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We examined how communities of macroinvertebrates occurring in functional process zones (FPZs) are affected by the location of FPZs in the river continuum. We delineated FPZs for three rivers displaying significant disparities in elevation, annual precipitation, valley shape, and other valley‐scale hydrogeomorphic variables. We extracted corresponding macroinvertebrate community data from the US National Water Quality Monitoring Council database and matched it to the stream order (SO) and FPZ delineations. We examined community structure in the three rivers by partitioning the variances associated with the FPZ and SO delineations. Then, we examined community variation as patterns of beta‐diversity for communities of FPZs in different SOs. In total, 23 FPZ‐SO configurations were examined. SO and FPZ delineations contributed similarly to the variance in the structure of macroinvertebrate communities. Taxa turnover accounted for the majority of the compositional change in communities of FPZs along the river continuum, while the functional composition showed primarily a nested structure. Pairwise comparison of communities for each FPZ along the river continuum showed that significant differences in community composition occurred at high SO in the three examined rivers. In this manuscript, we show that communities of FPZs are only partially comparable along the river continuum as significant compositional changes occur when comparing communities of FPZs in distant SOs. We bring, therefore, new elements to improve the interpretation of the River Ecosystem Synthesis concept that can have wider implications for understanding the biocomplexity of hydrogeomorphic patchiness in river networks.

Climate change has pronounced impacts on water resources, especially in arid regions. This study aims at assessing the impacts of climate change on streamflow of the Wadi Halilrood Basin which feeds the Jazmorian wetland in southeastern Iran. To simulate streamflow and hydrological components in the future periods (2030–2059 and 2070–2099), projections for the emission scenarios RCP4.5 and RCP8.5 from 11 global-regional climate models and two bias correction methods are used as input data for a hydrologic model that represents the daily streamflow with good accuracy (NSE: 0.76, PBIAS: 4.7, KGE: 0.87). The results indicate a slight increase of streamflow in January and March, due to the higher intensity of precipitation. However, according to the predicted flow duration curves, a decrease for high and very high flow and no remarkable changes for middle, low and very low flow is found under both emission scenarios for both future periods. Compared to the simulated hydrological components for the baseline, a slight increase of evapotranspiration of around 6 mm (4%) and 2 mm (

Climate change impacts on the water cycle can severely affect regions that rely on groundwater to meet their water demands in the mid- to long-term. In the Lake Tana basin, Ethiopia, discharge regimes are dominated by groundwater. We assess the impacts of climate change on the groundwater contribution to streamflow (GWQ) and other major water balance components in two tributary catchments of Lake Tana. Based on an ensemble of 35 bias-corrected regional climate models and a hydrologic catchment model, likely changes under two representative concentration pathways (RCP4.5 and 8.5) are assessed. No or only slight changes in rainfall depth are expected, but the number of rainy days is expected to decrease. Compared to the baseline average, GWQ is projected to decrease whereas surface runoff is projected to increase. Hence, rainfall trends alone are not revealing future water availability and may even be misleading, if regions rely heavily on groundwater. HIGHLIGHTS Change in the rainfall intensity affects the availability of groundwater in a catchment.; Rainfall projections from different global and regional climate models show disparities among each other.; The projected actual evapotranspiration is expected to decrease in the future for the study region due to less water availability.

Water resources are precious in arid and semi-arid areas such as the Wadis of Iran. To sustainably manage these limited water resources, the residents of the Iranian Wadis have been traditionally using several water use systems (WUSs) which affect natural hydrological processes. In this study, WUSs and soil and water conservation measures (SWCMs) were integrated in a hydrological model of the Halilrood Basin in Iran. The Soil and Water Assessment Tool (SWAT) model was used to simulate the hydrological processes between 1993 and 2009 at daily time scale. To assess the importance of WUSs and SWCMs, we compared a model setup without WUSs and SWCMs (Default model) with a model setup with WUSs and SWCMs (WUS-SWCM model). When compared to the observed daily stream flow, the number of acceptable calibration runs as defined by the performance thresholds (Nash-Sutcliffe efficiency (NSE)≥0.68, −25%≤percent bias (PBIAS)≤25% and ratio of standard deviation (RSR)≤0.56) is 177 for the Default model and 1945 for the WUS-SWCM model. Also, the average Kling-Gupta efficiency (KGE) of acceptable calibration runs for the WUS-SWCM model is higher in both calibration and validation periods. When WUSs and SWCMs are implemented, surface runoff (between 30% and 99%) and water yield (between 0 and 18%) decreased in all sub-basins. Moreover, SWCMs lead to a higher contribution of groundwater flow to the channel and compensate for the extracted water by WUSs from the shallow aquifer. In summary, implementing WUSs and SWCMs in the SWAT model enhances model plausibility significantly.

A recent global meta‐analysis reported a decrease in terrestrial but increase in freshwater insect abundance and biomass (van Klink et al., Science 368, p. 417). The authors suggested that water quality has been improving, thereby challenging recent reports documenting drastic global declines in freshwater biodiversity. We raise two major concerns with the meta‐analysis and suggest that these account for the discrepancy with the declines reported elsewhere. First, total abundance and biomass alone are poor indicators of the status of freshwater insect assemblages, and the observed differences may well have been driven by the replacement of sensitive species with tolerant ones. Second, many of the datasets poorly represent global trends and reflect responses to local conditions or nonrandom site selection. We conclude that the results of the meta‐analysis should not be considered indicative of an overall improvement in the condition of freshwater ecosystems. This article is categorized under: Water and Life > Conservation, Management, and Awareness, Relying on abundance or biomass and examining nonrepresentative datasets limits our ability to infer the condition of freshwater insect communities globally. Photo by Jeremy Monroe, Freshwaters Illustrated: a caddisfly larva from an Oregon Coastal stream, USA (Limnephilidae: Dicosmoecus sp.)., Federal Agency for Nature Conservation (BfN) http://dx.doi.org/10.13039/100010606, NSF Macrosystems Biology Program, Leibniz‐Gemeinschaft http://dx.doi.org/10.13039/501100001664

For discussing and planning sustainable land management of river basins, stakeholders need suitable information on spatio-temporal patterns of natural processes and human actions. This study shows an approach to use ecohydrological modelling results for assessing water-related ecosystem services in three lowland river basins in Western Siberia. Based on the results of the ecohydrological model SWAT (Soil and Water Assessment Tool, Arnold et al., 1998), simulated output variables were used as indicators for the two regulating services water flow regulation and erosion regulation. The model results were translated into a relative ecosystem service valuation scale, which facilitates the comparison of different ecosystem services and which serves as the base for the applied mapping approach. The ecosystem service maps show different spatial and seasonal patterns. Although the daily modelling results were aggregated to seasonal maps to generate an understandable amount of information for stakeholders, differences can be depicted: during snowmelt, low regulation can be determined, especially for water flow regulation, but a very high regulation was calculated for the vegetation period during summer and for the winter period. Erosion regulation is high in two basins during all seasons. Spatio-temporal differences were modelled only for the largest basin. The SWAT model serves as a suitable quantification method for the assessment of the selected water-related regulating services.

In this study, we analyse possible future climatic changes in three catchments, namely, Pyshma, Vagai and Loktinka located in the Western Siberian lowland region, and the resulting impact on hydrological regimes. It involved downscaling the GCM outputs based on the established statistical relationship between large-scale atmospheric variables and station data and simulating the effects of climate change on hydrological regimes via hydrological modelling. This was done for RCP 2.6, 4.5 and 8.5 based on second-generation Canadian Earth System Model used in the IPCC fifth assessment report. This paper provides the first climate change projections on a local scale in these catchments. The statistical downscaling showed that there will be an increase in both maximum and minimum temperature at all stations under all scenarios. The mean annual daily precipitation increased in Loktinka and Pyshma basins under all scenarios, but there was no clear trend in Vagai basin. The possible increase in annual precipitation is mostly due to the projected increase in autumn and winter precipitation. Annual streamflow tends to increase in all catchments under all scenarios.

Understanding and quantifying the effects of future climate change is currently one of the most pressing challenges in science and of high relevance for society. Most future climate change studies consider changes between arbitrary time periods. We specify these time periods by splitting climate-change impacted streamflow time series at instances of highest change, by using statistical tests. We used the daily streamflow from 2000 to 2099 simulated from a comprehensive ensemble of the EURO-CORDEX climate change data in three basins across Germany (Treene, lowland; Kinzig, mid-range mountain; and Ammer, pre-alpine). Change points in each basin were detected by using six change point tests. The robustness of changes was analyzed with a bootstrapping procedure. A set of 32 Indicators of Hydrologic Alteration (IHA) was used to examine characteristics of hydrologic changes in the simulated discharge time series between pre- and post-change-point period in absolute change and in deviation of the Range of Variability Approach (RVA). The results show that the occurrence of change points due to climate change is spread throughout the decades, but strongly clustered in the current and upcoming decade. The selection of global and regional climate models impacts the occurrence of change points to a greater extent than the choice of greenhouse gas emission scenarios and bias correction method. The highest significant alteration of IHA occurs in the lowland-, less in the alpine- and least in the mid-range mountain catchment. The transition of hydrologic regimes to an alternative state after the identified change points is likely to occur because the majority of indicators move out of the current state of RVA. We further notice ecoregion-dependent changes in summer discharges and extreme low flows, which increase in the lowland and decrease in the pre-alpine catchment. This may have a detrimental effect on local aquatic communities. We conclude that the combined analysis of simulated climate scenarios, change points and IHA enables a better interpretability of potential future hydrological changes both in timing and severity and provides an early warning signal of changes for climate change mitigation.

Freshwater species are adapted to and depend on various discharge conditions, such as 32 indicators of hydrologic alteration (IHA). Knowing how these indicators will be altered under climate change is essential for predicting species response and to develop mitigation concepts. The simulation of IHA under climate change is subject to considerable uncertainties which should be considered to obtain credible and robust predictions. Therefore, we investigated the major uncertainties inherent in climate change data and processing: general circulation model (GCM) and regional climate model (RCM) choice, representative concentration pathway (RCP) scenario, bias correction (BC) method, all within three mesoscale catchments in the European ecoregions: Central Plains, Central Highlands, and Alpine. Highest uncertainties were caused by the GCM and RCM choice, followed by the type of BC and the RCP. For the prediction, we reduced these uncertainties tailored to the ideal depiction of the IHA in each ecoregion. Together with a significance test, this enabled a robust depiction of the change in IHA for two future time periods. We found diverging changes within the ecoregions, caused by the complex interaction between precipitation, temperature and the governing catchment hydrological processes. The results provide an important basis for further impact research, especially for ecological freshwater studies.

The relevance of hydrological processes varies in space and time resulting in typical temporal patterns for catchments. Contrasting catchments moreover differ in their catchment metrics. Hydrological models claim to be able to reproduce typical temporal patterns of dominant processes using site-specific model parameters. Thus, patterns of temporal dynamics in dominant modelled processes and their corresponding dominant parameters are a fingerprint of how a model represents the hydrological behaviour of a catchment and how these process patterns vary between contrasting catchments. In this study, we demonstrate how catchment metrics, modelled processes and parameter dominances can be jointly used to characterise catchments. We assess how catchment characteristics are represented in spatio-temporal process dynamics in models and how to understand the reasons for hydrological (dis)similarity among catchments along a landscape gradient. For this purpose, catchment metrics which characterise contrasting landscapes (lowland, mid-range mountain and alpine catchments) are related to dominant processes and parameters which were provided by a temporally resolved sensitivity analysis (TEDPAS) and simulations of a hydrological model. Our study shows that the applied model is able to represent the different processes and their seasonal variability according to the specific hydrological conditions of the study catchments. By analysing catchment metrics, modelled processes and model parameters jointly, we show that the largest differences are identified for the alpine catchment, whilst similarities are found among the other catchments. Following a landscape gradient, high flow phases are dominated by different flow components. In contrast, the model shows groundwater dominance in low flow phases in non-alpine catchments while in the alpine catchment low flows in winter are mainly controlled by snow processes. The joint analysis of catchment metrics, temporal dynamics of dominant processes and parameters can therefore be used to better disentangle similarities and differences among catchments from different landscapes.

Global change has the potential to affect river flow conditions which are fundamental determinants of physical habitats. Predictions of the effects of flow alterations on aquatic biota have mostly been assessed based on species ecological traits (e.g., current preferences), which are difficult to link to quantitative discharge data. Alternatively, we used empirically derived predictive relationships for species’ response to flow to assess the effect of flow alterations due to climate change in two contrasting central European river catchments. Predictive relationships were set up for 294 individual species based on (1) abundance data from 223 sampling sites in the Kinzig lower-mountainous catchment and 67 sites in the Treene lowland catchment, and (2) flow conditions at these sites described by five flow metrics quantifying the duration, frequency, magnitude, timing and rate of flow events using present-day gauging data. Species’ abundances were predicted for three periods: (1) baseline (1998–2017), (2) horizon 2050 (2046–2065) and (3) horizon 2090 (2080–2099) based on these empirical relationships and using high-resolution modeled discharge data for the present and future climate conditions. We compared the differences in predicted abundances among periods for individual species at each site, where the percent change served as a proxy to assess the potential species responses to flow alterations. Climate change was predicted to most strongly affect the low-flow conditions, leading to decreased abundances of species up to −42%. Finally combining the response of all species over all metrics indicated increasing overall species assemblage responses in 98% of the studied river reaches in both projected horizons and were significantly larger in the lower-mountainous Kinzig compared to the lowland Treene catchment. Such quantitative analyses of freshwater taxa responses to flow alterations provide valuable tools for predicting potential climate-change impacts on species abundances and can be applied to any stressor, species, or region. OA gold - CA extern

Current knowledge regarding the flow preferences of benthic stream invertebrates is mostly based on qualitative data or expert knowledge and literature analysis. These established flow preferences are difficult to use in predictions of the effects of global change on aquatic biota. To complement the existing categories, we performed a large-scale analysis on the distribution of stream invertebrates at stream monitoring sites in order to determine their responses to various hydrological conditions. We used 325 invertebrate surveys from environmental agencies at 238 sites paired to 217 gauges across Germany covering a broad range of hydrological conditions. Based on these data, we modelled the respective probabilities of occurrences for 120 benthic invertebrate taxa within this hydrological range using hierarchical logistic regression models. Our analyses revealed that more than one-third of the taxa (18–40%) can be considered as ubiquitous and having a broad hydrological tolerance. Furthermore, 22–41% of the taxa responded to specific ranges of flow conditions with detectable optima. “Duration high flow event” represented the flow parameter that correlated best with the abundance of individual taxa, followed by “rate of change average event”, with 41 and 38% of the taxa showing a peak in their probability of occurrence at specific ranges of these metrics, respectively. The habitat suitability for these taxa may be potentially affected by global change-induced hydrological changes. Quantified hydrological traits of individual taxa might therefore support stream management and enable the prediction of taxa responses to flow alteration. The hydrological traits of stream benthic invertebrates may be used in forecasting studies in central Europe, and the methods used in this study are suitable for application in other regions with different flow regimes.

The USLE is used world-wide to predict soil loss on the field scale from sheet and rill erosion. The slope length (L) factor is derived as its topographical factor. The accuracy of L factor determines the precision of soil loss estimation with USLE. Uncertainties on L factor are caused by DEM resolution and the choice of the processing algorithm. In the present study we made two comparisons to evaluate the effects of DEM horizontal resolution and processing algorithm on the accuracy of the L factor in gently sloped landscapes: one is between the grid cumulating method (GC) and the contributing area method (CA) using D8 flow-routing algorithm, the other is among single (D8, Rho8) and multiple (FD8, FRho8 and DEMON) flow-routing algorithms for processing the contributing area method. In two comparisons, 5 m, 10 m, 25 m, 50 m and 100 m DEM of a 0.88 km2 catchment in the lowland of Northern Germany were applied. The results indicate that L factor calculated with any of the six methods is sensitive to horizontal resolution, which strongly affects the accuracy. With decreasing resolution, correlations of LCA_Rho8 and LCA_D8, LCA_FD8 and LCA_D8, LCA_FD8 and LCA_Rho8 increase while those between DEMON and the other flow-routing algorithms do not change significantly. With decreasing resolution, the difference between LGC_D8 and LCA_D8 is enlarged, while differences between any two flow algorithms using CA did not change significantly. The L factor variation between any two methods is larger on the upslope than the flat valley for the 5 m and 10 m DEM while terrain characteristics are not visible on the 25 m, 50 m and 100 m DEM. The L factor also depends on the computation method. LGC_D8 is approximately half of LCA. It is concluded that DEM horizontal resolution is very important for L factor calculation. The most suitable calculation method is LGC_D8 for gently rolling landscapes. This study can be used for selecting a suitable method and DEM resolution for accurate calculation of L factor and soil loss in gently rolling landscapes.

To date, no examples of small- to meso-scale hydrological simulations exist in the southern part of the Western Siberian lowlands, despite intensive agriculture and high vulnerability to climate change. We propose a first simulation approach in which we assess the importance of surface and groundwater processes on hydrological model performance. Therefore, we simulated three catchments, using four different model setups incorporating different landscape characteristics and processes. An objective calibration and comparison framework was applied to assess the different setups which reached very diverse performance: the setups where physically-based surface retention is considered, showed slightly more realistic surface runoff driven peak flows and the setups with a more complex groundwater concept improved the depiction of surface runoff, the recession phase and the contributing baseflow significantly. The best performing, most complex setup was used to assess the prevailing hydrological processes of the lowland with its cold, continental climate in more detail.