232 research outputs found
Climate-driven changes in UK river flows: a review of the evidence
Get PDFThere 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
Get PDFThe 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
Get PDFComplete 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
Get PDFThe 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
Get PDFAcross 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
Get PDFThe 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
Get PDFThe 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
Get PDFThe 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
The Spatial Coherence of European Droughts – Final Report
Get PDFDrought can cause serious problems across much of Europe. Many droughts are localised and short, but others are widespread and cause environmental and social effects that cross international boundaries. Some of the most important UK droughts were also significant droughts across much of Europe. Intuitively, it would seem that there may be considerable potential for developing improved drought monitoring and forecasting tools by examining the spatial coherence of droughts on a continental scale.
This project has considered the potential for developing new approaches to forecasting drought by asking the following research questions:
• Is there any systematic time lag between the onset and development of droughts in different parts of Europe?
• Can the onset and development of droughts in some parts of Europe provide an early warning for the development of droughts in other parts of Europe, and in particular, in the UK?
• Can these relationships be used to build reliable and robust operational tools for UK drought forecasting?
The method, which draws on a unique archive of flow and rainfall data from across much of Europe, involved the following steps.
1. Calculate a normalised deficiency index for each site – a measure of drought that allows comparison between locations with different climatological and hydrological regimes, and between different seasons
2. Group catchments with similar drought characteristics into regions
3. Develop standardised flow and rainfall deficiency indices for these regions
4. Analyse relationships between regions and develop statistical models to predict drought.
Twenty-four homogenous regions were identified across Europe; catchments within these groups frequently experience simultaneous streamflow deficiencies. Four distinct geographical regions emerged in the UK. A further group, comprising very slow-responding catchments (Base Flow Index > 0.8), was identified in southeast England.
For each of these regions, time series of regional streamflow and rainfall deficits were defined and a catalogue of regional drought severity developed, spanning 1901 – 2005 for meteorological droughts, and 1961 – 2005 for hydrological droughts. This enabled a characterisation of major drought periods, in terms of duration, seasonality and spatial coherence in the various regions. This drought catalogue is a major deliverable of this project, and will be of considerable practical utility for drought management and future research in the UK and in Europe.
For major post-1961 streamflow droughts, a comprehensive description of the extent and spatio-temporal development of the drought was provided. A standalone publication has been produced, which illustrates the evolution of streamflow and rainfall anomalies, along with climatic drivers and large-scale atmospheric circulation anomalies for major droughts (e.g. 1975 – 76; 1988 – 1992). From an appraisal of these events, it is clear that most droughts appear to have different characteristics, in terms of their duration, spatial coherence and seasonality. For example, a contrast was found between the 1976 drought, which was spatially consistent across much of Europe and was combined with a rainfall deficiency the preceding winter and a heat wave in the summer, and the 1995-1997 drought, which was interspersed by wet episodes and had little long-lasting spatial coherence over Europe. In most historical events, the UK experienced drought simultaneously with other European regions, or earlier; there was little evidence of any systematic lag time which could be readily exploited in the development of early warning systems for the UK based on conditions in other parts of Europe.
An exploratory data analysis was then carried out, to determine whether there are relationships in the drought indicators which could be exploited to develop forecasting tools. Correlation analysis, multidimensional scaling and statistical modelling were applied to find relationships, which were generally fairly weak. Low correlations exist between regional drought deficiency time series of different regions, and the correlation patterns for hydrological and meteorological droughts are similar, albeit slightly higher for the latter. Correlations with the rest of Europe are stronger in winter than in summer for northern and western Britain, but are of similar magnitude all year round for southeast England. Although a relationship was identified between the length of a UK drought and the number of regions contemporaneously experiencing drought elsewhere in Europe, it was found that this relationship was not statistically significant.
Following these exploratory analyses, statistical models were built for each UK region, which predict the number of drought months that may occur in the next 6 months. Predictions are based on streamflow deficiencies in other European regions, so the models essentially predict ‘drought from drought’ – i.e. they use the spatial coherence of anomalies to derive forecasts for the UK based on deficiencies on the continent. The models forecast droughts in groundwater-dominated catchments in southeast England reasonably well. In northwest Britain, however, the predictive capability is poor.
Importantly, the models have some significant benefits when compared to previous seasonal forecasting studies – in particular, the approach is based on large regions, rather than being ‘tuned’ to particular catchments, and they enable forecasting of winter anomalies rather than just summer flows. Furthermore, the models perform reasonably well at forecasting the cessation of drought conditions. These attributes mean that the models could potentially be of high utility during long, multi-season drought events, to determine whether a drought is likely to intensify or to diminish. Whilst the predictive capacity is modest in some regions, the models clearly have potential for application in UK drought management, although there are also important practical considerations – in particular, the need for timely data supply from across Europe – which would need to be examined in further research before they could evolve into an operational tool.
Further analysis concentrated on attempting to explain observed patterns of spatial coherence, by linking drought indicators to large scale modes of atmospheric variability (e.g. the North Atlantic Oscillation and the East Atlantic-West Russia pattern). In some regions and some seasons, these predictors clearly play an important role in determining the spatial coherence of droughts. Whilst their predictive capability is relatively weak at present, there is undoubtedly scope for refining these relationships into tools for monitoring and providing indicative forecasts. An advantage of this approach is that some climatological indicators are routinely forecast (although the modest skill levels are a further obstacle to application at present).
The regional drought indicators are shown to be powerful tools for illustrating the dynamics of rainfall and streamflow deficiencies. They could therefore find application in UK and European drought monitoring systems. Again, there would be important practical limitations to consider, and further research would be needed to optimise the indicators for use in monitoring. However, they could potentially fill an important gap; existing monitoring European drought monitoring systems lack a streamflow component, whilst UK approaches (e.g. CEH’s monthly Hydrological Summaries) consider runoff deficiencies but do not use any metrics tailored specifically to drought
UK hydrological review 2007
Get PDFThis 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)
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