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Surface water (SW) quality is particularly vulnerable to increased concentrations of nutrients, and this issue may be exacerbated by climate change. Knowledge of the effects of temperature and rainfall on SW quality is required to take the necessary measures to achieve good SW status in the future. To address this, the aims of this study were threefold: (1) to assess how a changing climate may alter the nitrate, ammonium, phosphorus and biological oxygen demand status (BOD5) of SW; (2) assess the relationship between water quality and flow; and (3) simulate diffuse and point source pollution reduction scenarios in the Júcar River Basin District in the Mediterranean region. A regionalised long-term climate scenario was used following one Representative Concentration Pathway (RCP8.5) with the data incorporated into the coupling of hydrological and water quality models. According to these climate change scenarios, SW with poor nitrate, ammonium, phosphorus and BOD5 status are expected to increase in the future by factors of 1.3, 1.9, 4 and 4, respectively. Furthermore, median ammonium and phosphorus concentration may be doubled in months with low flows. Additional measures are required to maintain current status in the water bodies, and it is necessary to reduce at least 25% of diffuse nitrate pollution, and 50% of point loads of ammonium, phosphorus, and BOD5.

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Highly regulated basins have traditionally required management practices to mitigate the negative environmental impacts and ensure human well-being. This paper proposes and assesses environmental and water supply deficit indicators to assist in the management of environmental flows (e-flows). For that, a water allocation model is applied, and hydrological alteration, habitat alteration and water supply indicators are quantified, normalized and integrated into a general basin management indicator. This basin management indicator is analyzed for four management approaches and seven e-flow scenarios in the Júcar River Basin (eastern Spain). Hydrological alteration indicators show a less pronounced alteration in the river sections located upstream of the basin while a higher alteration in the downstream sections. As for the habitat indicators, they experience an improvement compared to the natural regime. Based on the values of the basin management indicator, the best e-flow scenario to adopt in the Júcar River Basin is selected. The indicators proposed in this work are useful for supporting decision-making regarding the planning and management of e-flows in regulated river basins worldwide.

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This paper presents a methodology to assess the effects of management strategies of environmental flows on the hydrological alteration of river basins on a daily scale. It comprises the collection and analysis of data, the implementation and calibration of a water allocation model; the computation of the natural flow regime; and the estimation, normalization, and aggregation of hydrological alteration indicators to obtain a global indicator of the hydrological alteration. The methodology was applied to a case study in the Iberian Peninsula: The Orbigo River basin, which belongs to the Duero River basin district. For that, three management scenarios were defined: the current scenario, a scenario without any environmental flow and the scenario with the environmental flows initially projected for the period 2022-2027. These scenarios were modelled with the SIMGES water allocation model, which is calibrated in the study site, and the hydrological alterations in four river stretches with different locations and characteristics were assessed. The implications of each environmental flow scenario on the demand reliabilities were also analysed. The global indicator of hydrological alteration obtained in the projected scenario was greater (better) than those of the other two scenarios, but the reliabilities of the water demands were worse. The methodology proposed in this work can be helpful to design environmental flow regimes considering both the effects on the hydrological alteration and the implication on the water demand reliabilities.

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Freshwater ecosystems and water uses may be jeopardized by the degradation of water quality. The Water Framework Directive of the European Union (EU) sets environmental objectives for water bodies but foresees the establishment of exemptions under some circumstances. The criteria used to justify these exemptions, however, are not fully developed, leaving their application open to some arbitrariness. Our study explores the relations between the magnitude of pressures affecting continental surface water bodies and the declared exemptions on the permitted concentration of nitrogen. It identifies different approaches to declare exemptions to nitrogen environmental objectives across six EU Member States and discusses the underlying criteria. A better understanding of the pressures-impact-measures/exemptions relation helps compare water policy decisions across different regions subject to the same legal obligations and set priorities for mitigation measures.

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This study focuses on a novel type of methodology which connects Pan-European data to the local scale in the field of water resources management. This methodology is proposed to improve and facilitate the decision making within the planning and management of water resources, taking into account climate change and its expected impacts. Our main point of interest is focused on the assessment of the predictability of extreme events and their possible effects, specifically droughts and water scarcity. Consequently, the Júcar River Basin was selected as the case study, due to the ongoing water scarcity problems and the last drought episodes suffered in the Mediterranean region. In order to study these possible impacts, we developed a modeling chain divided into four steps, they are: i) data collection, ii) analysis of available data, iii) models calibration and iv) climate impact analysis. Over previous steps, we used climate data from 15 different regional climate models (RCMs) belonging to the three different Representative Concentration Pathways (RCPs) coming from a hydrological model across all of Europe called E-HYPE. The data were bias corrected and used to obtain statistical results of the availability of water resources for the future (horizon 2039) and in form of indicators. This was performed through a hydrological (EVALHID), stochastic (MASHWIN) and risk management (SIMRISK) models, all of which were specifically calibrated for this basin. The results show that the availability of water resources is much more enthusiastic than in the current situation, indicating the possibility that climate change, which was predicted to occur in the future has already happened in the Júcar River Basin. It seems that the so called "Effect 80", an important decrease in water resources for the last three decades, is not well contemplated in the initial data.

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One of the major difficulties in water planning is to determine the water availability in a water resource system in order to distribute water sustainably. In this paper, we analyze the key issues for determining the exploitable water resources as an indicator of water availability in a Mediterranean river basin. Historically, these territories are characterized by heavily regulated water resources and the extensive use of unconventional resources (desalination and wastewater reuse); hence, emulating the hydrological cycle is not enough. This analysis considers the Jucar River Basin as a case study. We have analyzed the different possible combinations between the streamflow time series, the length of the simulation period and the reliability criteria. As expected, the results show a wide dispersion, proving the great influence of the reliability criteria used for the quantification and localization of the exploitable water resources in the system. Therefore, it is considered risky to provide a single value to represent the water availability in the Jucar water resource system. In this sense, it is necessary that policymakers and stakeholders make a decision about the methodology used to determine the exploitable water resources in a river basin.

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The primary effects of droughts on river basins include both depleted quantity and quality of the available water resources, which can render water resources useless for human needs and simultaneously damage the environment. Isolated water quality analyses limit the action measures that can be proposed. Thus, an integrated evaluation of water management and quality is warranted. In this study, a methodology consisting of two coordinated models is used to combine aspects of water resource allocation and water quality assessment. Water management addresses water allocation issues by considering the storage, transport and consumption elements. Moreover, the water quality model generates time series of concentrations for several pollutants according to the water quality of the runoff and the demand discharges. These two modules are part of the AQUATOOL decision support system shell for water resource management. This tool facilitates the analysis of the effects of water management and quality alternatives and scenarios on the relevant variables in a river basin. This paper illustrates the development of an integrated model for the Llobregat River Basin. The analysis examines the drought from 2004 to 2008, which is an example of a period when the water system was quantitative and qualitatively stressed. The performed simulations encompass a wide variety of water management and water quality measures; the results provide data for making informed decisions. Moreover, the results demonstrated the importance of combining these measures depending on the evolution of a drought event and the state of the water resources system.

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