The NHMP was set up in 1988 to document hydrological and water resources variability across the UK. It is a collaborative programme between the Centre for Ecology & Hydrology, which maintains the National River Flow Archive and the British Geological Survey which maintains the National Groundwater Level Archive. Both organisations are component bodies of the Natural Environment Research Council. This report has been compiled with the active cooperation of the principal measuring authorities in the UK: the Environment Agencya, the Scottish Environment Protection Agency and, in the Northern Ireland, the Rivers Agency. These organisations provided the great majority of the required river and groundwater level data. The Met Office provided almost all of the rainfall and climatological information featured in the report and the reservoir stocks information derive from the Water Service Companies, Scottish Water and Northern Ireland Water. Groundwater level data for Northern Ireland was provided by the Northern Ireland Environment Agency. The provision of the basic data, which provides the foundation both of this report and the wider activities of the NHMP, is gratefully acknowledged. A primary source of information for this review is the series of monthly UK Hydrological Summaries (for further details please visit: http://www.ceh.ac.uk/data/nrfa/water_watch.html. Financial support for the production of the Hydrological Summaries is provided by the Environment Agency, the Scottish Environment Protection Agency, the Rivers Agency (Northern Ireland) and the Office of Water Services (OFWAT)

Human influences on streamflow drought characteristics in England and Wales

Human influences can affect streamflow drought characteristics and propagation. The question is where, when and why? To answer these questions, the impact of different human influences on streamflow droughts were assessed in England and Wales, across a broad range of climate and catchments conditions. We used a dataset consisting of catchments with near-natural flow as well as catchments for which different human influences have been indicated in the metadata (Factors Affecting Runoff) of the UK National River Flow Archive (NRFA). A screening approach was applied on the streamflow records to identify human-influenced records with drought characteristics that deviated from those found for catchments with near-natural flow. Three different deviations were considered, specifically deviations in (1) the relationship between streamflow drought duration and the base flow index, BFI (specifically, BFIHOST, the BFI predicted from the hydrological properties of soils), (2) the correlation between streamflow and precipitation and (3) the temporal occurrence of streamflow droughts compared to precipitation droughts, i.e. an increase or decrease in streamflow drought months relative to precipitation drought months over the period of record. The identified deviations were then related to the indicated human influences. Results showed that the majority of catchments for which human influences were indicated did not show streamflow drought characteristics that deviated from those expected under near-natural conditions. For the catchments that did show deviating streamflow drought characteristics, prolonged streamflow drought durations were found in some of the catchments affected by groundwater abstractions. Weaker correlations between streamflow and precipitation were found for some of the catchments with reservoirs, water transfers or groundwater augmentation schemes. An increase in streamflow drought occurrence towards the end of their records was found for some of the catchments affected by groundwater abstractions and a decrease in streamflow drought occurrence for some of the catchments with either reservoirs or groundwater abstractions. In conclusion, the proposed screening approaches were sometimes successful in identifying streamflow records with deviating drought characteristics that are likely related to different human influences. However, a quantitative attribution of the impact of human influences on streamflow drought characteristics requires more detailed case-by-case information about the type and degree of all different human influences. Given that, in many countries, such information is often not readily accessible, the approaches adopted here could provide useful in targeting future efforts. In England and Wales specifically, the catchments with deviating streamflow drought characteristics identified in this study could serve as the starting point of detailed case study research