Climate change and water in the UK: Recent scientific evidence for past and future change

Abstract

A changing climate is anticipated to alter hydroclimatological and hydroecological processes across the UK and around the world. This paper builds on a series of reports commissioned in 2012 (Water Climate Change Impacts Report Card [WCCRC], 2012) and published in a special issue of Progress in Physical Geography in 2015 that interpreted and synthesised the relevant, peer-reviewed scientific literature of climate change impacts on the UK’s water environment. It aims to provide reliable, clear information about the potential impacts of climate change on hydrology and the water environment. We review new evidence since 2012 for historical and potential future changes in precipitation and evapotranspiration, river flows and groundwater levels, river and groundwater temperature/quality and, finally, aquatic ecosystems. Some new evidence exists for change in most of these hydrological components, typically in support of the spatial and temporal trends reported in WCCRC 2012. However, it remains the case that more research has been conducted on rainfall and river flows than evapotranspiration, groundwater levels, river and groundwater temperature, water quality or freshwater ecosystems. Consequently, there remains a clear disparity of robust evidence for historical and potential future change between the top and bottom of the hydroclimatological–hydroecological process chain. As was the case in WCCRC 2012, this remains a significant barrier to informed climate change adaptation in these components of the water environment.

Keywords

Climate change climate change impacts water water environment hydrology hydroclimatology hydroecology adaptation

I Introduction

The availability of reliable, clear information about the potential impacts of climate change on hydrology and the water environment remains a barrier to climate change adaptation in the UK, and worldwide (Watts et al., 2015a). To address this stumbling block, a series of reports was commissioned in 2012 (Watts and Anderson, 2013; Water Climate Change Impacts Report Card; referred to as WCCRC 2012 herein) that interpreted and synthesised peer-reviewed scientific literature detailing the impacts of climate change on the UK’s water environment. These reports were subsequently published in a 2015 special issue of Progress in Physical Geography. This paper aims to update the findings of those reports by reviewing new literature published since 2012. Specific objectives are as follows: (1) to synthesise the evidence of historical changes to UK hydrology and the water environment; (2) to summarise projected changes for the 21st century; and (3) to identify the outstanding research needs to improve understanding of the water-related impacts of climate change.

As in WCCRC 2012, we review the evidence for changes along the hydroclimatological process chain and into the hydroecological process chain. Specifically, we review new evidence for historical and potential future changes in precipitation and evapotranspiration, followed by river flows and groundwater levels, and then river and groundwater temperature/quality. Finally, we review new evidence for change in aquatic ecosystems. The paper is focused primarily on observed and projected change in components of the water environment that are modified by anthropogenic climate change. There are multiple, often interlinked, confounding factors that may have influenced any detected changes; therefore, unless all other possible causes can be excluded then changes are not, and indeed should not be, attributed to human-modified climate change.

II Historical changes

In this section, scientific evidence of historical changes to the UK water cycle published since 2012 is reviewed.

1 Precipitation and evapotranspiration

WCCRC 2012 reported small but significant increases in winter rainfall intensity and duration, and also increases in intensity of long-duration summer rainfall. However, there was no evidence to suggest that these trends were driven by anthropogenic climate change (Watts et al., 2015b). Since 2012, studies have focused on specific regions (e.g. Afzal et al., 2015; Kosanic et al., 2014) and used new datasets (Kosanic et al., 2014; Simpson and Jones, 2014) and/or methods (e.g. Jones et al., 2014; Prosdocimi et al., 2014) to analyse historical change at annual and seasonal timescales.

At the annual timescale, significant positive trends have been detected in rainfall totals within Scotland (Afzal et al., 2015, period 1961–2000) and also in the magnitude of extreme rainfall events (i.e. maxima) in the north (especially Scotland; e.g. Prosdocimi et al., 2014, period 1961–2010; Jones et al., 2014, period 1961–2010) and west (Jones et al., 2014) of the UK. Significant decreases are observed in the magnitude (Jones et al., 2014) and intensity (Kosanic et al., 2014, period 1975–2010) of extreme precipitation events in southern regions. However, no significant positive or negative trend is observed in annual extreme events across the majority of the UK (Prosdocimi et al., 2014).

Seasonally, average rainfall and rainfall intensity have increased significantly in winter months (December, January and February) throughout the UK, with the greatest changes observed in Scotland (Simpson and Jones, 2014, period 1932–2010; Wilby and Quinn, 2013, period 1871–2011). Winter rainfall maxima have increased in the north of England and Scotland, and summer maxima have decreased in the south of England (Prosdocimi et al., 2014). Afzal et al. (2015), Kosanic et al. (2014) and Simpson and Jones (2014) propose that the trends they detected may be linked to natural periodicities associated with the North Atlantic Oscillation (NAO). The NAO may have been enhanced by a changed climate (Simpson and Jones, 2014). However, this hypothesis has not been tested systematically. There remains insufficient evidence to propose a link between anthropogenic climate change and these reported changes in precipitation. This is unsurprising, since it has been suggested that a link may not become evident until the 2050s (Fowler and Wilby, 2010).

WCCRC 2012 reported only one study (for a single site) of historical changes in evapotranspiration (evaporation to the atmosphere from soil and water surfaces, and vegetation; Kay et al., 2013) in the UK, which demonstrated an increase in potential evapotranspiration (PE, the amount of moisture lost to atmosphere if there are no limits on water supply; Federer et al., 1996) and a decrease in actual evapotranspiration (AE, loss of moisture limited by soil wetness; Kay et al., 2013). In 2012 there was no evidence to suggest a link between anthropogenic climate change and changes in evapotranspiration. There remains no published study with national coverage of historical changes (Kay et al., 2013). However, Clark (2013) reports on changes in AE and PE at a site in the upper Brue catchment, Somerset. No consistent trend was observed in PE over the period 1986–2010; PE increased by ∼50 mm between 1986 and 1996 but declined thereafter, by ∼30 mm. AE decreased by ∼15% between 1996 and 2008, which is consistent with observations made using the global FLUXNET dataset (see Jung et al., 2010). Consequently, the decrease in AE may be representative of a wider area (Clark, 2013), although this hypothesis was not tested. Changes in AE and PE were significantly correlated with air temperature and precipitation respectively, but not linked to anthropogenic climate change.

2 River flows and groundwater levels

WCCRC 2012 synthesised numerous spatially and temporally extensive studies of large-scale changes in river flow throughout the UK. There have been no further studies of change in annual, seasonal or monthly average river flow regimes or low flows/droughts. However, recent studies have employed new statistical methods (e.g. Prosdocimi et al., 2014) and used long-term qualitative datasets (e.g. Stevens et al., 2014) to provide further evidence of variability in high river flows and floods. The findings of Prosdocimi et al. (2014) agree broadly with evidence first presented by Hannaford and Marsh (2008) of increased annual flow maxima in northern England, northern Scotland and south Wales, and increased winter maxima in north-west England. At the time of WCCRC 2012, no study had documented a clear pattern of change in summer flows. However, Prosdocimi et al. (2014) observed downward trends in south and south-east England and upward trends in Northern Ireland, north and west Great Britain. There remains (after Watts et al., 2015b) little compelling evidence for any long-term increase in flood frequency. Muchan et al. (2015) suggest that flood magnitude (defined as the October–September water year maximum flow) decreased in the River Thames between the 1880s and 2014. However, evidence for a trend could have been influenced by: (1) a decline in snowmelt contributions to major floods (Marsh and Harvey, 2012), since some of the biggest floods were driven by snowmelt; and (2) the occurrence of ‘flood-rich’ and ‘flood-poor’ periods throughout the record (Wilby and Quinn, 2013). Stevens et al. (2014) observed an increase in reported flood events during the late 20th and 21st century and significant inter-decadal variation in flood-rich and flood-poor periods. However, no long-term trend was evident once the datasets were normalised by population size and number of dwellings (to account for bias in a dataset that relied on public reports of flooding; Stevens et al., 2014).

No studies of historical changes in groundwater level within the UK existed in 2012; consequently, no links with anthropogenic climate change could be made. However, since WCCRC 2012, a new study has revealed historical variability in UK groundwater levels. Groundwater level data from seven boreholes located on the Chalk aquifer were analysed by Jackson et al. (2015). Each record was >40 years long and part of the UK’s long-term observation borehole network. Groundwater levels declined significantly at four sites, including the two with the longest records. Climate change was postulated as a driver for the observed declines, but trends could not be attributed definitively to anthropogenic climate modifications (Jackson et al., 2015). Indeed, Lavers et al. (2015) demonstrate that groundwater levels are linked strongly to meteorological variability (i.e. sequences of atmospheric patterns, water vapour transport and, in turn, precipitation). Furthermore, Jackson et al. (2015) state that the groundwater systems they studied could have been influenced by changes in abstraction and/or resource management practices.

To summarise, there remains little evidence of change in groundwater levels and low flows across the UK. However, studies published since 2012 broadly corroborate evidence of change presented in WCCRC 2012 (i.e. increase in high flows, particularly in the north and west, but no evidence of change in flood frequency). Furthermore, previously undetected changes in summer maxima demonstrate increases in Northern Ireland, the north and west of the UK, but decreases in south and south-east England. However, none of the observed changes have been attributed to anthropogenic climate change.

3 River and groundwater temperature and quality

There remains (after Watts et al., 2015b) scarce information on historical changes in groundwater temperature in the UK and no investigation of links to anthropogenic climate change; no new studies have been published since 2012. Studies of historical changes in river water temperature are also scarce, but generally report increases (Hannah and Garner, 2015; Watts et al., 2015b). Orr et al. (2015) applied sophisticated trend-detection methods to a subset (2773 sites) of the dataset used by Des Clers et al. (2008; as described in WCCRC 2012) to identify temperature increases at 86% of locations; a mean annual increase in water temperature of 0.03°C year^-1 was observed for the period 1990–2006. This change is similar to increases in air temperature over the same period (as reported by Jenkins et al., 2008) and was inferred to be driven (in the absence of other systematic influences) by anthropogenic climate change. Garner et al. (2014a) analysed the same dataset but observed no trend in the frequency of occurrence of shape (timing of features) or magnitude (size) of annual river temperature regime classes for the period 1989–2006.

WCCRC 2012 documented changes in river water quality and suggested that they were driven predominantly by changes in land-use (e.g. Battarbee et al., 2014; Malcolm et al., 2014; Montieth et al., 2014), land-management (e.g. Battarbee et al., 2014) and pollution (e.g. Curtis et al., 2014; Howden et al., 2010; Watts et al., 2015b). However, there remains no evidence to suggest a link between anthropogenic climate change and historical changes in river water quality (after Watts et al., 2015b). There remain (after Watts et al., 2015b) no studies that link historical change in groundwater quality to anthropogenic climate change. Studies published since 2012 have considered industrial (e.g. Rivett et al., 2012) and agricultural sources of pollution (Zhang et al., 2013), but not anthropogenic climate change.

4 Freshwater ecosystems

WCCRC 2012 reported that freshwater ecosystems should be considered to be among the most sensitive to anthropogenic climate change (after Durance and Ormerod, 2007, 2009) because they are influenced by many interacting factors (i.e. discharge, light, water temperature, nutrient availability, habitat connectivity, species interactions and land and water management practices; Laize et al., 2014). However, due to a lack of long-term, systematic records there were only a few, geographically isolated studies that supported this statement (i.e. Clews et al., 2010; Durance and Ormerod, 2007, 2010). Since 2012, Vaughan and Ormerod (2014) used data collected in 21 sampling years (1991–2011) from >2300 rivers across England and Wales to detect evidence of climate-induced changes in the spatial distribution of freshwater invertebrate taxa, but identified no clear evidence of a climate change influence. Instead, the only observation consistent with climate warming (i.e. a northward expansion of the range of many taxa) was accounted for by water quality improvements in northern England. However, taxa were extremely sensitive to shorter-term (<2 years) inter-annual variation in temperature and discharge. Therefore, some of the long-term changes observed may have been driven by a changing climate, but these were not as influential as changes in the magnitude and geographical extent of water quality improvements (Vaughan and Ormerod, 2014). There remains little historical evidence to suggest that freshwater ecosystems have responded to anthropogenic climate change. An environment of improved water quality should allow ecological responses to climate-induced drivers (such as discharge and temperature) to be more easily identified (Durance and Ormerod, 2009) as long as long-term, systematic data collection continues.

5 Summary of historical changes and links to anthropogenic climate change

Changes have been detected in most parts of the UK water environment during the last century, although groundwater quality is a notable exception. As was the case in 2012, there has been no robust, formal attribution of observed changes in any component of the UK water environment to anthropogenic climate change. Nonetheless, there is further systematic, spatially and temporally comprehensive evidence for change, especially in precipitation and river flows. Less evidence is available for evapotranspiration, groundwater levels, river and groundwater quality (including water temperature) and freshwater ecosystems. Confidence assessments (see Fung et al., 2015; Watts and Anderson, 2013) for the level of agreement for evidence of historical changes and the robustness of that evidence for each reviewed component of the UK water environment are provided in Table 1.

Table 1.

Confidence assessment for observed historical changes in components of the UK water environment during the 20th century. Each component is awarded a score of high (H), medium (M) or low (L). Scores address evidence for change but not whether this was driven by anthropogenic climate change.

Component of water environment	Level of agreement	Amount of evidence (type, amount, quality, consistency)
Precipitation	H	M
Evapotranspiration	L	L
River flows	L	M
Groundwater recharge and levels	L	L
River water temperature	M	M
River water quality and ecology	L	L
Groundwater temperature and quality	L	L

III Potential future changes

This section considers the impact of projected climate changes on the UK freshwater environment over the 21st century. Most of the studies presented used a simulation model-based framework to make projections. The dynamics of future climate must be anticipated before these data can be used to project future hydrological trends. Within this framework, general circulation models (GCMs, often using an ensemble approach to represent climate model uncertainty) are used to simulate global climate processes and account for anthropogenically driven increases in greenhouse gas concentrations (see Prudhomme et al., 2003). Because GCMs model climate at coarse resolution (50–100 km; Maraun et al., 2010), outputs are often downscaled to smaller spatial domains (12–50 km; Maraun et al., 2010) using regional climate models (RCMs) or statistical methods (see Prudhomme et al., 2003; Wilby et al., 1998; Wood et al., 2004). In turn, these climate data are then used to drive process-based models of projected changes in the water environment (sometimes using multiple models to account for uncertainties in hydrological and associated model structure).

1 Rainfall and evapotranspiration

WCCRC 2012 reported on projected changes to annual and seasonal precipitation across the UK. Projections of extreme precipitation during spring, summer and autumn were also documented, but at the time of the report, climate models were deemed unreliable for representing heavy and short-duration events (Fowler et al., 2007) that occur often in the UK during summer months. Recently, the first long-term (20-year) simulations were performed with a ‘convection-permitting’ model (as used for short-range weather forecasting) that operates on a very fine resolution grid (1.5 km), permitting a more realistic representation of convection over the UK and, thus, hourly rainfall characteristics, including extremes (Kendon et al., 2012, 2014). When driven by a single climate model and run for the southern UK, the convection-permitting model indicated that the intensity of short-duration rainfall will increase by around 10% across a range of return periods during summer months (June, July and August), but that dry spells will become longer (Chan et al., 2014; Kendon et al., 2014). Winter precipitation (December, January and February) was also projected to intensify by ≥40% across a range of return periods. Although the convection-permitting model incorporates improved process representation, it is computationally intensive to run (Kendon et al., 2014). Consequently, model results to date are based on one climate model (i.e. Met Office Unified Model) and one emissions scenario (i.e. Intergovernmental Panel on Climate Change [IPCC] Representative Concentration Pathway [RCP] 8.5, highest greenhouse gas emissions; Riahi et al., 2011). Uncertainty arising from model structure and emissions scenario has, therefore, not been assessed (Kendon et al., 2014).

Projections of PE are highly dependent on the method of calculation used (Prudhomme and Williamson, 2013), as demonstrated by Sheffield et al. (2012) and Dai (2013). Furthermore, they are also confounded by poor understanding of possible changes in plant transpiration and growth (Kay et al., 2013; Van den Hoof et al., 2013). Most projections indicate annual PE increases, but some suggest decreases for some months (Kay et al., 2013; Prudhomme and Williamson, 2013). Prudhomme and Williamson (2013) projected percentage changes in PE using 12 equations of varying complexity driven by the Hadley Centre’s HadRM3-Q0 model outputs representative of 1961–1990 (with MORECS PE (see Hough and Jones, 1997) used as reference PE) and 2041–2070. In broad agreement with the studies reported in WCCRC 2012, Prudhomme and Williamson (2013) project predominantly increased PE across the UK. The largest increases in PE were anticipated in north-western Great Britain in January, while the smallest were predicted to occur in July and October (in the same region). Exact magnitudes were largely dependent on the method of calculation: the Turc (Turc, 1961), Jensen–Haise (Jensen and Haise, 1963) and calibrated Blaney–Criddle (Blaney and Criddle, 1950) methods systematically projected the largest increases across Great Britain in all months, while the Priestley–Taylor (Priestley and Taylor, 1972), Makkink (Jacobs et al., 2009) and Thornthwaite (Thornthwaite, 1948) methods projected the smallest (Prudhomme and Williamson, 2013). Prudhomme and Williamson (2013) recommended the use of the FAO56 method (Allen et al., 1998), which reproduced the reference MORECS PE data with greatest accuracy (when driven by the HadRM3-Q0 climate data) and was within the range of uncertainty defined by the ensemble of 12 PE equations.

2 River flows and groundwater levels

WCCRC 2012 reported regional and seasonal variability in projected river flows derived from various global climate models (GCMs), or ensembles thereof. The emissions scenarios, downscaling approaches, flow modelling methodologies and, thus, model uncertainties varied between studies. However, broad projections of future river flows (i.e. increased winter flows, decreased summer flows and low agreement between models on the direction of change during spring and autumn) reported in WCCRC 2012 (by Christierson et al., 2012 and Prudhomme et al., 2012) are supported by a subsequent study by Sanderson et al. (2012). In this study, runoff data from an 11-member RCM (HadRM3) ensemble (Jones et al., 1997) was driven by the Special Report on Emissions Scenarios (SRES) A1B (i.e. medium emissions) scenario (Nakićenović and Swart, 2000). However, despite broad agreement with WCCRC 2012, projected increases in winter flows are greater than decreases in summer flows, driving an overall increase in annual average river flow during the 21st century (Sanderson et al., 2012; also projected for the Eden catchment in Scotland by Ledbetter et al., 2012). This result slightly contradicts Christierson et al. (2012) and Prudhomme et al. (2012) who projected smaller increases in winter flows and, therefore, little change in annual flow regimes. Notably, Sanderson et al. (2012) used runoff data generated within an ensemble of RCMs, as opposed to using the climate data output from the RCM to drive a conventional ‘offline’ hydrological model (e.g. Christierson et al., 2012; Prudhomme et al., 2012). Furthermore, the 11-member RCM data do not sample the full range of uncertainties (Murphy et al., 2009) (unlike the UKCP09 probabilistic projections used by Christierson et al., 2012), and so the range of possible future river flows is likely greater than those projected (Sanderson et al., 2012).

WCCRC 2012 also anticipated increases in flood magnitude controlled by climate and physical characteristics of river catchments (Prudhomme et al., 2013a, 2013b). Recently, Kay et al. (2014a, 2014b) extended the work of Prudhomme et al. (2013a, 2013b; as reported in WCCRC 2012) to a larger set of catchments across Britain and projected regional impacts of climate change on 20-year flood flows during the 21st century. Projections predominantly indicate increases between the 2020s and 2080s, a result supported by Ramesan et al. (2014) who predicted similar trends in the Derwent basin, north-east England. In England and Wales, projected changes were greatest in the south east and smallest in the north east, while impacts were described as median elsewhere (Kay et al., 2014a). For Scotland, increases were greatest but more uncertain in the north and west, and lower but less uncertain in the south and east (Kay et al., 2014b). A monotonic change in flood impacts throughout Britain is not anticipated; the range of impacts within Scotland was projected to be less severe than in England and Wales (i.e. no change <–5% or >+75%; the latter is projected for the 2080s in south-eastern England; Kay et al., 2014b). Geographical variation in past river flows and, by extension, projected river flows, is controlled by variability in climate and basin processes. Charlton and Arnell (2014) applied the UKCP09 projections (for the 2020s, 2050s and 2080s) to catchment models for six catchments representing a range of hydrological conditions in England. Their results suggest that the magnitude of future high flows may be especially sensitive to basin geology; Q5 (the flow that is exceeded 5% of the time) could increase by 40%–50% in impermeable catchments compared to 20% in permeable catchments.

Drought projections reported in WCCRC 2012 were limited because studies had predominantly considered meteorological droughts (i.e. precipitation deficit; Van Loon, 2015). Prudhomme et al. (2014) investigated the effect of climate change on hydrological droughts (i.e. river flow deficit, Van Loon, 2015) in a multi-model experiment in which seven global impact models (GIMs, which represent the terrestrial water cycle at global scale and incorporate current understanding of hydrological systems) were driven by seven GCMs under four representative concentration pathways. Under RCP 8.5, Prudhomme et al. (2014) anticipate that drought frequency (proportion of time under drought conditions) and severity (defined as proportion of land under drought conditions) are very likely to increase across western Europe by the end of the 21st century. Two drivers of increased drought frequency and severity were identified: (1) the greatest increases were driven by decreased precipitation and increased evaporation; and (2) lesser increases were associated, paradoxically, with increased precipitation (up to 20%) that was offset by increased evaporation (Prudhomme et al., 2014). These projections are in agreement with Vidal and Wade (2009) and Rahiz and New (2013) but contradict Blenkinsop and Fowler (2007; all reported in WCCRC 2012); the latter suggested that the longest meteorological droughts are likely to become shorter and less severe.

WCCRC 2012 reported on a handful of studies that investigated the impact of climate change on groundwater recharge in the UK (i.e. the downward vertical flux of water to the water table; Jackson et al., 2015). Typically, reductions in annual recharge are projected (Herrera-Pantoja and Hiscock, 2008; Jackson et al., 2011; Jenkins et al., 2002). Previously unreported results of a study by Prudhomme et al. (2012) are presented by Jackson et al. (2015). Prudhomme et al. (2012) used two climate projection products: (1) the 11-member ensemble of the UK Met Office Regional Climate Model (HadRM3-PPE) as continuous time-series of climate variables from 1950 to 2099 (Prudhomme et al., 2013a); and (2) probabilistic projections of changes in climate variables as ensembles of 10,000 monthly change factors for three 30-year time-slice and greenhouse gas emission scenario combinations (i.e. 2050s and medium emissions scenario A1B; 2080s and medium emissions scenario A1B; and 2050s and high emissions scenario A1F1; see Murphy et al., 2009). These climate projections were input to a ZOOMQ3D groundwater model of the Chalk aquifer (see Jackson et al., 2011) and to R-Groundwater (Jackson, 2012) models of 24 observation boreholes in four principal aquifer types (Chalk, Limestone, Sandstone and Lower Greensand) across Great Britain. When the median values for the ensemble of 10,000 simulations are considered, annual groundwater levels are projected to decrease at 13 of 24 sites. For monthly values, the direction of change varied: (1) between sites (presumably a result of local hydrogeological conditions); and (2) between years (presumably due to interannual variability in meteorological drivers). Prudhomme et al. (2012) also reported projections forced by the A1F1 (high) emissions scenario; Jackson et al. (2015) compared these with projections forced by the A1B (medium) scenario in order to assess the sensitivity of the projected values to uncertainty in emissions scenarios. However, the impact of multiple emissions scenarios on the projections was deemed to be small in comparison to the spread of uncertainty arising from the variability in the climate ensembles. Furthermore, there is some discussion but, as yet, no quantification of potentially substantial uncertainty that may arise from the models used to represent hydrological/hydrogeological processes (Taylor et al., 2015). Jackson et al. (2015) suggest that hydrological models are used preferentially over groundwater models but that they do not represent key groundwater processes adequately (e.g. delays in the transfer of water from the soil through the unsaturated and saturated zones, to surface waters and abstraction boreholes).

3 River and groundwater temperature and quality

The published literature contains no new projections of UK river and groundwater temperature since 2012. Consequently, there remains extremely little knowledge of how these properties of the UK freshwater environment will change over the 21st century. River temperature is expected to increase (Webb and Walling, 1992), but changes to temperature regimes are likely to be moderated by river basin characteristics (e.g. water source contributions: Garner et al., 2014a; Johnson et al., 2014; basin size and orientation: Garner et al., 2014a, Hannah and Garner, 2015; density/extent of riparian shade: Garner et al., 2014b, 2015a, Johnson and Wilby, 2015).

Worldwide, there are extremely few comprehensive projections of increases in groundwater temperature. However, in one notable example for the Miramichi River system in New Brunswick, Canada, Kurylyk et al. (2014) used seven downscaled GCMs for the period 2046–2065 to drive surficial water and energy balance models and, in turn, a variably saturated groundwater flow and energy transport model; groundwater temperature was projected to increase by up to 3.6°C.

There are no new projections of UK river or groundwater quality and, as was the case in 2012, existing projections are qualitative and somewhat speculative. Potential changes in precipitation intensity, water temperature and discharge are anticipated to have consequences for UK surface water quality with increased suspended solids, sediment yields, algal growth and nutrient concentration expected (Watts et al., 2015b). Potential changes in groundwater quality may be driven by changing recharge rates plus pollutant and nutrient transport (Watts et al., 2015b).

4 Freshwater ecosystems

The impact of projected climate change on freshwater ecosystems is understudied. This is likely because water-dependent organisms are influenced by various aspects of their habitat conditions, many of which remain poorly understood and for which there exist no projections of future change (see above). In a notable exception, Fung et al. (2013) used 246 transient climate series (based on one GCM) to generate an ensemble of illustrative (given the limited number of simulations) projected river flows in the Itchen (a Chalk basin in southern England) through the 21st century. The severity and duration (in years) of low flow events within the ensembles were used to identify qualitatively (after discussion with ecologists and catchment managers) the range of possible consequences for freshwater ecosystems based on invertebrate community responses. Some 40% of models suggested that there may be significant changes to freshwater invertebrate communities in the Itchen by 2075; while the remaining 60% of models suggested that communities may recover from the short-term impacts of low flow events (Fung et al., 2013). However, the consequences of stressors such as climate change are often unpredictable on the basis of knowledge of single effects (Preston, 2002; Townsend et al., 2008); invertebrate communities are only one of many potential ecological response variables and, thus, more information on a range of structural and functional indicators is needed in order to predict ecosystem level impacts. Consequently, the anticipated effects of anthropogenic climate change on freshwater ecosystems and potential spatial variations remain highly uncertain (Watts et al., 2015b).

5 Summary of future projections

The scientific literature published since WCCRC 2012 provides further evidence that the impact of anthropogenic climate change on the UK water environment may be significant. Further evidence suggests that changes in rainfall, evapotranspiration, river flows and groundwater levels should be anticipated. The robust numerical framework within which these anticipated changes have been estimated and the consideration of multiple uncertainties provides high confidence limits to bound future projections. However, as was the case in 2012, a robust scientific evidence base to suggest future change in river and groundwater temperature, water quality and freshwater ecosystems is lacking severely and, thus, confidence in the nature of future changes is low.

Confidence assessments (see Fung et al., 2015) for the level of agreement for potential future changes and the robustness of that evidence for each reviewed component of the UK water environment are provided in Table 2. Confidence assessments for the level of agreement in future projections were provided in WCCRC 2012. We have revised the assessment for evapotranspiration, from ‘low’ (because no projections existed) to ‘medium’ following the generation of a set of projections from multiple methods and quantification of associated uncertainties.

Table 2.

Confidence assessment for projected future changes in components of the UK water environment over the 21st century. Each component is awarded a score of high (H), medium (M) or low (L).

Component of water environment	Level of agreement	Amount of evidence (type, amount, quality, consistency)
Precipitation	M	M
Evapotranspiration	M	M
River flows	L	L
Groundwater recharge and levels	L	L
River water temperature	M	M
River water quality and ecology	L	L
Groundwater temperature and quality	L	L

IV Outstanding research needs

This review aimed to update the findings of WCCRC 2012 and thus provide further reliable, clear information about the possible impacts of climate change on hydrology and the water environment in the UK. In this section, we identify the outstanding research needs to improve understanding of the water-related impacts of climate change and propose possible strategies to address remaining research gaps.

WCCRC 2012 identified several areas where research efforts should be focused: (1) evapotranspiration; (2) low flows and drought; (3) summer convective storms and consequences for future flood; (4) groundwater temperature; (5) river and groundwater temperature and quality; and (6) aquatic ecosystems. Despite growth since 2012 of the scientific literature on climate change impacts on the UK water environment, there has been little research in these areas (summer convective storms are a notable exception, although the effects of improved modelling capability in this area have not been assessed on summer floods). Instead, there has been further research on areas (i.e. precipitation and high river flows/flood) for which a (relatively) larger amount of information existed already. Consequently, more research in all of the areas identified as priorities in 2012 is still required. Furthermore, the body of evidence for historical changes and future projections shrinks (and uncertainties grow) as we move down the hydroclimatological process chain and into the hydroecological process chain (see Tables 1 and 2). This disparity means that there is an increasingly urgent need to undertake new research that contributes to the evidence base for processes at the bottom of the hydroclimatological–hydroecological process chain. Some aspects of this process chain (e.g. aquatic ecosystems) are particularly under-represented in the UK climate change evidence base, and research strategies must, therefore, be developed to address this shortcoming.

1 Why does this disparity exist?

A number of factors contribute to this disparity between historical evidence and available projections at the top versus the bottom of the hydroclimatological–hydroecological process chain. First, components of the water environment at the bottom of this process chain are influenced by multiple, interacting drivers (Heathwaite, 2010; Matthaei et al., 2010; Ormerod et al., 2010) and understanding of responses is poor. Consequently, observed patterns are confounded by shifts in other drivers of change (Darling and Côté, 2008) and in many cases there is an insufficient evidence base from which to conceptualise predictive models. Second, scientists, granting agencies and journal editors have historically favoured reductionist approaches (Jordan, 2013); that is, those based on basic relationships and processes (Sivapalan et al., 2003). However, Heathwaite (2010) suggests that reductionism is not capable of providing the concepts or methods necessary to understand the dynamics of environmental systems under a changed climate. Third, there has been, and continues to be, a lack of spatially and temporally extensive monitoring of variables and collection of metadata towards the bottom of the chain and (potentially) difficulty of access to archived data that may be held by several individuals. Therefore, there is a (perceived) lack of data from which to detect evidence of historical change and validate predictive models. Finally, where observational datasets are available, climate change projections may lie outside of the observed range (e.g. where unprecedented climate dynamics are projected, Garner et al., 2015b) and so extrapolation of these datasets is inappropriate.

2 What can be done to address this disparity and adapt despite uncertainty?

The impacts of climate change on all aspects of the UK water environment must be studied to provide robust, clear information to inform management and adaptation strategies going forward. Consequently, barriers to knowledge generation must be addressed or, where this is not possible, suitable adaptation measures must be identified in spite of uncertain projections of anticipated responses. In order to better understand complex patterns at the bottom of the hydroclimatological–hydroecological process chain (e.g. ecosystem response to climate change), a move away from reductionist research towards integrated/systems approaches is required. Water quantity, quality and freshwater ecosystems are interconnected and UK research should, therefore, integrate efforts to advance these scientific disciplines. However, this is not an easy or quick task. Lessons should, therefore, be taken from recent interdisciplinary research programs/networks that aim to integrate researchers from different scientific backgrounds in order to better understand the linkages between anthropogenic activities, water resources and aquatic ecosystems (e.g. Hering et al., 2015; Navarro-Ortega et al., 2015; Smokorowski et al., 2011). Similarly, efforts should be made to acquire the type of continuous data necessary for elucidating multi-scale complexity between hydrological processes and ecosystem responses (e.g. Fausch et al., 2002).

Where current spatio-temporal monitoring of variables is insufficient, innovative approaches combining remote sensing and modelling (e.g. Chebud et al., 2012; Vatland et al., 2015) could be applied to fill in gaps in the space or time domains. New understanding could also be generated by improving access to data held by individuals or by using space-for-time substitution methods, which use multiple sites across an environmental gradient in order to predict temporal responses in one or more physical, chemical or biological variables assumed to be driven by changes across the gradient. Lester et al. (2014) demonstrated that space-for-time substitution can generate quantitative predictions in the absence of long-term datasets or detailed mechanistic understanding of likely responses to climatic changes in distant (i.e. >2000 km apart) ecosystems. Consequently, it may be possible to transfer data and process-based knowledge from locations with similar environmental characteristics to the UK in order to predict likely responses. In this fashion, data from other locations which examine the impact of environment stressors on freshwater species similar to those present in the UK (e.g. temperature impacts on fish behaviour: Dugdale et al., 2016; water quality impacts on invertebrates: Hershkovitz et al., 2015) could be integrated with UK-centric model projections to help constrain uncertainty into the projected impacts of climate change on freshwater ecosystems. Such information could be useful in generating predictions where climate change projections lie outside of the current range of observations in the UK. Alternatively, where there is a dearth of knowledge or where knowledge is highly uncertain, adaptation should occur using ‘no or low regrets’ measures (Pittock, 2009; Wilby et al., 2010). Such measures (for example, riparian planting schemes) are anticipated to yield benefits regardless of future climate dynamics and resultant impacts on ecosystems (Clark, 2002) and can be implemented with locally available knowledge (Pittock, 2009).

Footnotes

Acknowledgements

We are grateful to Jamie Hannaford (Centre for Ecology and Hydrology) for suggestions that aided greatly in writing the section on historical changes in river flows and to an anonymous reviewer for constructive comments on the manuscript. We also thank Steve Dugdale (University of Birmingham) for his insights and inputs on the revised article.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

This work was funded by the Living with Environmental Change (LWEC) partnership.

References

Afzal

Gagnon

Mansell

(2015) Changes in the variability and periodicity of precipitation in Scotland. Theoretical and Applied Climatology 119(1): 135–159.

Allen

Pereira

Raes

. (1998) Crop evapotranspiration. FAO Irrigation and Drainage Paper no. 56. Rome: FAO.

Battarbee

Shilland

Kernan

. (2014) Recovery of acidified surface waters from acidification in the United Kingdom after twenty years of chemical and biological monitoring (1988–2009). Ecological Indicators 37: 267–273.

Blaney

Criddle

(1950) Determining Water Requirements in Irrigated Areas from Climatological and Irrigation Data. Technical Bulletin no. 1275. Washington, DC: United States Department of Agriculture (USDA), Agricultural Research Service, 59 pp.

Blenkinsop

Fowler

(2007) Changes in European drought characteristics projected by PRUDENCE regional climate models. International Journal of Climatology 27(12): 1595–1610.

Chan

Kendon

Fowler

. (2014) Projected increases in summer and winter UK sub-daily precipitation extremes from high-resolution regional climate models. Environmental Research Letters 9(8): 084019.

Charlton

Arnell

(2014) Assessing the impacts of climate change on river flows in England using the UKCP09 climate change projections. Journal of Hydrology 519: 1723–1738.

Chebud

Naja

Rivero

. (2012) Water quality monitoring using remote sensing and an artificial neural network. Water, Air, & Soil Pollution 223(8): 4875–4887.

Christierson

Vidal

Wade

(2012) Using UKCP09 probabilistic climate information for UK water resource planning. Journal of Hydrology 424: 48–67.

10.

Clark

(2002) Adapting to climate change: Implications for freshwater biodiversity and management in the UK. Freshwater Reviews 2(1): 51–64.

11.

Clark

(2013) Measurements of actual and pan evaporation in the Upper Brue catchment UK: The first 25 years. Weather 6(8): 200–208.

12.

Clews

Durance

Vaugham

. (2010) Juvenile salmonid populations in a temperate river system track synoptic trends in climate. Global Change Biology 16(12): 3271–3283.

13.

Curtis

Battarbee

Monteith

. (2014) The future of upland water ecosystems of the UK in the 21st century: A synthesis. Ecological Indicators 37: 412–430.

14.

Dai

(2013) Increasing drought under global warming in observations and models. Nature Climate Change 3: 52–58.

15.

Darling

Côté

(2008) Quantifying evidence for ecological synergies. Ecology Letters 11(12): 1277–1286.

16.

Des

Clers S

Hughes

Simpson

(2008) Surface water temperature archive for UK freshwater and estuarine sites. Environment Agency Science Report SR070035, 116 pp.

17.

Dugdale

Franssen

Corey

. (2016) Main stem movement of Atlantic salmon parr in response to high river temperature. Ecology of Freshwater Fish 25(3): 429–445.

18.

Durance

Ormerod

(2007) Climate change effects on upland stream macroinvetebrates over a 25-year period. Global Change Biology 13(5): 942–957.

19.

Durance

Ormerod

(2009) Trends in water quality and discharge confound long-term effects of river macroinvetebrates. Freshwater Biology 54(2): 388–405.

20.

Durance

Ormerod

(2010) Evidence for the role of climate in the extinction of a cool-water triclad. Journal of the North American Benthological Society 29(4): 1367–1378.

21.

Fausch

Torgersen

Baxter

. (2002) Landscapes to riverscapes: Bridging the gap between research and conservation of stream fishes. BioScience 52(6): 483–498.

22.

Federer

Vorosmarty

Fekete

(1996) Intercomparison of methods for calculating potential evapotranspiration in regional and global water balance models. Water Resources Research 32(2): 3215–2321.

23.

Fowler

Wilby

(2010) Detecting changes in seasonal precipitation extremes using regional climate model projections: Implications for managing fluvial flood risk. Water Resources Research 46(3): W03525.

24.

Fowler

Ekström

Blenkinsop

. (2007) Estimating change in extreme European precipitation using a multimodel ensemble. Journal of Geophysical Research 112(D18): D18104.

25.

Fung

Orr

Charlton

(2015) Research resource review. Progress in Physical Geography 39(1): 130–134.

26.

Fung

Watts

Lopez

. (2013) Using large climate ensembles to plan or the hydrological impact of climate change in the freshwater environment. Water Resources Management 27(4): 1063–1084.

27.

Garner

Hannah

Sadler

. (2014a) River temperature regimes of England and Wales: Spatial patterns, inter-annual variability and climatic sensitivity. Hydrological Processes 28(22): 5583–5598.

28.

Garner

Malcolm

Sadler

. (2014b) What causes cooling water temperature gradients in a forested stream reach? Hydrology and Earth System Sciences 18(12): 6441–6472.

29.

Garner

Malcolm

Sadler

. (2015a) Inter-annual variability in the effects of riparian woodland on micro-climate, energy exchanges and water temperature of an upland Scottish stream. Hydrological Processes 29(6): 1080–1095.

30.

Garner

Van Loon

Prudhomme

. (2015b) Hydroclimatology of extreme river flows. Freshwater Biology 60(12): 2461–2476.

31.

Hannah

Garner

(2015) River water temperature in the United Kingdom: Changes over the 20th century and possible changes over the 21st century. Progress in Physical Geography 39(1): 68–92.

32.

Hannaford

Marsh

(2008) High-flow and flood trends in a network of undisturbed catchments in the UK. International Journal of Climatology 28(10): 1325–1338.

33.

Heathwaite

(2010) Multiple stressors on water availability at global to catchment scales: Understanding human impact on nutrient cycles to protect water quality and water availability in the long term. Freshwater Biology 55(S1): 241–257.

34.

Hering

Carvalho

Argillier

. (2015) Managing aquatic ecosystems and water resources under multiple stress – An introduction to the MARS project. Science of the Total Environment 503–504: 10–21.

35.

Herrera-Pantoja

Hiscock

(2008) The effects of climate change on potential groundwater recharge in Great Britain. Hydrological Processes 22(1): 73–86.

36.

Hershkovitz

Dahm

Lorenz

. (2015) A multi-trait approach for the identification and protection of European freshwater species that are potentially vulnerable to the impacts of climate change. Ecological Indicators 50: 150–160.

37.

Hough

Jones

RJA

(1997) The United Kingdom Meteorological Office rainfall and evaporation calculation system: MORECS version 2.0 – an overview. Hydrology and Earth System Sciences 1(2): 227–239.

38.

Howden

NJK

Burt

Worrall

. (2010) Nitrate concentrations and fluxes in the River Thames over 140 years (1868–2008): Are increases irreversible? Hydrological Processes 24(18): 2657–2662.

39.

Jackson

(2012) Future flows and groundwater levels: R-groundwater model summary. Report no. CR/12/105 N. Nottingham: British Geological Survey.

40.

Jackson

Bloomfield

Mackay

(2015) Evidence for changes in historic and future groundwater levels in the UK. Progress in Physical Geography 39(1): 49–67.

41.

Jackson

Meister

Prudhomme

(2011) Modelling the effects of climate change and its uncertainty on UK Chalk groundwater resources from an ensemble of global climate model projections. Journal of Hydrology 399(1–2): 12–28.

42.

Jacobs

AFG

Heusinkveld

Holtslag

AAM

(2009) Eighty years of meteorological observations at Wageningen, the Netherlands: Precipitation and evapotranspiration. International Journal of Climatology 30(9): 1315–1321.

43.

Jenkins

Murphy

Sexton

. (2002) UK climate projections: Briefing report. Exeter: Met Office Hadley Centre.

44.

Jenkins

Perry

Prior

(2008) The Climate of the United Kingdom and Recent Trends. Exeter: Met Office Hadley Centre.

45.

Jensen

Haise

(1963) Estimating evapotranspiration from solar radiation. Proceedings of the American Society of Civil Engineers, Journal of the Irrigation and Drainage Division 89: 15–41.

46.

Johnson

Wilby

(2015) Seeing the landscape for the trees: Metrics to guide riparian shade management in river catchments. Water Resources Research 51(5): 3754–3769.

47.

Johnson

Wilby

Toone

(2014) Inferring air-water temperature relationships from river and catchment properties. Hydrological Processes 28(6): 2912–2928.

48.

Jones

Blenkinsop

Fowler

. (2014) Objective classification of extreme rainfall regions for the UK and updated estimates of trends in regional extreme rainfall. International Journal of Climatology 34(3): 751–765.

49.

Jones

Murphy

Noguer

. (1997) Simulation of climate change over Europe using a nested regional-climate model. II: Comparison of driving and regional model responses to a doubling ofcarbon dioxide concentration. Quarterly Journal of the Royal Meteorological Society 123: 265–292.

50.

Jordan

(2013) An Ecosystem Approach to Sustainable Agriculture. Dordrecht, Netherlands: Springer.

51.

Jung

Reichstein

Ciais

. (2010) Recent decline in the global land evapotranspiration trend due to limited moisture supply. Nature 467: 951–954.

52.

Kay

Bell

Blyth

. (2013) A hydrological perspective on evaporation: Historical trends and future projections in Britain. Journal of Water and Climate Change 4(3): 193–208.

53.

Kay

Crooks

Davies

. (2014a) Probabilistic impacts of climate change on flood frequency using response surfaces I: England and Wales. Regional Environmental Change 14(3): 1215–1227.

54.

Kay

Crooks

Davies

. (2014b) Probabilistic impacts of climate change on flood frequency using response surfaces II: Scotland. Regional Environmental Change 14(3): 1243–1255.

55.

Kendon

Roberts

Fowler

. (2014) Heavier downpours with climate change revealed by weather forecast resolution model. Nature Climate Change 4: 570–576.

56.

Kendon

Roberts

Seniro

. (2012) Realism of rainfall in a very high-resolution climate model. Journal of Climate 25: 5791–5806.

57.

Kosanic

Harrison

Anderson

. (2014) Present and historical climate variability in South West England. Climatic Change 124(1): 221–237.

58.

Kurylyk

MacQuarrie

KTB

Voss

(2014) Climate change impacts on the temperature and magnitude of groundwater discharge from shallow unconfined aquifers. Water Resources Research 50(4): 3253–3274.

59.

Laize

CLR

Acreman

Schneider

. (2014) Projected flow alteration and ecological risk for pan-European rivers. River Research and Applications 30(3): 99–314.

60.

Lavers

Hannah

Bradley

(2015) Connecting large-scale atmospheric circulation, river flow and groundwater levels in a Chalk catchment in southern England. Journal of Hydrology 523: 79–189.

61.

Ledbetter

Prudhomme

Arnell

(2012) A method for incorporating climate variability in climate change impact assessments: Sensitivity of river flows in the Eden catchment to precipitation scenarios. Climatic Change 113(3): 803–823.

62.

Lester

Barton

. (2014) Predicting the likely response of data-poor ecosystems to climate change using space-for-time substitution across domains. Global Change Biology 20(11): 3471–3481.

63.

Malcolm

Gibbins

Fryer

. (2014) The influence of forestry on acidification and recovery: Insights from long-term hydrochemical and invertebrate data. Ecological Indicators 37(Part B): 317–329.

64.

Maraun

Wetterhal

Ireson

. (2010) Precipitation downscaling under climate change. Recent developments to bridge the gap between dynamical models and the end users. Reviews of Geophysics 48(3): 1–38.

65.

Marsh

Harvey

(2012) The Thames flood series: A lack of trend in flood magnitude and a decline in maximum levels. Hydrology Research 43(3): 203–214.

66.

Matthaei

Piggott

Townsend

(2010) Multiple stressors in agricultural streams: Interactions among sediment addition, nutrient enrichment and water abstraction. Journal of Applied Ecology 47(3): 639–649.

67.

Montieth

Evans

Henrys

. (2014) Trends in the hydrochemistry of acid-sensitive waters in the UK 1988–2008. Ecological Indicators 37(Part B): 287–303.

68.

Muchan

Lewis

Hannaford

. (2015) The winter storms of 2013/2014 in the UK: Hydrological responses and impacts. Weather 70(2): 55–61.

69.

Murphy

Sexton

DMH

Jenkins

. (2009) UK climate projections science report: Climate change projections. Exeter: Met Office Hadley Centre.

70.

Nakićenović

Swart

(2000) Special report on emissions scenarios. Cambridge: Cambridge University Press.

71.

Navarro-Ortega

Acuña

Bellin

. (2015) Managing the effects of multiple stressors on aquatic ecosystems under water scarcity. The GLOBAQUA project. Science of the Total Environment 503–504: 3–9.

72.

Ormerod

Dobson

Hildrew

. (2010) Multiple stressors in freshwater ecosystems. Freshwater Biology 55(S1): 1–4.

73.

Orr

Simpson

des Clers

. (2015) Detecting changing river temperatures in England and Wales. Hydrological Processes 29(5): 752–766.

74.

Pittock

(2009) Lessons for climate change adaptation from better management of rivers. Climate and Development 1(3): 194–211.

75.

Preston

(2002) Spatial patterns in benthic macroinvertebrate biodiversity of Chesapeake Bay, USA (1984–1999): Association with water quality and sediment toxicity. Environmental Toxicology and Chemistry 21(1): 151–162.

76.

Priestley

CHB

Taylor

(1972) On the assessment of surface heat flux and evaporation using large-scale parameters. Monthly Weather Review 100(2): 81–92.

77.

Prosdocimi

Kjeldsen

Svensson

(2014) Non-stationarity in annual and seasonal series of peak flow and precipitation in the UK. Natural Hazards and Earth System Sciences 14(5): 1125–1144.

78.

Prudhomme

Williamson

(2013) Derivation of RCM-driven potential evapotranspiration for hydrological climate change impact analysis in Great Britain: A comparison of methods and associated uncertainty in future projections. Hydrology and Earth System Sciences 17(4): 1365–1377.

79.

Prudhomme

Crooks

Kay

. (2013a) Climate change and river flooding: Part 1 classifying the sensitivity of British catchments. Climatic Change 119(3): 933–948.

80.

Prudhomme

Giuntoli

Robinson

. (2014) Hydrological droughts in the 21st century hotspots and uncertainties from a global multimodel ensemble project. Proceedings of the National Academy of Sciences of the United States of America 111(9): 3262–3167.

81.

Prudhomme

Jakob

Svensson

(2003) Uncertainty and climate change impact on the flood regime of small UK catchments. Journal of Hydrology 277(1–2): 1–23.

82.

Prudhomme

Kay

Crooks

. (2013b) Climate change and river flooding: Part 2 sensitivity characterisation of British catchments and example vulnerability assessments. Climatic Change 119(3): 949–964.

83.

Prudhomme

Young

Watts

. (2012) The drying up of Britain? A national estimate of changes in seasonal river flows from 11 Regional Climate Model simulations. Hydrological Processes 26(7): 1115–1118.

84.

Rahiz

New

(2013) 21st century drought scenarios for the UK. Water Resources Management 27(4): 1039–1061.

85.

Ramesan

Bellerby

Frostick

(2014) Hydrological modelling using data from monthly GCMs in a regional catchment. Hydrological Processes 28(8): 3241–3263.

86.

Riahi

Rao

Krey

. (2011) RCP 8.5—A scenario of comparatively high greenhouse gas emissions. Climatic Change 109: 33–57.

87.

Rivett

Turner

Glibbery

. (2012) The legacy of chlorinated solvents in the Birmingham aquifer, UK: Observations spanning three decades and the challenge of future urban groundwater development. Journal of Contaminant Hydrology 140–141: 107–123.

88.

Sanderson

Wiltshire

Betts

(2012) Projected changes in water availability in the United Kingdom. Water Resources Research 48(8): W08512.

89.

Sheffield

Eric

Roderick

(2012) Little change in global drought over the past 60 years. Nature 491: 435–438.

90.

Simpson

Jones

(2014) Analysis of UK precipitation extremes derived from Met Office gridded data. International Journal of Climatology 34(7): 2438–2449.

91.

Sivapalan

Blöschl

Zhang

. (2003) Downward approach to hydrological prediction. Hydrological Processes 17(11): 2101–2111.

92.

Smokorowski

Bergeron

Boisclair

. (2011) NSERC’s HydroNet: A national research network to promote sustainable hydropower and healthy aquatic ecosystems. Fisheries 36(10): 480–488.

93.

Stevens

Clark

Nucholls

(2014) Trends in reported flooding in the UK: 1884–2013. Hydrological Sciences Journal 61(1): 50–63.

94.

Taylor

Scanlon

Doll

. (2015) Ground water and climate change. Nature Climate Change 3: 332–329.

95.

Thornthwaite

(1948) An approach toward a rational classification of climate. Geographical Review 38(1): 55–94.

96.

Townsend

Uhlmann

Matthaei

(2008) Individual and combined responses of stream ecosystems to multiple stressors. Journal of Applied Ecology 45(6): 1810–1819.

97.

Turc

(1961) Evaluation des besoins en eau d’irrigation, evapotranspiration potentielle. Annales Agronomiques 12(1): 13–49.

98.

Van den Hoof

Vidale

Verhgoef

. (2013) Improved evaporative flux partitioning and carbon flux in the land surface model JULES: Impact on the simulation of land surface processes in temperature Europe. Agricultural and Forest Meteorology 181: 108–124.

99.

Van Loon

(2015) Hydrological drought explained. WIREs Water 2(4): 359–392.

100.

Vatland

Gresswell

Poole

(2015) Quantifying stream thermal regimes at multiple scales: Combining thermal infrared imagery and stationary stream temperature data in a novel modeling framework. Water Resources Research 51(1): 31–46.

101.

Vaughan

Ormerod

(2014) Linking inter-decadal changes in British river ecosystems to water quality and climate dynamics. Global Change Biology 20(9): 2725–2740.

102.

Vidal

Wade

(2009) A multimodel assessment of future climatological droughts in the United Kingdom. International Journal of Climatology 29(14): 2056–2071.

103.

Watts

Anderson

(eds) (2013) A climate change report card for water. LWEC report card. Available at: http://www.nerc.ac.uk/research/partnerships/ride/lwec/report-cards/water/ (accessed 17 November 2016).

104.

Watts

Battarbee

Bloomfield

. (2015b) Climate change and water in the UK – past changes and future prospects. Progress in Physical Geography 39(1): 6–28.

105.

Watts

Hannah

Watkinson

(2015a) Introduction to the special issue on the impact of climate change on water in the UK. Progress in Physical Geography 39(1): 3–5.

106.

Webb

Walling

(1992) Long-term water temperature behaviour and trends in a Devon, UK, river system. Hydrological Sciences Journal 37(6): 567–580.

107.

Wilby

Quinn

(2013) Reconstructing multi-decadal variations in fluvial flood risk using atmospheric circulation patterns. Journal of Hydrology 487: 9–121.

108.

Wilby

Orr

Watts

. (2010) Evidence needed to manage freshwater ecosystems in a changing climate: Turning adaptation principles into practice. Science of the Total Environment 408(19): 4150–4164.

109.

Wilby

Wigley

TML

Conway

. (1998) Statistical downscaling of general circulation output: A comparison of models. Water Resources Research 34(11): 2995–3008.

110.

Wood

Leung

Sridhar

. (2004) Hydrologic implications of dynamical and statistical approaches to downscaling climate model outputs. Climatic Change 62(1): 189–216.

111.

Zhang

Hiscock

(2013) Application of MT3DMS and geographic information system to evaluation of groundwater contamination in the Sherwood Sandstone aquifer, UK. Water Air and Soil Pollution 224(2): 1438.