Drought, considered to be one of the most important natural risks in some parts of the world and one of the greatest threats for society today [1
], presents extensive negative impacts, which range from environmental to socio-economic aspects [4
]. In Europe, comparison between the 1976–1990 and 1991–2006 periods shows a duplication of both the area and the population concerned by this natural phenomenon [8
]. In this respect, it had already become apparent a decade ago that the number of people and regions affected by drought and water scarcity had increased by 20% between 1976 and 2006. The total cost associated with these episodes during those three decades amounted to 100 billion euros. For example, in the drought of 2003, one of the most intense, a third of the territory of the European Union and more than 100 million people were affected and its economic impact amounted to 13 billion euros [9
In 2017, the Centre for Research on the Epidemiology of Disasters [10
] published a report on the principal natural disasters that had occurred throughout the world during the first half of 2017. In relationship with economic damages, the report emphasizes that, of the ten most serious episodes, three correspond to droughts. The economic losses associated with this risk represented 38% of the total. In relationship with the population affected by natural hazards, droughts placed in first place. Of the ten most relevant episodes during the first half of 2017, eight were related to this risk, accounting for 66% of the population affected by these risks in the world (some 39.1 million people).
Drought has been considered an exceptional situation and the main instruments used to mitigate it have been reactive and emergency measures; that is, the construction of infrastructures to increase the supply of water resources and economic compensations for the damages and losses caused [11
]. These initiatives, according to Wilhite [12
], are included in what has been called the “crisis management focus”, which has been shown to be insufficient to alleviate the effects of drought for the following reasons: (1) it limits the solutions to technical aspects. Its design does not include the evaluation of alternatives or the stakeholders’ involvement; (2) it diverts attention to causes which provides that a decrease in precipitation generates shortages, and attributes their causality to the natural phenomenon without questioning the way in which the resource is managed and used; and (3) it produces a process of depoliticization that facilitates prioritization of technological solutions.
Subsequently, an alternative has been presented, the so-called “risk management focus”, described as measures of a proactive nature and aimed at prevention and mitigation of drought impacts [12
]. This measure focus on identifying where the vulnerability lies (sectors, regions, communities, or population groups) to implement measures for mitigation and adaptation to future droughts. Despite the advances deriving from this new focus, as Vargas and Paneque [13
] indicate, drought continues to be one of the least-understood natural risks. The intrinsic complexity of the meteorological phenomena that govern the patterns of appearance of dry periods is accompanied by a series of characteristics that differentiate it from other risks and which pose considerable difficulties for its management. In this respect, as pointed out by Del Moral et al. [14
], it is necessary to estimate and minimize its effects via ordinary water planning and coordination between the different sectorial policies (agricultural, spatial, and environmental) rather than having recourse to an exceptional route, such as drought orders. These hinder the application of the principles of prevention (anticipating the problems) and precaution, since they usually apply emergency procedures that do not facilitate the adoption of well-formulated and executed solutions. Furthermore, the drought risk is difficult to determine, since it depends not only on its duration, intensity, or geographical extension (variable of hazard), but also on the conditions of the society affected (vulnerability and exposure) [15
] and its capacity to adapt and to confront this natural phenomenon [13
]. As Vargas and Paneque [16
] indicate, droughts may (or may not) produce situations of lack of water supply. This will depend on the level of demand and on the characteristics of the management and exploitation systems and access to the availability of non-conventional resources, such as desalination [17
In Spain, during the second half of the twentieth century, the expansion of irrigated land, urban development, industrialization, the development of tourism activities, and hydroelectric power favored a sharp increase in demand for water, sometimes exceeding the natural supply of available resources [22
]. This increase was accompanied by actions (transfers, reservoirs, and groundwater harnessing, mainly) aimed at increasing supply, which enlarged the risk of hydrological drought [23
]. Thus, the lack of water infrastructure, the increase in consumption, and the precarious management of supply have extended their effects to regions theoretically well-endowed with resources, such as the Atlantic coast [24
]. As Del Moral et al. [14
] argue, unlike meteorological drought (which only takes into account precipitation in the affected area) hydrological drought is frequently the state brought about by a policy of continued increase in water supply.
The effects of climate change should also be added to these factors. In the Mediterranean Basin, not only is there an increase in average temperatures estimations, but also a reduction of precipitation or changes in the rainfall regime, which will intensify drought episodes [25
] and the tensions relating to the water availability [26
]. In this respect, the European Commission already considered in 2007 that the preparation of efficient drought risk management strategies should be considered a priority.
The solution to increase water volumes has been the incorporation of non-conventional resources (desalination and the reuse of treated water). Higher quality water (desalinated water) can be set aside for drinking water and that of lower quality (treated water) can be used for other activities that are less demanding, such as agriculture [27
]. Given the progress made in water treatment, water can now be created depending on quality needs, with water management policies that are based on the “fit for purpose” concept [28
]. Desalination has become a key water resource in arid and semi-arid areas [29
]. In the Mediterranean Basin, for example, this resource is already considered an ordinary supply source in some regions, and especially in many islands. In Israel, for example, it has become the main source for urban supply [30
]. Its use is also combined with inter-basin transfers, recycling, and diversification of fresh water away from agriculture [31
]. Australia is another country characterized by diversification of water sources in order to achieve self-sufficiency [32
], as is California (U.S.) [33
The starting hypothesis is that the resilience of south-eastern Spain (Segura River Basin; study area) has changed with the incorporation of non-conventional flows. According to Holling [34
], resilience determines the persistence of relationships within a system and is a measure of the ability of these systems to absorb changes of state variables, driving variables, and parameters, and still persist. In this definition, resilience is the property of the system and persistence or probability of extinction is the result. Corroboration of this affirmation is considerably important for various reasons. Firstly, because the risk of drought in this territory will become more intense and recurrent according to the climate change scenarios [35
]. In second place, because the study area is characterized by presenting water demands that exceed the supply. According to the Segura Basin Management Plan (2015–2021) [36
], it is estimated at 400 hm3
/year. And lastly, it is an area that since the late 1970s has depended on water transferred from the Tagus River Basin via the Tagus-Segura Aqueduct (TSA) (600 m3
/year). Its future functioning will be compromised by the approval of more conservative management rules, an increase in demand in the donor basin, and the uncertainty of the effects of climate change [22
]. The aims of this study are: (1) To analyze the main measures for management and planning implemented during recent decades in south-eastern Spain (Segura River Basin) to respond to drought situations, focusing on the role played by non-conventional water resources (desalination and treated water); and (2) to assess the level of resilience of this territory on the basis of the measures implemented, especially coinciding with the current drought of 2015–2018.
The structure of the paper is as follows. After the Introduction, which explains the problems and asserts the risks of drought at both an international and national level (Mediterranean region), the Methodology is described, together with consultation of the data. The Results are then presented, followed by the Discussions, which offers a debate regarding the strategic role that may be played by non-conventional water resources during drought situations, and lastly, the Conclusions.
Methodologically, various documentary sources have been consulted, reviewed, and analyzed in relationship with the current situation regarding non-conventional water resources in order to assess their relevance as a means of adaptation to drought in the study area (Segura River Basin) (Figure 1
). It is appropriate to indicate that, administratively, this area corresponds to a greater extent to the Region of Murcia and to a lesser extent to Castilla-La Mancha, the Valencian Community (province of Alicante), and Andalusia (province of Almeria). But it is in the provinces of Murcia and Alicante where demand is highest, due to the population supplied (2.5 million inhabitants, plus another million in the summer season as a result of residential tourism) and the irrigated land (147,276 ha).
First, the Segura Basin Management Plan (2015–2021) [36
] was consulted. Specifically: (1) Data referring to the water resources available and those demanded; (2) those relative to the reduction of supply due to the effects of climate change; and (3) figures regarding the capacity and use of reclaimed and desalinated water.
Second, data on re-used water have been analyzed, provided by various organizations: The Spanish National Statistics Institute (last data available at national level; 2014) [37
]; the water treatment companies (Entidad Pública de Saneamiento de Aguas Residuales—Public Entity of Wastewater Treatment of the Valencia Community—EPSAR) for the province of Alicante (2016) [38
]; and Entidad de Saneamiento y Depuración (Entity for Wastewater and Sewage—ESAMUR) for the Region of Murcia (2012) [39
]. Regarding data on desalination, information has been obtained from various sources: (1) Desalination plants managed by the Taibilla Canals Association (Mancomunidad de los Canales del Taibilla, MCT) (2003–2017) [40
] (Plants of San Pedro del Pinatar I and II and Alicante I and II); and (2) desalination plants managed by Aguas de las Cuencas Mediterráneas (Waters of the Mediterranean Basins-Acuamed) (Águilas, Valdelentisco, and Torrevieja plants) (2017) [41
Third, data and documents have been analyzed relating to water resources and supply sources in the study area provided by the main users: (1) Urban users (Taibilla Canals Association—Mancomunidad de los Canales del Taibilla, MCT) [40
]; and (2) agricultural users (Association of Tagus-Segura Aqueduct Irrigators—Sindicato de Regantes del Acueducto Tajo-Segura, SCRATS) [42
]. Regarding the MCT, this is the main public organization that supplies water for urban uses: 80 municipalities belonging to the provinces of Murcia, Alicante, and Albacete and an area of approximately twelve thousand square kilometers.
In relationship with the SCRATS, this entity supplies water to 80,000 irrigators and a total gross area (that is, with allocation and the right to irrigate with water originating from the river Tagus) of 147,276 hectares, which enables 104,000 direct jobs. By regions, Murcia irrigates 85,397 ha with water from the TSA (57.97% and with an allocation of 260 hm3
/year), Alicante 58,878 ha (39.98% and an allocation of 125 hm3
/year), and Almeria 3000 ha (2.03% and an allocation of 15 hm3
]. Lastly, transfers made by the TSA (1979–2017) have been consulted, given the relevance of these resources in the Segura Basin and their effects (reduction of the volumes transferred) in drought episodes.
The Segura Basin is a less vulnerable region to drought than a few decades ago. The measures implemented in recent decades (use of non-conventional water resources, changes of water paradigm, measures to manage the demand, and the implementation of drought plans) in south-eastern Spain to mitigate the effects of drought has increased its resilience to this hazard. One of the conclusions drawn in this research is the importance and role of non-conventional water resources. Especially, during drought situations and their extreme importance in achieving territories that are more resilient to climate change, not only during dry periods but also as an available resource to take into account during normal rainfall years. In periods of normal rainfall, demand management (reduction of urban and agricultural consumption) has also been shown as a measure aimed at adapting to the drought of this territory.
Desalination has not only become a strategic water resource of vital importance during drought situations, but it is increasingly configured as an ordinary source for urban supply in coastal areas of the European Mediterranean [21
]. During the current drought situation (2015–2018), all the desalination plants of the A.G.U.A. program in the Segura Basin have become operational, with the exception of Torrevieja, which can only produce half of its capacity due to lack of power supply (some 40 hm3
/year). The plants of the MCT, during the period that the TSA was closed, supplied around 60–70% of the resources demanded in the coastal and pre-coastal sector of the provinces of Alicante and Murcia. Thanks to this, on the coast of south-eastern Spain, there have been practically no restrictions in urban supply during this period, unlike the drought of the 1990s [46
]. One of the reasons for them in this last period was due to the non-existence of the non-conventional water resources (desalination and treated water) [45
]. It must be also noted that its promotion and generalization as a substitute resource for TSA transfers will be increased in the future. This is because more and more, the contributions from aforementioned transfer will be reduced by episodes of drought and the new conservative exploitation rules for the ceding basin.
The use of re-used water for agricultural and urban uses has allowed, on the one hand, has reduced the pressure on fresh water, and on the other, encouraged a more sustainable use of water resources by incorporating them into the water cycle. According to the Segura Basin Management Plan (2015–2021), urban wastewater treatment plants treated 140.1 hm3, of which 78.2 hm3 was reused directly (55.82%) and practically all the rest indirectly (water discharged into the river Segura which is subsequently reused).
Despite being the most region arid in Spain and with a natural scarcity of water, the endeavors undertaken in this territory make it one of the best adapted to water scarcity. Even with the increase in resilience, it is necessary to be critical and change the perception of the exclusive dependence on TSA transfers in the south-east of Spain and think about a new approach and integrate all available water resources. The TSA should be considered as another source and it should be taken into account that it will be an unavailable resource coinciding with years of drought in the headwaters of the Tagus. Therefore, all available resources should be integrated into a water mix (own resources, surface, underground, water from the TSA—when it will possible, desalination, and treated water) and should be developed and given more importance in water policies from the perspective of management of the demand and a more efficient use of resources.