How will climate change modify river flow regimes in Europe?

Worldwide, flow regimes are being modified by various anthropogenic impacts and climate change induces an additional risk. Rising temperatures, declining snow cover and changing precipitation patterns will interact differently at different locations. Consequently, in distinct climate zones, unequal consequences can be expected in matters of water stress, flood risk, water quality, and food security. In particular, river ecosystems and their vital ecosystem services will be compromised as their species richness and composition have evolved over long time under natural flow conditions. This study aims at evaluating the exclusive impacts of climate change on river flow regimes in Europe. Various flow characteristics are taken into consideration and diverse dynamics are identified for each distinct climate zone in Europe. In order to simulate present-day natural flow regimes and future flow regimes under climate change, the global hydrology model WaterGAP3 is applied. All calculations for current and future conditions (2050s) are carried out on a 5' × 5' European grid. To address uncertainty, bias-corrected climate forcing data of three different global climate models are used to drive WaterGAP3. Finally, the hydrological alterations of different flow characteristics are quantified by the Indicators of Hydrological Alteration approach. Results of our analysis indicate that on the European scale, climate change can be expected to modify flow regimes remarkably. This is especially the case in the Mediterranean (due to drier conditions with reduced precipitation across the year) and in the boreal climate zone (due to reduced snowmelt, increased precipitation, and strong temperature rises). In the temperate climate zone, impacts increase from oceanic to continental. Regarding single flow characteristics, strongest impacts on timing were found for the boreal climate zone. This applies for both high and low flows. Flow magnitudes, in turn, will be predominantly altered in the Mediterranean but also in the Northern climates. At the end of this study, typical future flow regimes under climate change are illustrated for each climate zone

Evaluating hydrometric networks for prediction in ungauged basins: a new methodology and its application to England and Wales

Flow estimates for ungauged catchments are often derived through regionalisation methods, which enable data transfer from a pool of hydrologically similar catchments with existing gauging stations (i.e., pooling-groups). This paper presents a methodology for indexing the utility of gauged catchments within widely used pooling-group methodologies for high and low flow estimation; this methodology is then used as the basis for a network evaluation strategy. The utility of monitoring stations is assessed using catchment properties and a parallel, but independent, appraisal of the quality of gauging station data, which considers hydrometric performance, anthropogenic disturbances and record length. Results from the application of the method to a national network of over 1,100 gauging stations in England and Wales are presented. First, the method is used to appraise the fitness-for-purpose of the network for regionalisation. The method is then used to identify gauges which monitor catchments with high potential for regionalisation, but which are deficient in terms of data quality – where upgrades in hydrometric performance would yield the greatest benefits. Finally, gauging stations with limited value for regionalisation, given the pooling-group criteria employed, are identified. Alongside a wider review of other uses of the network, this analysis could inform a judicious approach to network rationalisation

The identification of hydrological indices for the characterization of macroinvertebrate community response to flow regime variability

The importance of flow regime variability for maintaining ecological functioning and integrity of river ecosystems has been firmly established in both natural and anthropogenically modified systems. In this paper we examine river flow regimes across lowland catchments in eastern England using 47 variables, including those derived using the Indicators of Hydrologic Alteration (IHA) software. A Principal Components Analysis (PCA) method was used to identify redundant hydrological variables and those that best characterised the hydrological series (1986-2005). A small number of variables (< 6 variables) characterised up to 95% of the statistical variability in the flow series. The hydrological processes and conditions that the variables represent were found to be significant in structuring the instream macroinvertebrate community LIFE scores at both the family- and species-level. However, hydrological variables only account for a relatively small proportion of the total ecological variability (typically <10%). The research indicates that a range of other factors, including channel morphology and anthropogenic modification of instream habitats, structure riverine macroinvertebrate communities in addition to hydrology. These factors need to be considered in future environmental flow studies to enable the characterisation of baseline/reference conditions for management and restoration purposes

Climatic and catchment drivers of monthly water temperature of UK rivers

Water temperature is a key control on many river processes including ecology and biogeochemistry. Consequently, the effect of climate change on river and stream temperatures is a major scientific and practical concern. River thermal sensitivity to climate change/ variability is controlled by complex drivers that need to be unravelled to better understanding patterns of spatio-temporal variability and the relative importance of different controls to inform water and land management, specially climate change mitigation and adaptations strategies. To address these research gaps, we aim: (1) to quantify the relative importance of different climatic drivers of water temperature across a set of UK benchmark monitoring sites; and (2) to assess the effect of basin properties as modifiers of the climate-temperature relationships. For the UK, previous water temperature studies focussed either on a limited number of monitoring sites or climatic drivers. Water temperature data were collated across several long-term UK national capability projects, totalling 35 sites with a nationwide spread. Data were processed to create seasonal water temperature series (i.e. 3-month averages as follow: December - February for winter, March - May spring, June - August summer, and September - November autumn). Modelled climate data [daily, 1-km gridded forcing data for the Joint UL Land-Environment Simulator (JULES) for air temperature, short and long wave radiation, wind speed, specific humidity, and precipitation] were extracted for each of the water temperature site and seasonal averages were derived also. We modelled the response of water temperature (dependent variable) to the six climatic variables (predictors). One model per season was fitted to investigate season-specific controls; and one model was fitted for all seasons together to investigate the overall response (i.e. a total of five models). Methodologically, the study used a combination of two statistical techniques that are quite novel in the field: (1) a multi-level modelling approach was chosen to account for the hierarchical structure in the data sets (i.e. observations at a site, sites on a river); (2) model selection was based on an information theory criterion within a multi-model inference framework (i.e. sets of good models were selected rather a single best model). This approach showed that all six climatic variables exert some influence in some or all models. The most influential were air temperature for all seasonal models, short wave radiation for all seasons except summer, specific humidity for winter, wind speed and precipitation for summer. Spatial patterns were then investigated by mapping site-specific responses. These patterns were crossedchecked with selected basin properties in order to identify in what extent basins act as modifiers of the climate/ water temperature response

Increasing risk of ecological change to major rivers of the world with global warming

The hydrological characteristics of a river, including the magnitude and timing of high and low flows, are important determinants of its ecological functioning. Climate change will alter these characteristics, triggering ecological changes in river ecosystems. This study assesses risks of ecological change in 321 major river basins across the globe due to global warming relative to pre-industrial conditions of 1.0, 1.5, 2.0 and 3.0°C. Risks associated with climate-driven changes to high and low flows, relative to baseline (1980–2010; 0.6°C warming), are investigated using simulations from nine global hydrological models forced with climate projections from five global climate models, resulting in an ensemble of 14,445 baseline-scenario members for each warming scenario (9 × 5 × 321). At the global-scale, the likelihood of high risks of significant ecological change in both high and low flows increase with global warming: across all basins there is a medium-high risk of change in high (low) flows in 21.4% (22.4%) of ensemble members for 1.0°C warming, increasing to 61.5% (63.2%) for 3.0°C. Risks are particularly pronounced for low flows at 3.0°C for many rivers in South America, southern Africa, Australia, southern Europe and central and eastern USA. Results suggest that boreal regions are least likely to see significant ecological change due to modified river flows but this may be partly the result of the exclusion of processes such as permafrost dynamics from most global hydrological models. The study highlights the ecological fragility and spatial heterogeneity of the risks that unmitigated climate change poses to global river ecosystems

Projected flow alteration and ecological risk for pan-European rivers

Projection of future changes in river flow regimes and their impact on river ecosystem health is a major research challenge. This paper assesses the implications of projected future shifts in river flows on in-stream and riparian ecosystems at the pan-European scale by developing a new methodology to quantify ecological risk due to flow alteration (ERFA). The river network was modelled as 33 668 cells (5′ longitude × 5′ latitude). For each cell, modelled monthly flows were generated for an ensemble of 10 scenarios for the 2050s and for the study baseline (naturalized flows for 1961–1990). These future scenarios consist of combinations of two climate scenarios and four socio-economic water-use scenarios (with a main driver of economy, policy, security or sustainability). Environmental flow implications are assessed using the new ERFA methodology, based on a set of monthly flow regime indicators (MFRIs). Differences in MFRIs between scenarios and baseline are calculated to derive ERFA classes (no, low, medium and high risk), which are based on the number of indicators significantly different from the baseline. ERFA classes are presented as colour-coded pan-European maps. Results are consistent between scenarios and show that European river ecosystems are under significant threat with about two-thirds at medium or high risk of change. Four main zones were identified (from highest to lowest risk severity): (i) Mediterranean rim, southwest part of Eastern Europe and Western Asia; (ii) Northern Europe and northeast part of Eastern Europe; (iii) Western and Eastern Europe; and (iv) inland North Africa. Patterns of flow alteration risk are driven by climate-induced change, with socio-economics as a secondary factor. These flow alterations could be manifested as changes to species and communities, and loss of current ecosystem functions and services