Assessing Water Shortage through a Balance Model among Transfers, Groundwater, Desalination, Wastewater Reuse, and Water Demands (SE Spain)

Assessing current and future available resources to supply urban water demands using a high-resolution SWAT model coupled with recurrent neural networks and validated through the SIMPA model in karstic Mediterranean environments

Hydrological simulation in karstic areas is a hard task due to the intrinsic intricacy of these environments and the common lack of data related to their geometry. Hydrological dynamics of karstic sites in Mediterranean semiarid regions are difficult to be modelled mathematically owing to the existence of short wet episodes and long dry periods. In this paper, the suitability of an open-source SWAT method was checked to estimate the comportment of a karstic catchment in a Mediterranean semiarid domain (southeast of Spain), which wet and dry periods were evaluated using box-whisker plots and self-developed wavelet test. A novel expression of the Nash-Sutcliffe index for arid areas (ANSE) was considered through the calibration and validation of SWAT. Both steps were completed with 20- and 10-year discharge records of stream (1996-2015 to calibrate the model as this period depicts minimum gaps and 1985-1995 to validate it). Further, SWAT assessments were made with records of groundwater discharge and relating SWAT outputs with the SIMPA method, the Spain's national hydrological tool. These methods, along with recurrent neural network algorithms, were utilised to examine current and predicted water resources available to supply urban demands considering also groundwater abstractions from aquifers and the related exploitation index. According to the results, SWAT achieved a "very good" statistical performance (with ANSE of 0.96 and 0.78 in calibration and validation). Spatial distributions of the main hydrological processes, as surface runoff, evapotranspiration and aquifer recharge, were studied with SWAT and SIMPA obtaining similar results over the period with registers (1980-2016). During this period, the decreasing trend of rainfalls, characterised by short wet periods and long dry periods, has generated a progressive reduction of groundwater recharge. According to algorithms prediction (until 2050), this declining trend will continue reducing groundwater available to meet urban demands and increasing the exploitation index of aquifers. These results offer valuable information to authorities for assessing water accessibility and to provide water demands in karstic areas.

Optimal Water Resources Allocation in the Yinma River Basin in Jilin Province, China, Using Fuzzy Programming

Being one of the most important sources of water in the Jilin Province in China, the Yinma River Basin (YRB) is facing problems of water scarcity in low economic areas and low utilization in richer areas mainly caused by the irrational allocation of water, excessive pursuit of economic benefits, and neglect of environmental problems. Restricting watershed development involves potential decision-making risks. Some scholars have used the interval two-stage stochastic planning method to adjust water resource allocation in the Drinking Horse River Basin, but the method uses historical statistics for projection and does not take into account the ambiguity and uncertainty in real planning situations. Therefore, this study addresses the problems prevalent in the allocation of water resources in the YRB through optimization using stochastic programming methods, interval and two-stage, and introduces the fuzzy mathematical programming method, with the aim of coordinating the water balance of various water-consuming sectors in the YRB, so as to reconfigure the water allocation. The goal is to solve the existing problems of irrational water allocation, reduce system risks posed by excessive economic development, mitigate water shortages in the water-consuming sectors, and alleviate potential decision-making risks and vague uncertainties associated with the allocation of water resources. Additionally, optimization of the pollution-holding capacity improvement project was carried out. The interval fuzzy two-stage model simulation developed in this study shows that the distribution of water across the different administrative regions can be reduced by up to 30% compared with the original model, effectively reducing the problem of water wastage. Post-optimization, the impact of water shortage in the water resources allocation scheme is alleviated to a significant degree, and there is no water shortage in some areas. At the same time, the eco-environmental sector has gradually taken the leading role in the distribution of water reuse among the different water-consuming sectors. The pollution-holding capacity has been enhanced, and the discharge and river entry chemical oxygen demand (COD) and ammonia nitrogen, two typical pollutants, have been reduced. The membership interval in the interval fuzzy two-stage model reflects the relationship between the possible level of the target value and the risk level. This study provides a guideline for decision makers for balancing the relationship between benefits and risks and proposes a planning scheme that is more conducive to the development of the river basin.

Extending Natural Limits to Address Water Scarcity? The Role of Non-Conventional Water Fluxes in Climate Change Adaptation Capacity: A Review

Water consumption continues to grow globally, and it is estimated that more than 160% of the total global water volume will be needed to satisfy the water requirements in ten years. In this context, non-conventional water resources are being considered to overcome water scarcity and reduce water conflicts between regions and sectors. A bibliometric analysis and literature review of 81 papers published between 2000 and 2020 focused on south-east Spain were conducted. The aim was to examine and re-think the benefits and concerns, and the inter-connections, of using reclaimed and desalinated water for agricultural and urban-tourist uses to address water scarcity and climate change impacts. Results highlight that: (1) water use, cost, quality, management, and perception are the main topics debated by both reclaimed and desalinated water users; (2) water governance schemes could be improved by including local stakeholders and water users in decision-making; and (3) rainwater is not recognized as a complementary option to increase water supply in semi-arid regions. Furthermore, the strengths–weaknesses–opportunities–threats (SWOT) analysis identifies complementary concerns such as acceptability and investment in reclaimed water, regulation (cost recovery principle), and environmental impacts of desalinated water.

Identifying Problems in Watering Ponds with Different Purposes

The main goal of this study was to identify the problems that are putting the viability of watering ponds at risk. For doing that, we have analyzed five different study cases: (I) livestock consumption, Mediterranean climate (rangelands of SW Spain), (II) multifunctional ponds (Arroyo de la Luz, Spain), (III) ecotourism (Valdepajares de Tajo, Spain), (IV) crop irrigation and fish farming, semi-arid climate (the wilaya of Ouargla, Algeria), and (V) livestock consumption, humid subtropical climate (Prudentópolis, Brazil). The identification of problems was made through surveys, personal interviews, local knowledge and literature review as well as through the analysis of water quality parameters such as the concentration of phosphates and fecal coliforms in some ponds. We have identified problems of water shortage (ca. 50% of rangeland farmers), pollution induced by agriculture (maximum values of phosphates = 1.33 mg L−1) and livestock farming (maximum value of fecal coliforms ≈ 7000 cfu mL−1), low potability for human consumption (score: 2.8/7.0), invasive species such as Azolla filiculoides (10 out of 17 watering ponds), high water temperature for aquaculture in summer (Algeria) and the increase of turbidity in nearby water courses due to the actions of free-fattening pigs (Brazil), among many other problems. We conclude an extra effort by stakeholders is still needed in order to agree mitigation strategies.

Legal Analysis and Case Study on the Choice between Setting Environmental Flows by Using Reclaimed Water in Non-Permanent Rivers and the Sustainable Management of Groundwater in Southeast Spain

This article studies the interaction between two environmental objectives actively pursued in water governance. On the one hand, the convenience of establishing or raising a minimum circulating flow in surface water bodies so to improve their quantitative and qualitative status. On the other hand, the need to carry out an intelligent management of aquifers avoiding their overexploitation. In the case study, the proposal consisting of increasing the minimum flow rate on a non-permanent river by means of discharging reclaimed water is studied. Such strategy jeopardizes the recovery of a number of overexploited aquifers since reclaimed water is currently being used for farming under the condition to proportionally reduce groundwater withdrawals. The aim is to discuss whether it is reasonable and rational to ensure continuous flows in water courses which do not have that pattern according to their natural dynamics to the detriment of other environmental or socioeconomic goals. In order to help decision makers to make a right choice, a set of criteria based on legal principles is proposed. According to the principles of minimum intervention, rationality and reasonableness, proportionality, and water economy, it is concluded that the use of reclaimed water to set higher environmental flows in discontinuous and ephemeral streams should only have a minor role in water policies, especially whether it may jeopardize other critical environmental goals.

Climate change impact on karstic aquifer hydrodynamics in southern Europe semi-arid region using the KAGIS model

Nowadays, there are many urban settlements in arid and semiarid areas supplied by groundwater from adjacent small aquifers. Climate projections with expected decreases in averages precipitation values jointly with increases in the frequency of heavy rainfall events does not show a clear pattern to how water resources in karstic aquifers are going to evolve. This paper, focused in the province of Alicante (Southeast of Spain), assesses the behaviour of a small karstic aquifer, the Mela aquifer, whose resources supply urban water consumption for close municipalities. We assess the hydrogeological response of the aquifer, through the KAGIS black-box GIS-based model, for the present climate conditions and for the long period analysing the four scenarios provided by the International Panel of Climate Change. Main results prove that, if we do not diminish the greenhouse gas emissions, the climate change impact on the hydrological response of the study aquifer shows a decrease in the flow rate from its unique spring and will be non-existent during the summer months. So, it will be necessary to design supply strategies for these municipalities and to carry out them, meeting budget restrictions and avoiding potential water shortages.

Wastewater Treatment and Water Reuse in Spain. Current Situation and Perspectives

The issues of wastewater treatment and the reuse of water are of great importance, especially in areas where the shortage of conventional resources is a structural problem, as it is in the case of Spain. Wastewater reuse is a valid mechanism to avoid problems derived from droughts and water scarcity. It allows access to water resources in areas with water restrictions and to prevent futures scenarios, due to it being expected that water consumption will double by 2050 over the world. Thus, the likelihood that this unconventional, strategic resource would become scarce is unquestionable, particularly in cases where water planning and exploitation systems prioritize the preservation, protection, and improvement of water quality, as well as the sustainable and efficient use of natural resources. This paper shows how wastewater treatment and reuse are linked, as the reuse of wastewater is associated with a previous regeneration, and both of them are essential tools for maximizing environmental outcomes, as called for in the European Union Directives.

Rainwater Harvesting for Agricultural Irrigation: An Analysis of Global Research

Within a context of scarce water resources for agriculture, rainwater harvesting constitutes a promising alternative that has been studied by different disciplines in recent years. This article analyses the dynamics of global research on rainwater harvesting for agricultural irrigation over the last two decades. To do this, qualitative systematic analysis and quantitative bibliometric analysis have been carried out. The results reveal that this line of research is becoming increasingly important within research on irrigation. Environmental sciences and agricultural and biological sciences are the most relevant subject areas. Agricultural Water Management, Physics and Chemistry of the Earth, and Irrigation and Drainage are the journals that have published the most articles on the subject. India, China, the United States (USA), South Africa, and the Netherlands are the countries that lead this line of research. Although significant progress has been made in this subject area, it is necessary to increase the number of studies on the capacity of rainwater harvesting systems to cover irrigation needs in different farming contexts, the factors that determine their adoption by farmers, the economic and financial feasibility of their implementation, and their contribution to mitigating global climate change.