Potential impacts of climate change on flow regime and fish habitat in mountain rivers of the south-western Balkans

National-Scale Assessment of Climate Change Impacts on Two Native Freshwater Fish Using a Habitat Suitability Model

Climate change, which has the potential to alter water flow and temperature in aquatic environments, can influence the freshwater fish habitat. This study used an ecological habitat suitability model (EHSM), which integrates hydraulic (water depth and velocity) and physiologic (water temperature) suitability, to investigate the impact of climate change on two native freshwater fish species (Zacco platypus and Nipponocypris koreanus) in South Korea. The model predicted that in 2080 (2076–2085), the decrease in average ecological habitat suitability (EHS) will be higher for N. koreanus (19.2%) than for Z. platypus (9.87%) under the representative concentration pathway (RCP) 8.5 scenario. Under the same condition, EHS for Z. platypus and N. koreanus at 36.5% and 44.4% of 115 sites, respectively, were expected to degrade significantly (p < 0.05). However, the habitat degradation for Z. platypus and N. koreanus was much lower (7.8% and 10.4%, respectively) under the RCP 4.5 scenario, suggesting a preventive measure for carbon dioxide emission. Partial correlation analysis indicated that the number of hot days (i.e., days on which the temperature exceeds the heat stress threshold) is the variable most significantly (p < 0.05) related to EHS changes for both species. This study suggests that the EHSM incorporating the effect of water temperature on the growth and heat stress of fish can be a promising model for the assessment of climate change impacts on habitat suitability for freshwater fish.

Making Room for Our Forthcoming Rivers

This paper provides a schematic, conceptual trip across a set of paradigms that can be adopted to design flood control actions and the associated river setting, including the space allocated to the river. By building on such paradigms, it eventually delineates an integrated approach to identify a socially desirable river setting, under a climate changing reality. The key point addressed is that when residual Risk and Operation, Management and Replacement costs are considered to their full extent, even a basic economic analysis may suggest alternative river settings that can be more attractive, particularly if accompanied by suitable economic-administrative management measures. Emphasis is put on the deep uncertainty characterizing the whole decision problem and on the need for a drastic change of paradigm. The approach proposed can greatly improve current Flood Risk Management Plans responding to the European Flood Directive (Directive 2007/60/EC). It can also help to develop constructive dialogues with stakeholders, while enhancing the understanding of the problem. Although mainly intended to address a conceptual level, it also aims at providing an applicable method.

Unravelling Precipitation Trends in Greece since 1950s Using ERA5 Climate Reanalysis Data

Precipitation is one of the most variable climatic parameters, as it is determined by many physical processes. The spatiotemporal characteristics of precipitation have been significantly affected by climate change during the past decades. Analysis of precipitation trends is challenging, especially in regions such as Greece, which is characterized by complex topography and includes several ungauged areas. With this study, we aim to shed new light on the climatic characteristics and inter-annual trends of precipitation over Greece. For this purpose, we used ERA5 monthly precipitation data from 1950 to 2020 to estimate annual Theil–Sen trends and Mann–Kendall significance over Greece and surrounding areas. Additionally, in order to analyze and model the nonlinear relationships of monthly precipitation time series, we used generalized additive models (GAMs). The results indicated significant declining inter-annual trends of areal precipitation over the study area. Declining trends were more pronounced in winter over western and eastern Greece, but trends in spring, summer and autumn were mostly not significant. GAMs showcased that the trends were generally characterized by nonlinearity and precipitation over the study area presented high inter-decadal variability. Combining the results, we concluded that precipitation did not linearly change during the past 7 decades, but it first increased from the 1950s to the late 1960s, consequently decreased until the early 1990s and, afterwards, presented an increase until 2020 with a smaller rate than the 1950–1960s.

Four Decades of Surface Temperature, Precipitation, and Wind Speed Trends over Lakes of Greece

Climate change is known to affect world’s lakes in many ways. Lake warming is perhaps the most prominent impact of climate change but there is evidence that changes of precipitation and wind speed over the surface of the lakes may also have a significant effect on key limnological processes. With this study we explored the interannual trends of surface temperature, precipitation, and wind speed over 18 lakes of Greece using ERA5-Land data spanning over a period of almost four decades. We used generalized additive models (GAMs) to conduct time-series analysis in order to identify significant trends of change. Our results showed that surface temperature has significantly increased in all lakes with an average rate of change for annual temperature of 0.43 °C decade−1. With regard to precipitation, we identified significant trends for most lakes and particularly we found that precipitation decreased during the first two decades (1981–2000), but since 2000 it increased notably. Finally, wind speed did not show any significant change over the examined period with the exception for one lake. In summary, our work highlights the major climatic changes that have occurred in several freshwater bodies of Greece. Thus, it improves our understanding on how climate change may have impacted the ecology of these important ecosystems and may aid us to identify systems that are more vulnerable to future changes.

Hydrological Response of Natural Mediterranean Watersheds to Forest Fires

Fires are common in forested Mediterranean-climate watersheds. Forest fires cause abrupt land use/cover (LULC) changes affecting soil properties and hydrological processes within and across watersheds. A major forest fire in Attica, Greece, that affected the Lykorrema stream experimental watershed provided the opportunity for an in-depth study of the impact of forest fires on the hydrological balance of natural Mediterranean watersheds. To this end, detailed hydrometeorological data recorded for five years before and for five years after the fire incidence were utilized. SWAT model was also used to consider the potential influence of meteorological conditions temporal variability on the results of the analysis. Specifically, SWAT model was parameterized calibrated and validated for the pre-fire and the post-fire conditions using the corresponding detailed hydrometeorological data for the respective periods. Then the two versions of the model were applied for the entire period providing comprehensive time series for all the flows and storages in the studied watershed. In this way, the post-fire LULC and soil properties changes were the only influencing factors driving the alterations in the hydrological balance allowing an impartial comparison. The obtained results highlighted the considerable impact of forest fires on the watersheds’ hydrological functioning. Specifically, the maximum direct runoff depths and the maximum flow rates were substantially higher in the post-fire conditions. In contrast, actual evapotranspiration was reduced, when the effect of fire was considered. The obtained results indicate that the altered post-fire LULC and soil properties are major drivers of the watershed’s hydrological balance changes. SWAT model performed sufficiently well for both the pre- and post-fire conditions and provided a deeper insight into the impact of forest fires on the hydrological functioning of natural Mediterranean watersheds.

Wet season flood magnitude drives resilience to dry season drought of a euryhaline elasmobranch in a dry-land river

The increase in severity and occurrence of drought from environmental change poses a significant threat to freshwater ecosystems. However, many of the mechanisms by which periodic drought affects aquatic animals are poorly understood. Here we integrated physical, physiological, and behavioural measurements made in the field over a twelve-year period to provide a comprehensive understanding of the factors affecting the loss of body condition of fish in arid rivers, using the Critically Endangered freshwater sawfish (Pristis pristis) in the dryland Fitzroy River, Western Australia, as a model species. Sawfish lost condition throughout the long dry season in all years and had significantly poorer body condition throughout years characterized by low volumes of wet season flooding and little occurrence of overbank flooding. A mechanistic examination of factors leading to this loss of condition using measurements of body temperature, field energetics, and habitat use from telemetry techniques showed that the loss of condition throughout the season was likely due to substantial habitat compression and low productivity in drier years, while high rates of competition were more likely to drive this pattern in wetter years. This information can be used to forecast how climate change and water abstraction will affect aquatic fauna experiencing intermittent drought and can inform management decisions to help mitigate these threats.

Gradients of flow regulation shape community structures of stream fishes and insects within a catchment subject to typhoon events

Alterations in natural flow regimes caused by dams can significantly alter the aquatic habitats of stream organisms. However, few studies have characterized flow regulation to assess its impacts on stream fauna in the context of interannually variable extreme floods. This study aims to understand the variation in stream animals along flow regulation gradients due to hydropower dams in a catchment experiencing typhoons. We observed freshwater fishes and stream insects at fully regulated sites (receiving residual flow), moderately regulated sites (receiving hydropower outflow), and nonregulated site (tributary) in the Mimi River catchment in southern Japan, in summer and winter from 2010 to 2018. We computed indicators of hydrologic alteration (IHA) in each calendar/water (July to June) year from 2007 to 2017 and selected subsets of IHA based on principal component analysis (PCA) and variance inflation factor. The largest variance was mainly explained by minimum discharge levels (e.g., 30-day annual minimum) and flow variability among IHAs, distinguishing the moderately regulated and nonregulated sites from fully regulated sites because of residual flow and suppressed high pulses in the fully regulated sites. Generalized additive models revealed that annual maxima of specific discharge were most significant predictors of fish and insect metrics while its effects were generally inconsistent between summer and winter. Non-metric multidimensional scaling revealed that insect communities were clustered into the regulation extents in both seasons. The differences in winter fauna between the regulated and nonregulated sites, characterized by Ephemeroptera-Plecoptera-Trichoptera abundance, were associated with maximum discharge and high pulse numbers. Fish community variation did not correspond to flow regime gradients. Our findings on mechanistic ecohydrological consequences of various flow regulations, supported by long-term observations, will be useful for river managers attempting to compensate for alterations in flow regime and ecological integrity.

Temperature-Dependent Swimming Performance Differs by Species: Implications for Condition-Specific Competition between Stream Salmonids

Condition-specific competition is a phenomenon by which inter-specific competitive dominance changes as a result of environment, and is an important factor determining species distribution. Congeneric charrs in Hokkaido, Japan, provide one of the best examples of condition-specific competition: Dolly Varden, Salvelinus malma, often dominate in cold streams (6-8°C), whereas white-spotted charr, Salvelinus leucomaenis, dominate in warmer streams (> 10°C). While past laboratory and field experiments have demonstrated the great advantage of white-spotted charr at higher water temperatures, the advantages of Dolly Varden at lower temperature have not always been clear. Here, we examined the effect of water temperature (6°C vs. 12°C) on the swimming ability of the two sympatric charrs using a stamina tunnel. At 6°C, the swimming ability of Dolly Varden was greater than that of white-spotted charr, but no difference was observed at 12°C. These results suggest that the temperature-mediated swimming ability differs between these species, which may explain the coexistence of the closely related species within heterogeneous habitats via condition-specific competition.

Assessment of future hydrologic alteration due to climate change in the Aracthos River basin (NW Greece)

Climate change is a worldwide reality with significant effects on hydrological processes. It has already produce alterations in streamflow regime and is expected to continue in the future. To counteract the climate change impact, a better understanding of its effects is necessary. Hydrological models in combination with Indicators of Hydrologic Alteration (IHA) suppose an up-to-date approach to analyze in detail the impacts of climate change on rivers. In this study, the Soil and Water Assessment Tool (SWAT) model and Indicators of Hydrologic Alteration in Rivers (IAHRIS) software were successfully applied in Aracthos River basin, an agricultural watershed located in the north-western area of Greece. Statistical indices showed an acceptable performance of the SWAT model in both calibration (R² = 0.74, NSE = 0.54, PBIAS = 17.06%) and validation (R² = 0.64, NSE = 0.36, PBIAS = 12.31%) periods on a daily basis. To assess the future hydrologic alteration due to climate change in Aracthos River basin, five Global Climate Models (GFDL-ESM2, HadGEM2-ES, IPSL-CM5A-LR, MIROC-ESM-CHEM and NorESM1-M) were selected and analyzed under two different emission scenarios (RCP 4.5 and RCP 8.5) for a long-term period (2070-2099). Results indicate that precipitation and flow is expected to be reduced and maximum and minimum temperature to be increased, compared to the historical period (1970-1999). IHA, obtained from IAHRIS software, revealed that flow regime can undergo a severe alteration, mainly on droughts that are expected to be more significant and longer. All these future hydrologic alterations could have negative consequences on the Aracthos River and its surroundings. The increase of droughts duration in combination with the reduction of flows and the alteration of seasonality can affect the resilience of riverine species and it can produce the loss of hydraulic and environmental diversity. Therefore, this study provides a useful tool for decision makers to develop strategies against the impact of climate change.

A baseline assessment of hydrologic alteration degree for the Mexican catchments at gauged rivers (2016)

River regime has been modified in several freshwater bodies around the world. This alteration has led to species loss, water pollution, higher or lesser economic profits, changes in magnitude, timing, duration and rate change of flow, among others. Thus, hydrologic alteration assessment allows evaluating the regime parameters so that stakeholders, decision-makers, and dams managers may take efficient actions to mitigate or rehabilitate riparian ecosystems. In the present study, Hydrologic Alteration Indexes on Rivers (IAHRIS, for its acronym in Spanish) and the Mexican standard approach were considered to evaluate 1150 gauged catchments in Mexico and come up with an alteration baseline for 67.03% of the country surface. The comparison may assist stakeholders to propose potential changes in the Mexican standard approach. Results reveal that 232 analyzed catchments can be considered as non-altered according to IAHRIS. In stark contrast, there are 281 non-altered catchments in Mexico in agreement with the official standard approach. Altered catchments are mainly impacted by minimum flow metrics and connectivity discharge. Additionally, the correlation between alteration indexes and 5 socio-economic variables was checked to identify which variables may greatly impact hydrologic alteration evolution or mitigation. From the five selected variables, the Human Development Index is significatively correlated to extreme minimum metrics (p = 0.94) while the Gross Domestic Product to extreme maximum metrics (p = 0.90).

Predicting River Flow Using an AI-Based Sequential Adaptive Neuro-Fuzzy Inference System

Artificial intelligence (AI) techniques have been successfully adopted in predictive modeling to capture the nonlinearity of natural systems. The high seasonal variability of rivers in cold weather regions poses a challenge to river flow forecasting, which tends to be complex and data demanding. This study proposes a novel technique to forecast flows that use a single-input sequential adaptive neuro-fuzzy inference system (ANFIS) along the Athabasca River in Alberta, Canada. After estimating the optimal lead time between four hydrometric stations, gauging data measured near the source were used to predict river flow near the mouth, over approximately 1000 km. The performance of this technique was compared to nonsequential and multi-input ANFISs, which use gauging data measured at each of the four hydrometric stations. The results show that a sequential ANFIS can accurately predict river flow (r2 = 0.99, Nash–Sutcliffe = 0.98) with a longer lead time (6 days) by using a single input, compared to nonsequential and multi-input ANFIS (2 days). This method provides accurate predictions over large distances, allowing for flow forecasts over longer periods of time. Therefore, governmental agencies and community planners could utilize this technique to improve flood prevention and planning, operations, maintenance, and the administration of water resource systems.

Explore the relationship between fish community and environmental factors by machine learning techniques

In the face of multiple habitat alterations originating from both natural and anthropogenic factors, the fast-changing environments pose significant challenges for maintaining ecosystem integrity. Machine learning is a powerful tool for modeling complex non-linear systems through exploratory data analysis. This study aims at exploring a machine learning-based approach to relate environmental factors with fish community for achieving sustainable riverine ecosystem management. A large number of datasets upon a wide variety of eco-environmental variables including river flow, water quality, and species composition were collected at various monitoring stations along the Xindian River of Taiwan during 2005 and 2012. Then the complicated relationship and scientific essences of these heterogonous datasets are extracted using machine learning techniques to have a more holistic consideration in searching a guiding reference useful for maintaining river-ecosystem integrity. We evaluate and select critical environmental variables by the analysis of variance (ANOVA) and the Gamma test (GT), and then we apply the adaptive network-based fuzzy inference system (ANFIS) for an estimation of fish bio-diversity using the Shannon Index (SI). The results show that the correlation between model estimation and the biodiversity index is higher than 0.75. The GT results demonstrate that biochemical oxygen demand (BOD), water temperature, total phosphorus (TP), and nitrate-nitrogen (NO₃-N) are important variables for biodiversity modeling. The ANFIS results further indicate lower BOD, higher TP, and larger habitat (flow regimes) would generally provide a more suitable environment for the survival of fish species. The proposed methodology not only possesses a robust estimation capacity but also can explore the impacts of environmental variables on fish biodiversity. This study also demonstrates that machine learning is a promising avenue toward sustainable environmental management in river-ecosystem integrity.

Predicting impacts of future climate change and hydropower development towards habitats of native and non-native fishes

Climate change and hydropower development are two primary stressors affecting riverine ecosystems and both stressors facilitate invasions by non-native species. However, little study has focused on how habitats of native and non-native fishes may be affected by independent or combined impacts of such stressors. Here we used the Jinsha River as an example to predict habitat change and distributional shift of native and non-native fishes with species distribution models. The Jinsha River Basin has nearly 40 cascade dams constructed or planned and located in the Tibetan Plateau, which is sensitive to future climate change. Two climate change scenarios and future hydropower development were combined to produce five scenarios of future changes. Under the impacts of independent extreme climate change or hydropower development, non-native fishes showed greater habitat gain in total, while native fishes shifted their distribution into tributaries and higher elevations, and impacts were stronger in combined scenarios. Habitat overlap between the two groups also increased in future scenarios. Certain fish traits correlated with stressors in habitat change prediction. River basins with hydropower development were shown to face higher risk of non-native fishes invasion under future climate change. As the most biodiverse river basins globally are threatened by hydropower development, our results emphasize the importance of regulating non-native fish introduction in reservoirs. Our approaches are also applicable to other systems globally to better understand how hydropower development and climate change may increase invasion risk, and therefore help conserve native species effectively.

Integrating MAES implementation into protected area management under climate change: A fine-scale application in Greece

Increasing anthropogenic pressures often jeopardize ecosystem integrity and policy-relevant conservation management in protected areas. To harmonize nature conservation with human well-being, EU Biodiversity Strategy to 2020 suggests Mapping and Assessment of Ecosystems and their Services (MAES) as the key concept for environmental planning and management in EU Member States. Applying this procedure is challenging due to its data-demanding and multidisciplinary nature, resulting in the ecoystem services (ES) approach being scarcely used in protected areas management. Increased data availability under EU biodiversity-related inventories and monitoring projects, as well as theoretical and empirical research advances developed during the last decade, should be put into practice to guide Member States towards local management frameworks and scenario building under the ongoing changes in the EU socio-economic environment. This study aims at filling this gap by embodying into the MAES operational framework a scenario-based approach and demonstrates this in a challenging case study of a Natura 2000 site, Lake Stymfalia, in Greece. The present management strategy, an ecological-friendly management practice, a water-efficient management practice and a non-environmentally friendly option (e.g. ecosystem destruction) are examined for current and future water demand under current and future climatic scenarios. The proposed methodological framework for ES operationalization is based on the available data (derived by EU Directives and/or modelling), expert judgment and stakeholder involvement. Therefore, this work applies and tests the importance of the MAES approach as a management and coordination platform.

Changes in Water Level Regimes in China’s Two Largest Freshwater Lakes: Characterization and Implication

The complex water regimes and fragile ecological systems in Dongting Lake and Poyang Lake, located in the middle reach of the Yangtze River, have been significantly affected by regional climate change and anthropogenic activities. The hydrological data from the outlets of Dongting Lake (Chenglingji station) during 1955–2016 and Poyang Lake (Hukou station) during 1953–2014 were divided into two periods: the pre-impact period and the post-impact period. Four statistical tests were used to identify the change years: 1979 at Chenglingji and 2003 at Hukou. The indicators of hydrologic alteration and range of variability approach were used to assess alterations in water level regimes. Results show that the severely altered indicators were January water level at both lake outlets, and 1-, 3-, 7- and 30-day minimum water level at Chenglingji, with the degree of hydrological alteration being larger than 85%. The overall degrees of hydrological alteration at Chenglingji and Hukou were 52.6% and 38.2%, respectively, indicating that water level regimes experienced moderate alteration and low alteration or that ecosystems were at moderate risk and low risk, respectively. Changes in water level regimes were jointly affected by climate change and anthropogenic activities. Water level regimes at Dongting Lake outlet were mainly affected by increased rainfall and dam regulation. Decreased rainfall, dam regulation, and sediment erosion and deposition were the main impact factors of water level regimes at Poyang Lake outlet. These changes in water level regimes have greatly influenced both aquatic and terrestrial ecosystems, especially for fish and vegetation communities. This study is beneficial for water resource management and ecosystems protection under regional changes.

Using a hierarchical model framework to assess climate change and hydropower operation impacts on the habitat of an imperiled fish in the Jinsha River, China

Climate change and hydropower operations affect hydrological regimes at regional basin scales and impact hydrodynamics and habitat conditions for biota at the river reach scale. The present study proposes a hierarchical modeling framework for predicting and analyzing the impacts of climate change and hydropower on fish habitats. The approach couples multi-scale climate, hydrological, water temperature, hydrodynamic and habitat suitability models and was applied to a reach of the Jinsha River. Flow discharge and water temperature were predicted in the study area for a baseline scenario and three climate change scenarios, and each considered the presence and absence of impacts caused by hydropower operation. The impacts of flow discharge and water temperature variations on spawning and juvenile Coreius guichenoti, an imperiled warm-water fish in the Jinsha River Basin (JRB), were evaluated using a fuzzy logic-based habitat model. The results showed that habitat suitability and available usable area for the fish increased due to climate change, and water temperature rising was the main influencing factor. Water temperature decrease induced by hydropower operation in the spawning periods resulted in the reduction of available habitat area. However, climate change reduced the negative effects generated by hydropower operation, and the available habitat area for the fish would still be expected to increase under the combined impacts of climate change and hydropower operation in the future. It is predicted that water warming, as a result of climate change, is likely to eliminate the spawning postponement effect generated by hydropower operation on Coreius guichenoti as well as other warm-water fish species in the JRB. In contrast, water warming induced by climate change is likely to exacerbate the negative effects of hydropower operation on the spawning activity of cold-water fish species in the JRB. The present study provides a scheme to predict the impacts of climate change and hydropower on other organisms in river ecosystems. The results are beneficial for the development of long-term and adaptive conservation and restoration measures for aquatic ecosystems.

Delimitation of Agricultural Areas with Natural Constraints in Greece: Assessment of the Dryness Climatic Criterion Using Geostatistics

The Less Favored Areas (LFAs) scheme has existed in various forms since 1975 and it is a broad mechanism supporting rural development in agricultural areas with natural constraints (ANC). Within the programme period 2014–2020, the European Commission developed a common set of biophysical criteria (soil, climate, and terrain) to meet the requirement for a robust and harmonized approach of delimiting ANC throughout the EU Member States. Soil and terrain criteria can be derived directly from soil maps using geospatial analysis techniques based on the provided guidelines. However, the assessment of climatic criteria can be challenging especially in regions characterized by increased spatial variability and data scarcity. In this paper, the assessment of the dryness climatic criterion in a data-scarce region (Greece) as well as the challenges, limitations, and solutions are presented. Daily data-series from 140 meteorological stations for a 30-year reference period were analyzed and the spatial distribution of the precipitation and the potential evapotranspiration for each year were estimated in order to make the final assessment of the dryness criterion. Climate variability and the presence of trends were investigated as well. The obtained results indicated that most of the utilized agricultural area is affected by dryness due to a combination of low precipitation and high evapotranspiration rates. The extreme spatial variability especially in precipitation was also highlighted. An important temporal variability was observed as well, including indications of decreasing trends in precipitation and aridity index. Climate variability and possible trends should be investigated in more detail using longer time series in order to evaluate their impact in agricultural production.

Response of a multi-stressed Mediterranean river to future climate and socio-economic scenarios

Streams and rivers are among the most threatened ecosystems in Europe due to the combined effects of multiple pressures related to anthropogenic activities. Particularly in the Mediterranean region, changes in hydromorphology along with increased nutrient loadings are known to affect the ecological functions and ecosystem services of streams and rivers with the anticipated climate change being likely to further impair their functionality and structure. In this study, we investigated the combined effects of agricultural driven stressors on the ecology and delivered services of the Pinios river basin in Greece under three future world scenarios developed within the EU funded MARS project. Scenarios are based on combinations of Representative Concentration Pathways and Shared Socioeconomic Pathways and refer to early century (2030) and mid-century (2060) representing future climate worlds with particular socioeconomic characteristics. To assess the responses of ecological and ecosystem service indicators to the scenarios we first simulated hydrology and water quality in Pinios with a process-based model. Simulated abiotic stressor parameters (predictors) were linked to two biotic indicators, the macroinvertebrate indicators ASPT and EPT, with empirical modelling based on boosted regression trees and general linear models. Our results showed that the techno world scenario driven by fast economic growth and intensive exploitation of energy resources had the largest impact on both the abiotic status (nutrient loads and concentrations in water) and the biotic indicators. In contrast, the predicted changes under the other two future worlds, consensus and fragmented, were more diverse and were mostly dictated by the projected climate. This work showed that the future scenarios, especially the mid-century ones, had significant impact on both abiotic status and biotic responses underpinning the need for implementing catchment management practices able to mitigate the ecological threat on waters in the long-term.

Determination of environmental flows in rivers using an integrated hydrological-hydrodynamic-habitat modelling approach

We propose the novel integrated modelling procedure 3H-EMC for the determination of the environmental flow in rivers and streams; 3H-EMC combines Hydrological, Hydrodynamic and Habitat modelling with the use of the Environmental Management Classes (EMCs) that are defined by the Global Environmental Flow Calculator. We apply 3H-EMC in the Sperchios River in Central Greece, in which water abstractions for irrigation cause significant environmental impacts. Calculations of the hydrodynamic-habitat model, in which the large and the small chub are the main fish species, suggest discharge values that range from 1.0 m³/s to 4.0 m³/s. However, hydrological modelling indicates that it is practically difficult to achieve discharges that are higher than approximately 1.0-1.5 m³/s. Furthermore, legislation suggests significantly lower values (0.4-0.5 m³/s) that are unacceptable from the ecological point of view. This behaviour shows that a non-integrated approach, which is based only on hydrodynamic-habitat modelling does not necessarily result in realistic environmental flows, and thus an integrated approach is required. We propose the value of 1.0 m³/s as the "optimum" environmental flow for Sperchios River, because (a) it satisfies the habitat requirements, as expressed by the values of weighted useable area that are equal to 2180 and 1964 m² for the large and small chub, respectively, and correspond to 82 and 95% of their respective maximum values, (b) it is consistent with the requirements of Environmental Classes A and B, whose percentiles are higher than 75% for discharge (77.2%) and for habitat availability (>83.5% for the large chub and >85.0% for the small chub), (c) it is practically achievable from the hydrological point of view, and (d) it is higher than the value proposed by the Greek legislation. The proposed modelling approach can be applied to any river or stream using the same or similar modelling tools, which should be linked via suitable coupling algorithms.

Projected effects of Climate-change-induced flow alterations on stream macroinvertebrate abundances

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.

Structural and functional recovery of macroinvertebrate communities and leaf litter decomposition after a marked drought: Does vegetation type matter?

Climate change and anthropogenic disturbances are expected to lead to more intense and frequent droughts, with potentially severe effects on structure and function of perennial temperate streams. However, more information is required on whether streams flowing through basins already affected by exotic plantations will respond to droughts in the same way as streams under native forests. The recolonisation dynamics of benthic macroinvertebrate communities and leaf litter decomposition rates were examined in nine streams of oceanic-temperate climate that differed in catchment vegetation (three streams draining native deciduous forest, three in pine plantations and three in eucalypt plantations) after a marked drought. In each stream, five benthic samples were collected three times (ca. 1.5months between sampling dates) after flow recovery, and the taxonomic and functional trait compositions of the macroinvertebrate communities were analysed. The decomposition rate of Alnus glutinosa was measured in fine- and coarse-mesh litter bags. Benthic macroinvertebrate density, richness and diversity increased with time after flow recovery but only richness and diversity differed among stream types, with eucalypt streams showing the lowest values. Both the taxonomic and functional compositions of the macroinvertebrate community were dependent on vegetation type and time, with the differences among stream types diminishing over time. While leaf-litter decomposition rate did not depend on catchment vegetation after drought, detritivore activity was the lowest under eucalypt streams and it was positively correlated to benthic shredder density. Our results indicated that in these perennial temperate streams the catchment vegetation influenced the recovery of benthic macroinvertebrate communities after a period of drought, although the decomposition rate of leaf litter was not strongly affected. Greater understanding of the structural and functional responses of stream ecosystems to different stressors is required before the effects of expected more intense and frequent hydrological changes caused by climate change can be adequately forecast.

Comparative Assessment of Environmental Flow Estimation Methods in a Mediterranean Mountain River

The ecological integrity of rivers ultimately depends on flow regime. Flow degradation is especially prominent in Mediterranean systems and assessing environmental flows in modified rivers is difficult, especially in environments with poor hydrologic monitoring and data availability. In many Mediterranean countries, which are characterized by pronounced natural variability and low summer flows, water management actions usually focus on prescribing minimum acceptable flows estimated by hydrologic methods. In this study, a comparative assessment of environmental flow estimation methods is developed in a river with poorly monitored flows and limited understanding of past reference conditions. This assessment incorporates both a hydrologic and a fish habitat simulation effort that takes into consideration hydrologic seasonality in a Greek mountainous river. The results of this study indicate that especially in data scarce regions the utilization of biotic indicators through habitat models, may provide valuable information, beyond that achievable with hydrologic methods, for developing regional environmental flow criteria. Despite the widespread use of the method, challenges in transferability of fish habitat simulation provide undefined levels of uncertainty and may require the concurrent use of different assessment tools and site-specific study.

Drought and detritivores determine leaf litter decomposition in calcareous streams of the Ebro catchment (Spain)

Drought, an important environmental factor affecting the functioning of stream ecosystems, is likely to become more prevalent in the Mediterranean region as a consequence of climate change and enhanced water demand. Drought can have profound impacts on leaf litter decomposition, a key ecosystem process in headwater streams, but there is still limited information on its effects at the regional scale. We measured leaf litter decomposition across a gradient of aridity in the Ebro River basin. We deployed coarse- and fine-mesh bags with alder and oak leaves in 11 Mediterranean calcareous streams spanning a range of over 400km, and determined changes in discharge, water quality, leaf-associated macroinvertebrates, leaf quality and decomposition rates. The study streams were subject to different degrees of drought, specific discharge (Ls^-1km^-2) ranging from 0.62 to 9.99. One of the streams dried out during the experiment, another one reached residual flow, whereas the rest registered uninterrupted flow but with different degrees of flow variability. Decomposition rates differed among sites, being lowest in the 2 most water-stressed sites, but showed no general correlation with specific discharge. Microbial decomposition rates were not correlated with final nutrient content of litter nor to fungal biomass. Total decomposition rate of alder was positively correlated to the density and biomass of shredders; that of oak was not. Shredder density in alder bags showed a positive relationship with specific discharge during the decomposition experiment. Overall, the results point to a complex pattern of litter decomposition at the regional scale, as drought affects decomposition directly by emersion of bags and indirectly by affecting the functional composition and density of detritivores.

Assessment of the natural flow regime in a Mediterranean river impacted from irrigated agriculture

Over the last few decades, the natural flow regime of most rivers has been significantly altered influencing the ecological integrity and functioning of river ecosystems. Especially in the Mediterranean region, irrigated agriculture is considered one of the most important drivers of hydro-morphological modifications in river systems. In this study we employ the Indicators of Hydrologic Alteration (IHA) methodology for the Pinios River and its tributaries, located in a Mediterranean catchment in central Greece, with the purpose to assess the natural flow regime under a simulated no-agriculture scenario and compare with the current situation. The work is based on the use of the SWAT (Soil Water Assessment Tool) model for the simulation of long time series of daily stream flows, which were analyzed under the actual conditions (baseline), and the hypothetical scenario. The key characteristics of the flow regime projected under each model run were assessed through the implementation of the IHA methodology that utilizes a number of indicators to characterize the intra- and inter-annual variability in the hydrologic conditions. The results of this study revealed that without agricultural activities in the catchment, annual and monthly flows would increase, with significant alterations in the flow characteristics of the winter months, and much smaller in summer. However, the analysis showed that the frequency of droughts and low flow summer events would be smaller. The article provides a comprehensive and easy-to-implement methodology that can facilitate the impact assessment of agricultural human activities on river flow variability under the typical Mediterranean conditions, allowing experimentation on setting river flow thresholds required for a good ecological status within the context of the European Water Framework Directive.

Shifts in the suitable habitat available for brown trout (Salmo trutta L.) under short-term climate change scenarios

The impact of climate change on the habitat suitability for large brown trout (Salmo trutta L.) was studied in a segment of the Cabriel River (Iberian Peninsula). The future flow and water temperature patterns were simulated at a daily time step with M5 models' trees (NSE of 0.78 and 0.97 respectively) for two short-term scenarios (2011-2040) under the representative concentration pathways (RCP 4.5 and 8.5). An ensemble of five strongly regularized machine learning techniques (generalized additive models, multilayer perceptron ensembles, random forests, support vector machines and fuzzy rule base systems) was used to model the microhabitat suitability (depth, velocity and substrate) during summertime and to evaluate several flows simulated with River2D©. The simulated flow rate and water temperature were combined with the microhabitat assessment to infer bivariate habitat duration curves (BHDCs) under historical conditions and climate change scenarios using either the weighted usable area (WUA) or the Boolean-based suitable area (SA). The forecasts for both scenarios jointly predicted a significant reduction in the flow rate and an increase in water temperature (mean rate of change of ca. -25% and +4% respectively). The five techniques converged on the modelled suitability and habitat preferences; large brown trout selected relatively high flow velocity, large depth and coarse substrate. However, the model developed with support vector machines presented a significantly trimmed output range (max.: 0.38), and thus its predictions were banned from the WUA-based analyses. The BHDCs based on the WUA and the SA broadly matched, indicating an increase in the number of days with less suitable habitat available (WUA and SA) and/or with higher water temperature (trout will endure impoverished environmental conditions ca. 82% of the days). Finally, our results suggested the potential extirpation of the species from the study site during short time spans.