*3.2. The Water Balance in the Segura Basin: Supply and Demand in Vega Baja*

According to the Hydrological Plan of the Segura Basin (2015–2021), the total available resources of the basin (including the TTS) amounted to 1511hm3/year, and the total demand of the basin reached a volume of 1841 hm3/year. Given that the demand is higher than the available resources, the water deficit calculated for the whole of the Segura basin for this time horizon was 330 hm3/year [26].

Meanwhile, the recent Hydrological Plan of the Segura Basin (2022–2027) indicates that the total available resources in the basin (including the TTS) amount to 1571 hm3/year, which implies an increase in water resources in the basin. The total demand of the basin, meanwhile, amounts to a volume of 1831 hm3/year, representing a decrease in demand with respect to the previous time horizon, which is justified by the increase in water resources from non-conventional sources. This is whythe deficit has reduced to 260 hm3/year (Table 5) [27].

Considering the scenarios contemplated for 2027 and 2039 in the PHCS (2022–2027), two different trends may be identified: the first is the continued increase in water resources using non-conventional sources, such as those obtained through wastewater treatment and desalination in the Segura basin for 2027 and 2039. The second trend is related to the Segura basin's own water resources, such as surface and groundwater, which are set to decrease in terms of total annual volume. Furthermore, the plan considers that less sea discharges will take place in 2027 and 2039, which suggests an advance in the use and management of water.

A rising trend can be observed in the urban demand in the Segura basin. This coincides with the increase in agricultural demand for the 2027 and 2039 horizons [27]. This

constitutes a serious problem for agriculture, given that the Water Law 29–1985 and the subsequent Law of the National Hydrological Plan 2001 and Law 11/2005, which modifies the previously mentioned law, indicate urban supply as the priority use. This implies that in situations of extreme atmospheric events (droughts), priority is given to urban supply above other uses (ecological, irrigation and agricultural uses, industrial, etc.). Therefore, in the case of need, water will be extracted from the water allocations assigned to irrigation and agricultural users, thereby aggravating the consequences for irrigated crops.


**Table 5.** Segura River basin water balance (2022–2027).

Source: Hydrological Plan for the Segura River Basin (2022–2027).

With respect to the urban demand of the basin, the calculation of urban demand conducted by the CHS in the district of Vega Baja del Segura was performed. In 2021, urban demand was recorded at 39.2 hm3/year, and it is estimated that by 2039 it will have increased to 43.5 hm3/year [27]. It is interesting to note that the urban demand corresponding to the district of Vega Baja only represents 16% of the total demand of the Segura basin.

It is more interesting to analyse the agricultural demand of the district of Vega Baja del Segura, according to the data included in the PHCS. To achieve this, the gross or usable agricultural land and the net areas or those cultivated by UDAs (Units of Agricultural Demand) corresponding to the district of Vega Baja del Segura were chosen (Table 6).

As we can observe in Table 5, the PHCS shows that there is a gross or usable agricultural area of 65,411 hectares, of which 47,636 hectares are cultivated, representing 72.8% [27]. In the afore-mentioned plan, the total gross and net demands per crop and the total demand for per UDA are reported.

Table 5 shows the UDAs that depend on the waters of the Tajo–Segura Transfer are 52, 53, 56 and 72. This gives a total of 27,837hectares and an annual water demand of 117.9 hm3/year, while the UDAs that depend on available basin resources (46, 48, 51 and 55) add up to a total of 19,799 hectares and an annual water demand of 76,5 hm3/year. These data show that the UDAs that were rain-fed crops and were transformed into irrigated crops (new irrigation), because of the Tajo–Segura Transfer project, are the areas with the highest water demand and, consequently, the causes of the water deficit in the region of Bajo Segura.


**Table 6.** Area (gross and net) and demand (gross and net) by UDAs belonging to the region of Bajo Segura (Alicante).

Source: PHCS (2022–2027).

It is evident that climate change has a significant impact on water, which obliges the organisations of the basin to take it into account in hydrological planning. In this respect, the CHS establishes three future periods of 30 years, called impact periods (IP). These impact periods are IP1 (2010–2040), IP2 (2040–2070) and IP3 (2070–2100), reflecting the impact in the short, medium, and long term, in accordance with the medium (RCP 4.5) and high (RCP 8.5) climate scenarios (Table 7) [27].

**Table 7.** Effect of climate change with respect to an unaffected situation on hydrological variables in the DHS.


Source: PHCS (2022–2027).

In fact, the short-, medium- and long-term impacts of climate change related to water resources reveal a negative scenario for the Segura basin. As we can observe in Table 6, there will be a reduction in rainfall of between 8% and 14% in the Segura basin by the

end of the century. The potential and real evapotranspiration translate into negative effects; the humidity of the soil will also decrease; the aquifer recharge will face serious problems, oscillating between 20% and 36%; and finally, the surface runoff will decrease sharply throughout the whole of the Segura basin, with values fluctuating between 20% and 38% [27].The reason for using the RCP 8.5 scenario, which is characteristic of an extreme scenario of high emissions, is justified because the trend in emissions is increasing annually, the effect of climate change on the reduction inwater resources is notorious and, finally, because it justifies the proposal put forward in this research to carry out sustainable water planning.

#### *3.3. The Water Balance in the District of Vega Baja del Segura and the TTS*

Obtaining data on water resources (supply) in the region of Vega Baja del Segura has been a complex task. This is because there is no previous study of the water balance in this region. The data found are only represented in two scales: river basin scale or provincial scale (+140 municipalities, Alicante).

For this reason, the data that represent the water balance of the region of Bajo Segura are adjusted to its political limit composed of the 27 municipalities that make up it.In this sense, the data have been found in different bibliographies of official bodies such as the Segura River basin or the Diputación de Alicante, among others. All these data have been adjusted for the regional scale of work (Table 8).


**Table 8.** Water balance 2021 in the region of Vega Baja del Segura (Alicante).

Source: own elaboration based on PHCS (2022–2027), SCRATS (2020), EPSAR, ACUAMED, Generalitat Valenciana and Diputación de Alicante data.

The estimated deficit in the district of Vega Baja del Segura (Alicante) is 31.4 hm3/year. It should be noted that urban demand is completely guaranteed by the water resources from the River Taibilla, the TTS and the desalinated water used by the Mancomunidad de los Canales del Taibilla, which supply the municipalities of Vega Baja del Segura. Meanwhile, environmental demand is also guaranteed by the circulating waters of the river Segura and the returns to the system, which are used as ecological flows in the final section of the river Segura. The other demands (industrial, golf, etc.) are covered using water purified with a tertiary or advanced treatment. The problem of the deficit resides in agricultural demand, particularly in the so-called new irrigated lands, because the waters from the transfer are insufficient to supply the existing demand (Table 9).


**Table 9.** Estimated situation for future scenarios in the Vega Baja of Segura River (2030 and 2050).

\* Desalination: by 2030 the Torrevieja desalination plant will be expanded to 120 hm3/year, of which 80 hm3/year will be for agricultural use and 40 for urban use. By the year 2050, it is estimated that the production capacity will be 160 hm3/year, of which 120 hm3/year will be used for irrigation and the remaining 40 hm3/year for urban use. Source: own elaboration based on the scenarios proposed in the Segura River basin and the medium climate scenario RCP 4.5.

Of the 194.4 hm3/year of agricultural demand, according to the PHCS (2022–2027), a total of 160.8 hm3/year correspond to UDAs 52, 53, 56 and 72, which coincide with the sectors of the new irrigated land (former rain-fed land transformed into irrigated land); hence, there is high demand for water for two reasons: (a) the lands were originally dry and modern irrigation systems allow irrigated crops to be grown on them, and (b) the farms or plots are large with areas similar to those of latifundios (large estates).Therefore, a large amount of water is necessary to maintain their productivity and enable these areas to continue to produce irrigated crops (Table 10).

**Table 10.** Agricultural demand that takes advantage of the waters of the TTS in the Vega Baja del Segura.


Source: PHCS (2022–2027). Own elaboration.

In this respect, the Confederación Hidrográfica del Segura provided a series of data referring to the volume supplied of the transfer water to the 29 irrigation communities in the water year 2019/2020 (Table 11). This table reflects two relevant aspects: the concessional volume and consumption. The concessional volume refers to the amount of water assigned to each of the irrigation communities that are beneficiaries of the transfer water, corresponding to the theoretical values in the Preliminary Project of the Transfer, given that the total sum of the concessional volumes assigned to each irrigation community amounts to 123 hm3/year, 30% of which is allocated to the province of Alicante. It would be very difficult to achieve these theoretical amounts in the current climate and water context and considering the effects of climate change.


**Table 11.** Volume of water supplied by the water transfer to the CC.RR. of Alicante in the hydrological year 2019–2020.

Source: DHS (2020).

It is interesting to know the consumption per irrigation community, given that, if the value of consumption of each irrigation community has allowed sufficient irrigation for the crops to grow correctly and produce yields that are profitable for the farmer, this implies that the net agricultural demand of the beneficiaries of the TTS water fluctuates between the consumption values of 2020, that is, around 44 hm3/year (Table 11).

To corroborate this point, the data regarding the irrigated area of the district of Vega Baja del Segura provided by the Valencian Institute of Statistics (IVE) of the Regional Department of Sustainable Economy, Productive Sectors, Trade and Employment were consulted. These data reveal that there are variations in the size of the cultivated area in accordance with the droughts occurring and the availability of water resources. In this respect, in the years 2014–2016 (years of drought in the Segura Basin), there was an increase in the irrigated area, with an area of 16,399 hectares recorded in 2014 and 16,955 hectares in 2016. In the following two years of drought (2017–2018), the irrigated area decreased to values fluctuating between 16,500 and 15,500 hectares. Finally, it should be noted that in 2019, the cultivated area increased again to 16,321 hectares, a value close to that of 2020.

From the data provided by the IVE, it may be concluded that the municipalities with irrigated crops dependent on the TTS waters (new irrigated land) reduced their cultivated area in drought situations, as in the case of the municipalities of Orihuela, Albatera, Benferri, Pilar de la Horadada or San Miguel de Salinas, among others. Meanwhile, the irrigated crops that depend on the water resources from the Segura basin (Segura River) increase or maintain the same areas of irrigated crops in drought situations, even in the years of most severe rainfall and hydrological drought in the basin, as in the case of the years 2012, 2015 and 2018.

The loss of irrigated area dependent on the TTS water resources could have been even greater in the years 2015–2016 and 2017–2018 (drought in the Tajo, Júcar and Segura basins, among others), if the desalination plant of Torrevieja had not started operations as a strategic source to support the TTS in this type of situation [5].

Meanwhile, the data provided on the ARGOS Information Portal of the Regional Government of Valencia allows the addition of a series of socio-economic indicators that enable the relationship existing between economic development (agriculture) and the greater or lesser availability of water to be evaluated (Table 12).


**Table 12.** Socio-economic indicators in the Vega Baja del Segura in relation to the greater or lesser availability of water resources.

\* N/D: non data. Source: Valencian Cartographic Institute (ICV) (IVE), ARGOS and ACUAMED.

Thus, with respect to the average budget per inhabitant, a gradual increase from the year 2011 to 2019 may be observed. It continued to rise until 2021, reaching a value of EUR 1026.35/inhabitant.

Regarding the recruitment recorded in agriculture, in the year 2013–2014 an exponential increase in percentage terms can be observed, reaching a figure of 30.68%. This value decreased in the following year due to the severe drought (21.83%) and continued to decrease until 2018. From 2019, a growing trend began in the percentage of recruitment recorded in agriculture, reaching a value of 35.01% in 2021.

On the other hand, registered unemployment in agriculture displays different behaviour. From 2007 to 2016, unemployment in agriculture gradually increased. The highest values correspond to the drought years of 2015 and 2016, reaching 6.16% and 6.34%, respectively. From 2017 until the present day, the number of unemployed in agriculture has decreased to a level of 4.59 in the year 2020.

These indicators become more significant when they are examined in relation to the greater or lesser availability of water from both the TTS and desalination.

In March 2015, a drought situation was declared in the Segura basin, for which 12 exceptional measures were implemented for the management of water resources and EUR 30 million of extraordinary credit was assigned. In September of the same year, the drought continued, and the drought declaration was extended until September 2016. In addition to the measures already implemented, further action was taken with respect to the control of the continental waters. In October 2015, for the first time in Spanish history and in the Segura basin, among the new measures announced by the Ministry was the reduction in the price of desalinated water produced by the Torrevieja plant to 0.30 EUR/m3, with the authorisation of the production of 30 hm3/year and a subsidy of EUR six million to reduce the cost of production [29].

This highlights that, thanks to the production of desalinated water in the years 2015 and 2016, the area of irrigated crops in the district of Vega Baja del Segura remained the same. This is also visible in a similar value maintained of total agricultural income in the Region of Valencia.

In March 2018, Law 1/2018 of 6 March was passed, referring to the adoption of urgent measures to mitigate the effects generated by the drought in certain hydrographic basins. Additionally, the Revised Text of the Water Law, approved by Royal Legislative Decree 1/2001 of 20 July was modified, in response to the continued drought situation in a large part of Spain. This explains the decrease in the cultivated area in the years 2017, 2018 and 2019 in the district of Vega Baja del Segura, together with the reduction in agricultural income. Another problem that explains this worsened situation is that, from the year 2016–2017, the price of desalinated water increased to 0.60–0.80 EUR/m3. Farmers could not afford this price and opted to not cultivate or even abandon their irrigated land due to the absence of a guarantee of water resources.

However, in the water years 2017–2018, when there was a drought in the headwaters of the Tagus, the Torrevieja desalination plant reduced the price of its desalinated water (for the second time) to 0.30 EUR/m<sup>3</sup> for irrigators. This cost was farbelow that of production costs [5]. This coincided with the months of an absence of transferable resources or "no transfer", which obliged the desalination plant of Torrevieja to produce desalinated water at almost maximum capacity in 2019 [29,30]. The effects for the cultivated land and socioeconomic aspects were positive, thanks to desalination.

#### **4. Discussion**

The results reveal a series of problems in hydrological planning in Spain which directly affect the district of Vega Baja del Segura, in relation to the Tagus–Segura Transfer.

The analysis shows that the volumes of water available in the sub-basin of the Upper Tagus are not the same as those of fifty years ago, given that the average and maximum rainfall have reduced, the surface runoff has decreased and the volumes of water independently stored in the Entrepeñas and Buendía reservoirs have decreased sharply. This behaviour has also been observed in the joint water resources of Entrepeñas–Buendía since the beginning of operations of the TTS.

The reduction in rainfall recorded in the last period of climate analysis (1980–2018 series) is 15% with respect to the 1940–1979series and is consistent with what the CEDEX points out in its report on the impact of climate change on water resources in Spain [8] and with what Marcos and Pulido point out [31]. A decrease in winter and spring rainfall is also observed, which are the most effective for hydrological planning purposes (urban tourist and agricultural demands in summer) and a slight increase in autumn rainfall, in line with what has been pointed out by various authors [32–35] for the eastern sector of the Iberian Peninsula. Thus, the monthly distribution of precipitation in the headwaters of the Tagus tends to be "Mediterranean", with a more prominent participation of autumn rains.

The climate trends and their effects related to water resources in the Tagus basin (Upper Tagus) with respect to rainfall, surface runoff and the volume of water stored in reservoirs reveal a progressive reduction in available water resources. Taking into account the climate change scenarios (RCP 4.5 and RCP 8.5) and even after undertaking adaptation tasks, the Tagus basin is experiencing serious problems, which are being demonstrated and tested with scientific data.

As mentioned above, the Mediterranean region is the planetary zone where the effects of climate change will be most devastating [1]. In this sense, there are numerous scientific publications that have analysed this issue for the Mediterranean region. These studies show that, although the reduction in precipitation is not linear, but rather amplified (due to the increase in extreme weather events), two types of behaviours have been observed in the Mediterranean region. The first of these is obviously the reduction in average precipitation and the form of rainfall [11]. Greater amounts than historical records can now fall in a very short time. The second is that rainfall tends to concentrate on the Mediterranean coast and not in inland areas, where the headwaters of Spain's main rivers (such as the Tagus and Segura Rivers) are located [33–37]. If there is no rainfall in the headwaters of these rivers, there will hardly be any water resources in the basin and, consequently, no transfer from one basin to another will be possible. Therefore, it is considered that the TTS and the current hydraulic planning is unsustainable in the context of climate change.

The problems of the Upper Tagus directly affect the hydrological planning of the Segura basin, through the Tagus–Segura Transfer. One of the problems identified in the period of operation of the TTS (1979–2021), except for one year, is that the theoretical volumes assigned in the Preliminary Project of the Tagus–Segura Transfer have not been achieved, not even under the initial operating regulations. In fact, with respect to the demand and available water resources in the Segura basin thanks to the transfer, the Segura basin has never reached more than 2000 hm3/year as an available resource, even with the TTS, wastewater treatment and desalination. Meanwhile, demand has increased exponentially.

This is mainly due to the problems in the headwaters experienced in the Tagus basin because of climate change. The figure that demonstrates this aspect is the average volume of water transferred from the origin (208 hm3) and received in the destination (182 hm3), indicated by the CHS for the period contemplated [27]. Furthermore, the data of the SCRATS (Central Irrigation Syndicate of the Tagus–Segura Aqueduct) reveal that, of the 400 hm3/year assigned to irrigation in south-east Spain (theoretical), the average volume of the transfer for the period indicated is 195.6 hm3, that is, less than half of the assigned amount. Of the 400 hm3/year (theoretical), 30% corresponds to the province of Alicante, which is 120–125 hm3/year (theoretical). However, the reality is very different. Taking the data of the CHS into account, and particularly that of the SCRATS, the average volume of water received in the province of Alicante from the TTS is 61.1 hm3 in the period of operation (1979–2021). This implies that the province of Alicante receives half of the theoretical amount of water assigned to it.

This raises the following questions: Why has no reassessment or review been made of the operating calculations of the TTS in over 50 years? Why is planning undertaken with values that do not currently exist, nor will exist in the future? Why do the farmers denounce and call for volumes of water that they will never receive? The answer is clear: they are being deceived because they have been given no explanation about the current situation of the hydrographic basins because of climate change.

Therefore, the TTS displays a series of significant weaknesses subject to the variations in climate, and the territories which are supplied with its water resources must begin to adopt measures that do not directly depend on it (self-sufficiency). To obtain a greater volume of water, desalination and wastewater treatment are being used to contribute to the supply, enabling the deficit of the basin to be reduced to some extent.

However, the trends in urban and agricultural demand are growing, with the latter having the highest demand. It should be remembered that in the case of drought or a shortage of urban water supply, the water used to supply the urban nuclei will be drawn from other uses, such as ecological flows or those used for agriculture. Therefore, agriculture is losing water resources, and in the medium to long term, if measures are not taken to correct these problems, it will be seriously affected.

In this respect, and as a proposal for an empirical and demonstrated adaptation, the new irrigated lands (dependent on the TTS) enter a situation of pre-alert of drought much before the traditional irrigated lands. This was evident in the drought of 2015, after the passing of RD 356/2015 of 8 May, declaring the situation of drought in the territorial region of the Confederación Hidrográfica del Segura with the adoption of exceptional measures for the management of resources, due to the reduction in the interannual contributions (rainfall) in the headwaters of the Segura and Tagus basins and its successive extensions (RD 335/2016). In other words, the resources of the Segura basin can supply the traditional irrigated lands in situations of extreme drought, although not the crops dependent on external resources. This should constitute an incentive for changing the way hydrological planning is conducted in the Segura Basin, the Vega Baja district and in the rest of Spain.

With respect to the Alicante district of Vega Baja del Segura, the deficit existing is due to agricultural demand: principally, the irrigation communities that depend on the water resources of the transfer. This is because after the TTS project was approved, the construction of the transfer took 10 years until it began operation. During this period, there was much speculation in Vega Baja del Segura regarding the water that would be received, based on the afore-mentioned theoretical volumes. This speculation translated into the transformation of rain-fed crop land into irrigated land using groundwater. Therefore, the real use of the TTS has not increased the irrigated areas, but has maintained, as far as possible, all the transformed areas since then.

The current status of the non-conventional sources allows them to considerably reduce the deficit existing in Vega Baja del Segura, although this does not mean that there is no longer a deficit. If the desalination plant of Torrevieja operated at its maximum capacity (80 hm3/year), with the support of the treated wastewater (24–25 hm3/year), the deficit would be reduced to 10.5 hm3/year. The deficit would be resolved with the extension of the maximum production capacity of the Torrevieja desalination plant from 80 to 120, and subsequently to 160 hm3/year. This proposal is contemplated in the PHCS (2022–2027). In parallel, there would be an increase in the volume of reusable treated wastewater, which would complement the desalinated water. These two sources would become the principal water sources of the district of Vega Baja del Segura. The role of the TTS, therefore, would be a secondary or complementary source to these resources, when needed.

However, this increase in production should be accompanied by mechanisms imposed by the government based on Law 7/2021 of 2 May regarding climate change and energy transition, as a framework within which to reduce the cost of production of desalinated water, based on energy subsidies. In this way, the farmers would be provided with water for irrigation at a price of 0.20–0.30 EUR/m3, as in the case of the two occasions when the TTS failed during situations of extreme drought.

Taking all these issues into account, Spain needs to review and reconsider the current hydrological policy. To do this, first, it should begin by reviewing the values of the Preliminary Project of the TTS and adjust them to the volumes of water currently available. Furthermore, the water contributions assigned to each irrigation community dependent on the water from the TTS should be reviewed, given that they do not reflect the current situation. This analysis will reveal the available water resources. Second, after determining the situation of the water resources related to the TTS, it would be appropriate to increase the maximum capacity of the Torrevieja desalination plant (ACUAMED) in order to obtain larger volumes of water resources and maintain the plant in full operation as well as obtaining a price of desalinated water that is affordable for farmers. Third, agricultural demand should be reduced using new irrigation systems (drip system), a switch to irrigated crops that require less water or a radical change from irrigated crops to rain-fed crops and, as a more extreme measure, the reduction incultivable areas.

The new hydrological policy in Spain should be constructed on sustainability, climate change scenarios, hydrologic planning and on measures of adapting to climate change in a horizon of 100 years.

The *new sustainable hydrological planning* should be based on scenarios of climate change elaborated by the IPCC in its reports and on its regional effects. Sustainable planning means that, despite the existing resources, this exercise should be contextualised within the worst climate scenario possible, that is, in RCP 8.5 scenarios. Planning a climate and water resources situation based on the RCP 8.5 severity will enable a management of water resources able to guarantee the resource for the rest of the twenty-first century in Spain. If the reality is very different to that contemplated in the plan (due to a limitation of greenhouse gases, the implementation of measures to adapt to extreme atmospheric events and the respect and fulfilment of all the treaties and agreements in terms of reducing emissions), there will be a surplus and more water will be available for the assigned uses (urban supply, ecological flows, irrigation and agriculture, industry, leisure, tourism, etc.).On the contrary, if the scenarios contemplated in the RCP 8.5 are fulfilled, a prior adaptation to this situation will have already been contemplated and planned. Furthermore, the adoption of this approach would enable measures of adaptation to be developed over the years.

This new planning proposal will significantly slow down the environmental deterioration and socio-economic losses. If these aspects are not considered from today, the consequences will be much more severe in the medium and long term, and losses running to millions of euros will be incurred. It would be particularly severe for those crops dependent on the TTS. The implementation of hasty and drastic measures as the RCP 8.5 climate scenario approaches will lead to greater economic investments with dubious profitability. Furthermore, this new policy should be flexible and open to modifications which enable adaptations and adjustments to be made in accordance with the climate situation and the future scenarios contemplated.

The new planning and management scenario proposed in this paper is in line with the proposal in the mentioned Law 7/2021 on climate change in Spain, which advocates the incorporation of the effects of climate change into hydrological planning (art.19) to increase the resilience of the different uses of water. In particular, agricultural uses must adapt the demands to the expected resources to minimise the expected impact on future climate scenarios. The proposal for sustainable hydraulic planning in our study area is in correspondence with various authors in Spain who advocate a reduction in agricultural irrigated surfaces compared to the increase contemplated in various current hydrological demarcation plans (Guadalquivir, Guadiana, Tajo), or the maintenance of existing ones that are not sustainable, in present day and in climate change scenarios (Segura, Júcar) [36–38].

Moreover, the new sustainable hydraulic plan should focus on the management of the demand for water, with a commitment to non-conventional sources, desalination and wastewater treatment, with the afore-mentioned determinants (increase in capacity, reduction inthe production costs of desalinated water, mechanisms to reduce the energy and production costs of desalination, applying tertiary treatment to purified water so they may be reused for agricultural and other uses). After managing the resources of non-conventional sources, the water resources of the hydrographic basins should then be included (surface, groundwater, returns to the system, sea discharges, etc.). Next, the external water resources from other basins should be incorporated, such as those from the Tagus–Segura Aqueduct, as a strategic or complementary source which, when necessary, can transport water to satisfy the demands. Furthermore, it is also necessary to calculate the water needs per crop in order to determine the amount of water that is required to produce substantial yields of the crop and its fruit, administrating the necessary volume of water.

Another aspect that the new plan should contemplate isadaptation measures through water use agreements, such as those in Marina Baja (Alicante), where the irrigators concede clean water for urban supply while the regenerated water is used for irrigation in agriculture. To achieve this, it is preferable to establish an agreement between the interested parties (farmer, water company and the EDAR, among others).

After planning all these factors, it is necessary to supply all of the demands existing in the basin and territory as far as possible. Most likely, in the deficit basins which have transformed areas of rain-fed land into irrigated land (new irrigated land dependent on the TTS), different alternatives will have to be sought to satisfy their demand: desalinated water, treated wastewater, new irrigation systems, changing to soils and crops that require less water, or, in the most extreme case, reducing the crop areas in order to bring down demand.

The proposal presented in this study adapts to the objectives established by the Spanish government for the year 2050 which seek to promote the development of alternative sources of supply (reuse and desalination based on renewable energy), reduce the water lost in the sanitation and supply network, increase the quality of the water, "renewable water" and moderate consumption, among other actions.

The energy consumption of these facilities is currently around 3 Kw/h for each m3 of water produced (generally less than 4 in new facilities including auxiliary systems and other pumping) and has been reduced from values of over 20 Kw/h/m3 in the 1960s to current values [39,40].

Values of more than 20 Kw/h/m3 in the 1960s to have lowered to current values [39,40] thanks to improvements in the chemistry and configuration of the membranes and in the systems for recovering residual energy from the brine.

Energy consumption is the largest cost of desalinated water production, so its reduction is the key factor in reducing the price of desalinated water. The implementation in Spain of the National Integrated Energy and Climate Plan (2021–2030) and the EU legislative package "Fitfor 55" responds to the European Commission's recent commitment to reduce net greenhouse gas emissions by at least 55% by 2030.

In this context, projects are being developed for the implementation of solar farms to supply desalination facilities on the Spanish mainland and in the Canary Islands. In particular, the Torrevieja desalination plant, a key element in the supply of desalinated water, is developing a project to install an electrical substation, powered by solar energy, with the aim of obtaining self-consumption of energy. At present, the desalination plant's energy consumption is estimated at 264 GWh, which would increase to 400 GWh with the expansion of its desalination capacity to 120 hm3/year (from the current 80 hm3/year).

As mentioned above, the production capacity of the Torrevieja desalination plant is currently 80 hm3/year, where 40 isfor urban supply and another 40 for irrigation in the Segura River basin. However, the CHS plans to increase this to 120 in the current Hydrological Basin Plan (2022–2027). According to information provided by ACUAMED, the current specific consumption value of the Torrevieja plant varies between 3.25 and 3.65 kWh/m3, depending on the delivery point and the required water quality. It is capable of producing 1 hm3 per day (24 h), obtaining water with a conductivity of 200 μS, i.e., with a quality identical to that of mineral water and, therefore, water that can be used for irrigation. The economic cost of desalination for the years 2019, 2020 and 2021, and the resulting average tariff over the last years, is approximately 0.45 EUR/m<sup>3</sup> (water delivered).

Finally, they are rigorously monitoring the marine ecosystem impact caused by the discharge of brine or brine overflow. In this case, they ensure that they have zero environmental impact, as before dumping the brine they mix it with seawater and dump it in small quantities and in different areas to avoid causing damage to the marine environment. The Torrevieja desalination plant has eight sensors that monitor the salinity level, which have never once detected an environmental problem.

To achieve these water-related objectives for the year 2050, among the several actions proposed, the sixth addresses the need to "*adjust the management of water resources, preparing the system that will prevail in a future with a lower availability of water*" [41]. Therefore, "*a comprehensive water management strategy must be designed that promotes reuse and the desalination of water until its price is competitive, that is, similar to the price of water from traditional sources; improve the efficiency of the systems of urban supply, agricultural irrigation and the treatment of drinking water and wastewater, through the modernisation of infrastructures and the introduction of new technologies; reorder the agricultural and crop uses, acting on the prevailing concessional regime, prioritising sustainable and socially fair agriculture; increase the resilience of farms to extreme atmospheric events and the effects of climate change, through the transformation of crops and production systems, improve training in agricultural management and create adequate financial and governance mechanisms; and, finally, implement an ambitious strategy for restoring the rivers,*

*aquifers and other continental aquatic systems, while strengthening the river reserves and other protected spaces*" [41].

In short, the objectives established for Spain in 2050 are aligned with the proposal of the new hydraulic planning proposed in this research.

#### **5. Conclusions**

The climate and water situation in Spain and its respective hydrographic basins, particularly the Tagus and Segura basins, is not the same as it was 50 years ago, when the volumes of water to transfer via the Tagus–Segura Transfer were planned.

The Tagus basin has suffered a significant reduction in rainfall, surface runoff and volumes of reservoir-stored water in the sub-basin of the Upper Tagus. This is the starting point of the Tagus–Segura Transfer, and the reduction in water resources (surpluses) available in the Tagus basin has been modified by the effects of climate change. This has given rise to a serious problem, given that there will be less and less resources available to transfer. Therefore, the scenario of the Tagus basin will be to plan its own resources in order to supply the needs of its own basin, without taking into account the Segura basin, which is dependent on the waters of the TTS.

This implies that the Segura basin and the irrigated lands of south-east Spain will receive a lower volume of water from the transfer than theycurrently receive, given that the surplus resources of the Tagus basin are subject to variations in climate, rendering the transfer an infrastructure vulnerable to the effects of climate change. This is why the Segura basin should begin to make a firm commitment to using non-conventional sources, such as treated wastewater and desalinated water, the latter being the most important for the self-sufficiency of the basin, focusing on three fundamental aspects: (a) increasing the production capacity, (b) reducing the cost of the desalinated water supplied to the farmers (0.20–0.30 EUR/m3) and (c) reducing the environmental impacts (brine).

Furthermore, the farmers in south-east Spain, particularly those of the new irrigated lands dependent on the TTS, should know that they have been deceived with the promise of water resources assigned through the water contributions for each irrigation community, when these volumes were calculated more than 50 years ago when the climate reality was completely different. Furthermore, these volumes are theoretical and have never been fulfilled, at least in the province of Alicante. The undersupply of the TTS is not due to a failure to transfer the resources that should be transferred, but because there are not enough resources in the headwaters of the Tagus that can be transferred to fulfil the theoretical volumes.

Therefore, in response to the questions posed at the beginning of this article, it is clear that the Tagus–Segura Transfer is not the only solution for the water future of the district of Vega Baja del Segura. There are other alternative sources, such as treated wastewater and desalinated water, which can increase the volume of available resources to supply the urban and agricultural demands. However, it should be noted that, with the current maximum capacity for producing desalinated water in the district (80 hm3/year), the demand in Vega Baja cannot be satisfied. Therefore, it is necessary to extend the desalination plant of Torrevieja, increasing the production capacity to 120 hm3/year and complemented by the regenerated volumes of water. In this respect, it is necessary to extend the treatment plants of the district of Vega Baja del Segura with tertiary or advanced treatment, given that most of them only perform secondary treatment and the resulting water cannot be applied directly to the crops.

Finally, Spain should be more ambitious in terms of hydrological planning. It is incomprehensible that the plan that is in force with respect to the TTS is based on the theoretical volumes of a Preliminary Project when the climate situation was very different to that of the present day. No attempt has been made to reconsider the operating water volumes for the current scenario taking into account the effects of climate change.

For this reason, to correct the lack of a coherent and rational water plan that contemplates the climate reality and effects of future climate change, this study proposes a new sustainable hydraulic plan.

This new sustainable plan requires a profound restructuring of hydrologic planning, based on the worst climate scenario (RCP 8.5), enabling a plan to be elaborated with a long-term horizon (until the end of the century) and adapted to climate change. This scenario will lead to significant restrictions with respect to the current water allocations, whereby the assigned volumes of water will be initially reduced or eliminated. The positive side of this plan is that if the reality in terms of climate evolves over the years into a scenario with less emissions and a better adaptation and management of water, the volumes of water assigned to each use may be increased. This is the main reason why the principal sources in the sustainable hydraulic plan are treated and desalinated water, with the aforementioned improvements, as these resources do not depend on climate variations. Then, the basin resources will be included. As observed in the severe droughts occurring in Spain, the basin resources, and, therefore, the traditional irrigated lands that use this water, are more resilient and are adapted to extreme atmospheric conditions, giving them a clear advantage for the effects of climate change. Subsequently, the external water resources will be included, which, depending on the climate evolution over the coming years, will be based on the transfer or not of resources from the Tagus basin to the Segura basin. Therefore, in this proposal, instead of playing a principal role, the TTS is used as a strategic-secondary source to support the principal sources in the proposed plan. Moreover, the uses, crops, areas cultivated and water allocations will have to be reordered in order to reduce demand and, therefore, the deficit existing in the Segura basin in Vega Baja.

The new sustainable hydraulic plan is committed to the self-sufficiency of the territory and only in case of need would it request external resources. However, for a territory to be resilient to the future effects of climate change, it is necessary to start acting now with respect to the afore-mentioned aspects to minimise the socio-economic losses (job positions, crops, desertification, land, cultivated areas, significant economic losses in terms of production and agricultural income, among many others). All of this is possible through a logical plan and coherent actions. A failure to take such measures would result in consequences that will be catastrophic for south-east Spain and, particularly, for the farmers and their way of life. This proposal establishes the fundamental pillars for a long-term national strategy for Spain in the year 2050.

**Author Contributions:** Formal analysis, investigation, resources, data curation, writing, A.O.C.; formal analysis, investigation, resources, data curation, writing, J.O.C.; formal analysis, data curation, supervision, writing, C.J.B.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Data Availability Statement:** The data can be found in the documents referenced in this article. Likewise, the authors offer to provide any data requested by other researchers or interested parties.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

