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A modelling study was undertaken to quantify effects that the climate likely to prevail in the 2050s might have on water quality in two contrasting UK rivers. In so doing, it pinpointed the extent to which time series of climate model output, for some variables derived following bias correction, are fit for purpose when used as a basis for projecting future water quality. Working at daily time step, the method involved linking regional climate model (HadRM3-PPE) projections, Future Flows Hydrology (rainfall–runoff modelling) and the QUESTOR river network water quality model. In the River Thames, the number of days when temperature, dissolved oxygen, biochemical oxygen demand and phytoplankton exceeded undesirable values (>25°C, <6 mg L−1, >4 mg L−1and >0.03 mg L−1, respectively) was estimated to increase by 4.1–26.7 days per year. The changes do not reflect impacts of any possible change in land use or land management. In the River Ure, smaller increases in occurrence of undesirable water quality are likely to occur in the future (by 1.0–11.5 days per year) and some scenarios suggested no change. Results from 11 scenarios of the hydroclimatic inputs revealed considerable uncertainty around the levels of change, which prompted analysis of the sensitivity of the QUESTOR model to simulations of current climate and hydrology. Hydrological model errors were deemed of less significance than those associated with the derivation and downscaling of driving climatic variables (rainfall, air temperature and solar radiation). Errors associated with incomplete understanding of river water quality interactions with the aquatic ecosystem were found likely to be more substantial than those associated with hydrology, but less than those related to climate model inputs. These errors are largely a manifestation of uncertainty concerning the extent to which phytoplankton biomass is controlled by invertebrate grazers, particularly in mid-summer; and the degree to which this varies from year to year. The quality of data from climate models for generating flows and defining driving variables at the extremes of their distributions has been highlighted as the major source of uncertainty in water quality model outputs.EDITOR A. Castellarin; ASSOCIATE EDITOR X. Fang [ABSTRACT FROM AUTHOR]

Anthropogenic changes to the temperature regimes of rivers, whether through thermal pollution, removal of shade, or climate change, could affect community stability and cause phenological changes in aquatic species. This study examines the impact of a thermal discharge from a power station on the diversity and composition of the aquatic macroinvertebrate community in the River Severn, UK. Daily temperatures up to 2 km downstream of the thermal discharge averaged 4.5°C above ambient. Abundance and taxon richness metrics were reduced at a site approximately 0.5 km downstream of the power station outfall, but were largely unaffected at a second site about 2 km downstream. The majority of the macroinvertebrate taxa observed were recorded at both control and heated sites, suggesting species were below their thermal tolerance threshold or had developed adaptations to survive increased temperatures. However, indicator species analysis suggests certain taxa were associated with particular sites; abundances of Musculium lacustre, Simulium reptans, and Orthocladiinae were greater at the unheated control site, whereas more pollution-tolerant species such Asellus aquaticus and Erpobdella octoculata were more common in the thermally impacted reaches. Overall, the results provide an indication of potential species and community response to future warming under climate change scenarios. [ABSTRACT FROM AUTHOR]

Change in river water temperature has important consequences for the environment and people. This review provides a new perspective on the topic by evaluating changes in river water temperature for the UK over the 20th century and possible changes over the 21st century. There is limited knowledge of space-time variability in, and controls on, river temperature at the region scale and beyond over the 20th century. There is historical evidence that UK river temperature has increased in the latter part of the 20th century, but low agreement on the attribution of changes to climatic warming because river temperature is a complex, dynamic response to climate and hydrological patterns moderated by basin properties and anthropogenic impacts. Literature is scarce to evaluate changes to UK river temperature in the 21st century, but it appears as likely as not that UK river temperature will increase in the future. However, there are a number of interlinked sources of uncertainty (related to observations, scenarios, process interactions and feedback) that make estimating direction and rate of temperature change for rivers across the UK with confidence very challenging. Priority knowledge gaps are identified that must be addressed to improve understanding of past, contemporary and future river temperature change. [ABSTRACT FROM AUTHOR]

Macroinvertebrate communities in Western European rivers have changed substantially in recent decades. Understanding the causes is challenging because improvements in water quality have coincided with climatic variations over this period. Using data covering >2300 rivers and 21 years (1991-2011) across England and Wales, we analysed family-level distributions and nationwide trends in prevalence (proportion of sampling locations where an organism was present) to diagnose the causes of ecological change. Our aims were to: (i) reveal the taxa driving assemblage-level trends; (ii) identify the main changes in family-level prevalence and distribution patterns; and (iii) test whether changes were accounted for by improving water quality, increasing temperatures or variations in discharge. While previous analyses revealed increasing richness among British river invertebrates, a partial turnover of taxa is now evident. Two distinct components of temporal trend have comprised: (i) overall increases or decreases in taxon prevalence over 21 years, which correlated with pollution sensitivity and discharge; and (ii) short-term variations in prevalence that correlated primarily with temperature and nutrient concentrations. The longer-term changes in prevalence were reflected in expansions or contractions in families' distributions linked to water quality, with little evidence of shifts consistent with increasing temperatures. Although these monitoring data had limitations (e.g., family-level data, few headwaters), they provide no clear evidence of long-term climate effects on invertebrates; the one feature consistent with climate warming - a small northward expansion of the range of many taxa - was accounted for by large improvements in water quality in northern England. Nevertheless, changes linked to discharge and temperature over the shorter-term (<2 years) point to the climatic sensitivity of invertebrate communities. It is therefore likely that any long-term climatic changes since 1990 have been outweighed by the strength and geographical extent of the recovery from poor water quality. [ABSTRACT FROM AUTHOR]

Highlights: [•] We assess the effects of climate policy on catchment-scale hydrological impacts. [•] The effects of policy are small to at least 2030. [•] By 2080 effects are small relative to the range in impact between climate models. [•] Policy however delays by several decades impacts that would have occurred in 2050. [•] We use six UK catchments to illustrate the effects of climate policy. [ABSTRACT FROM AUTHOR]

I have used the Lempel–Ziv measure to assess the complexity in riverflow activity over England and Wales for the period 1867–2002. In particular, I have examined the reconstructed monthly riverflow time series from fifteen representative catchments in these regions and calculated the Lempel–Ziv Complexity (LZC) value for each time series. The results indicate that the LZC values in some catchments are close to each other while in others they differ significantly. In addition, I have divided the period 1867–2002 into four equal subintervals: (a) 1867–1900, (b) 1901–1934, (c) 1935–1968, (d) 1969–2002, and calculated the LZC values for the various time series in these subintervals. It is found that during the period 1969–2002, there is a decrease in complexity in most of the catchments in comparison to the subinterval 1935–1968. This complexity loss may be attributed to increased human intervention involving land and crop use, urbanization, commercial navigation and climatic changes due to human activity. Determining the complexity in the riverflow time series is important because an understanding of the extent of complexity may be useful in developing appropriate models of riverflow activity. The extent of complexity may also influence the predictability of the variability in riverflow dynamics. [ABSTRACT FROM AUTHOR]

A modelling study has been undertaken to assess the likely impacts of climate change on water quality across the UK. A range of climate change scenarios have been used to generate future precipitation, evaporation and temperature time series at a range of catchments across the UK. These time series have then been used to drive the Integrated Catchment (INCA) suite of flow, water quality and ecological models to simulate flow, nitrate, ammonia, total and soluble reactive phosphorus, sediments, macrophytes and epiphytes in the Rivers Tamar, Lugg, Tame, Kennet, Tweed and Lambourn. A wide range of responses have been obtained with impacts varying depending on river character, catchment location, flow regime, type of scenario and the time into the future. Essentially upland reaches of river will respond differently to lowland reaches of river, and the responses will vary depending on the water quality parameter of interest. [ABSTRACT FROM AUTHOR]

Several studies have highlighted an increase in DOC concentration in streams and lakes of UK upland catchments though the causal mechanisms controlling the increase have yet to be fully explained. This study, compiles a comprehensive data set of DOC concentration records for UK catchments to evaluate trends and test whether observed increases are ubiquitous over time and space. The study analysed monthly DOC time series from 198 sites, including 29 lakes, 8 water supply reservoirs and 161 rivers. The records vary in length from 8 to 42 years going back as far as 1961. Of the 198 sites, 153 (77%) show an upward trend in DOC concentration significant at the 95% level, the remaining 45 (23%) show no significant trend and no sites show a significant decrease in DOC concentration. The average annual increase in DOC concentration was 0.17 mg C/l/year. The dataset shows: (i) a spatial consistent upward trend in the DOC concentration independent of regional effects of rainfall, acid and nitrogen deposition, and local effects of land-use change; (ii) a temporally consistent increase in DOC concentration for period back as far as the 1960s; (iii) the increase in DOC concentration means an estimated DOC flux from the UK as 0.86 Mt C for the year 2002 and is increasing at 0.02 Mt C/year. Possible reasons for the increasing DOC concentration are discussed. [ABSTRACT FROM AUTHOR]

Discusses the effects of climate change scenarios in the increase in frequency and magnitude of flooding events in rivers in Britain. Rainfall-runoff model; Climate change; Effect of changes in rainfall patterns; Land use change.

The hydrodynamic characteristics of in-stream vegetation can significantly alter river flowconveyance, notably through a reduction in local velocity and increases in flow depth, whichhas implications for nature-based flood mitigation. Research suggests a warmer climate willalter the growth cycle of vegetation, extending periods of high growth to coincide withperiods of increased precipitation, increasing fluvial flood risk as precipitation eventsincrease in intensity and frequency under climate change. Hydraulic modellingcan complement management strategies by capturing complex flow-vegetationinteractions for hypothetical climate scenarios to enhance the understanding of theimpact vegetation and climate change has on flood risk. However the impact ofprecipitation events on vegetated rivers and the influence climate change will haveon the resulting flood risk is yet to be addressed using 3D numerical modellingtechniques. Telemac 3D is an open-source solver suite capable of simulating open-channel freesurface flow at reach scales. This study used Telemac 3D to study seasonal vegetationchanges on flow for a single reach of the River Blackwater, UK, to assess the accuracy towhich vegetation-flow interactions were represented. Calibration consisted of modifying avegetation bulk drag coefficient until best-fit between measured and simulated flow quantitieswas achieved. Flow scenarios were based on the climate model ensembles provided byavailable hydrological model datasets using the RCP8.5 emission scenario in the literature.The results indicate that the model accurately predicts changes to complex open-channelflow and is representative of observed vegetation-flow dynamics, such as the localreduction in the 3D velocity field. This work has potentials for flood mitigationstrategies utilising nature-based approaches: informing the management of flood-pronereaches or the selective use of in-stream vegetation to promote flood detention. [ABSTRACT FROM AUTHOR]