Average precipitation greatly decreased from the northwestern river basin districts to the southeastern ones, with great variation within each of the river basin districts. The use of non-conventional resources was still minor. Desalination plants were in Mediterranean river basin districts, such as C.M. Andaluzas, Segura, Júcar, and C.I. de Cataluña. Reuse of the treated water was broadly distributed and was in continuous growth, in all the river basin districts, but was still minor. The water demands highlighted the importance of agrarian use in most river basin districts: Miño-Sil (73.2%), Duero (91.1%), Tajo (71.1%), Guadiana (89.9%), Tinto-Odiel-Piedras (62.0%), Guadalquivir (88.9%), Guadalete-Barbate (70.0%), C. M. Andaluzas (70.9%), Segura (87.8%), Júcar (79.6%), and Ebro (92.2%).
4.1. Climate-Change Effects on Water Resources
As a result of the fourth report of the IPCC [35
] and on the basis of the models of climate change that were published for Spain, in the year 2012, the Public works research and experimentation center (Centro de Experimentación de Obras Públicas, CEDEX) published a series of reports on the evaluation of the effects of climatic change on the hydrological resources and water bodies, for all Spanish River Basin Districts [36
]. These works were developed from the regionalized climatic scenarios for Spain, within the framework of the IPCC’s fourth report [35
]. The emission scenarios were selected and transferred to all hydrological demarcation plans (SRES A2 y SRES B2) were a part of the set of greenhouse gas emission scenarios, established in the year 2000, in the special report on emission scenarios by the IPCC group (SRES A2: This scenario reflects the situation of non-adoption of measures to reduce emissions; SRES B2: This scenario incorporates reduction measures to alleviate the pernicious effects of climate change).
These reports conclude that climate change will have an impact on rising temperatures, a widespread decrease in rainfall and runoff, and an increase in rainfall irregularities. The consequences of these changes on water resources, according to these reports, will be: (1) Increased evapotranspiration and, therefore, a general increase in consumption and water demands (mainly plant and agricultural demand); (2) reduction of rainfall, runoff, and natural contributions will lead to a decrease in available water resources; (3) worsening of the ecological state of rivers (other types of bodies of water were not evaluated); and (4) increased pluviometry irregularity that would cause an increase in the uncertainty of water availability.
All of these consequences, obviously, negatively impact the vulnerability of the systems for coping with periods of drought in the future, which is exacerbated in the absence of adequate adaptation to the new scenario that climate change poses. In this sense, the consideration and application of climate change forecasts in the planning of water resources in Spain, has been insufficient, as shown in Table 2
. Mainly, the Spanish River Basin Districts introduce these considerations weakly and are limited to apply percentages of reduction contained in the Hydrologic Planning Instruction for calculating the resources available in scenarios 2027 and 2033.
Recently CEDEX [37
] has published an update on the climate change assessment of water resources and droughts in Spain. Although it has not yet taken the time to incorporate the new conclusions on the effects of climate change on water resources in the river basin district plans, it should be included in the new planning cycle (2021–2027). Unlike the document published in 2010 [36
], the new regionalized scenarios for Spain are based on the AR5 (Fifth Climate Change Assessment Report) [38
], which introduces updates to the General Circulation Models (GCM), as in the emission scenarios used. The GCM used in the AR5 are called. The General Circulation Coupled Atmosphere-Ocean Models (MGCAO) simulate the dynamics of the physical components of the climatic system (atmosphere, ocean, earth, and ice cap); and the most complete Terrestrial System Models (TSM), and include the representation of several biochemical cycles, such as those involved in the carbon, sulfur, and ozone cycles.
Additionally, the AR5 has defined four new emission scenarios, the so-called Representative Paths of Concentration (RCP), which replace the SRES used in previous reports (SRES 2 and SRES 4). News RCP used are RCP 2.6, RCP 4.5, RCP 6.0, and RCP 8.5. Each RCP is associated with a high spatial resolution database of pollutant emissions (classified by sectors), GHG emissions and concentrations, and soil uses up to the year 2100, based on a combination of models of different complexity of atmospheric chemistry and the carbon cycle (IPCC 2013).
In the Spanish case, the Meteorology State Agency (Agencia Estatal de Meteorología
, AEMET) has carried out a regionalization of the climatic scenarios of the RCP 4.5, 6.0, and 8.5, and the CEDEX has used RCP 4.5 (scenario of stabilization of the GHG emissions, where the maximum CO2
concentration in the atmosphere is estimated at 528 ppm) and RCP 8.5 (scenario with very high levels of GHG emissions, where the concentration of maximum atmospheric CO2
is estimated at 936 ppm) for the report on the impact of climate change on water resources and droughts in Spain. The conclusions of the report for the variables, which can determine the availability of water resources in the future, are presented in Table 3
Estimates in both scenarios show a widespread decrease in rainfall, soil moisture, aquifer recharge and runoff, and an increase in evapotranspiration, for the entire country, which would become more acute as the 21st century progresses. It is true that the RCP 8.5 scenario estimates are more pronounced. An increase in the potential evapotranspiration is also generally seen.
In general, it recognizes a reduction of water resources in the whole peninsula, more intense in the south and in the archipelagos, and a minor reduction in eastern parts of the Iberian Peninsula. This decrease in the availability of resources will result in an increase in the scarcity of water resources to meet demands [39
]. In addition, the same report predicts a change in the drought regime. Most climatic predictions show a future in which droughts would be more frequent and intense, blaming the progress of the 21st century for increasing exposure to these kinds of episodes in the future.
The hydrological plans of the different river basin district is to partially incorporate the forecasts of climate change in such a way that scenarios 2027 and 2033 include the decline in the availability of resources (but not the estimates of the increase in evapotranspiration), the consequent increase in demand, and the effects of climate change on the state of the water masses. The usual recurrence of droughts in Spain and the predicted increase in their frequency and intensity make it necessary to incorporate the period of drought’s pluviometry normality and a review of the availability of resources that takes into account the variability of drought periods, as a standard, and not as an exception, in order to make a resource allocation much more adjusted to the actual availability of the resources necessary.
4.2. Water-Stress Level for Different River Basin Districts
In Spain, it usually rains enough to meet demands. Furthermore, the country also has a great regulation capacity (56,000 hm3
). However, the mentioned rainfall variability (interannual, seasonal, and spatial) is combined with a growing demand of water for different purposes [39
]. In the Spanish River Basin Districts (2015–2021), the total demand of water amounts to 31,355.4 hm3
, of which 80.4% of which is agrarian, 15.6% urban, and 4.2% industrial demands [39
The level of pressure to which the water resources are subjected in the ordinary hydrologic planning determines the response of the system when a drought occurs and negatively impacts the sensitivity of the system. The greater the pressure on water resources the more difficult it will be to meet demands when the availability of resources decrease due to drought. The level of pressure on the water resources in a system of exploitation or river basin district, can be characterized by two variables—the stress to which the water resources are subjected and the state of the water bodies after various demands.
In Table 4
, a synthesis of natural contributions is presented (hm3
/year). Available resources (hm3
/year) were calculated as the natural conventional resource to which non-conventional (reuse and desalinization) was added, also subtracting the transferred flows to other basins and adding those received by transfers from other areas of planning and consumption demand (urban, agricultural, and industrial) (hm3
/year). The calculations were done on the official published data of the WEI.
Water Exploitation Index is a widely recognized indicator used to characterize the level of pressure on the water resources of certain territories or river basins [40
]. This indicator relates the total use of resources (consumptive and non-consumptive) to the total renewable resources, expressed as a percent. According to Eurostat, WEI values below 10% imply that the analyzed system is not subjected to any form of stress, if the value is between 10–20% it implies a low water-stress level. If the indicator exceeds 20% it is considered to have raised the alarm for water-stress levels, and if it exceeds 40% the system is in severe stress. Another very similar indicator is the WEI+ (which is an evolution of the WEI) and it relates the total amount of resources consumed (consumption with no returns) to the total amount of renewable resources.
Due to the variety of methodologies used in each river basin district to calculate these parameters, we have used two different methods of calculation. First, we used an adaptation of the WEI proposed by García and Martínez (2016) [41
]. This entails dividing the total consumption demands (excluding hydroelectric use) between the natural contributions, which results in the quantitative relationship between water availability and human pressure. In addition, the official results presented are the same as that published by CEDEX itself (2017), in which the WEI+ was calculated on the basis of the relationship between the demands of the available resource, which is also expressed as a percentage. The results obtained through the two methodologies (WEI+ and *WEI+) showed similar results for all river basin districts. The main difference lay in the Segura River Basin demarcation, due to the amount of water this area receives from the Tajo-Segura transfer which significantly increases the amount of resources available. For the rest of the demarcations both indexes (WEI+ and *WEI+) present similar values that can be used as a reference to determine the state of pressure on the water resources.
According to the data obtained, only four of the fifteen demarcations analyzed (Cantábrico Occidental, Cantábrico Oriental, Galicia Costa, and Miño-Sil) had levels of stress below 10% which shows that they had little to no water stress. Three demarcations (Duero, Tajo, and the internal basins of Catalonia) had values between 20% and 40%, presenting alarming levels of stress on their resources. The rest of the demarcations had very high values, well above 40%, which indicated severe stress. The average value for all fifteen demarcations was slightly above 31%. Although both values place the entire country in a water-stress alert level, the mean value for all demarcations was skewed by the extreme values of some of the demarcation’s data, which were not representative of the country. If the median value is used, where extreme values do not affect the average as much, a WEI value of 45.4% and a WEI+ value of 46.9% is achieved.
The results obtained show that many of the Spanish demarcations were subject to severe water-stress levels. In addition, the demarcations with higher rates of water stress were also those that had the greatest availability of resources (except Cantábrico Occidental, Miño-Sil, and Galicia Costa) indicating that in most cases it was not a water availability issue but that of excessive pressure on the existing resources.
The other indicator used to characterize the existing pressure on the hydrological resources was the state of the water bodies. Water bodies are a fundamental element which is articulated in the Water Framework Directive (WFD) and in the hydrologic planning. The purpose of the Directive is to reach a good status, for all water bodies, to ensure the adequate supply of surface and groundwater, and to require a sustainable, balanced, and equitable use of water, as stated in Article 1 of the WFD.
Different demands are assigned to the water bodies in order to meet the water use needs of the different sectors. Therefore, the state of the water masses is not merely a goal, but also a condition for adequate water supply to meet the demands. When a period of drought occurs, the qualitative and quantitative status of a water body can be affected and can limit the ability to satisfy demands, either by reducing the amount of available water or by worsening the quality of water. The state of water bodies affects the way in which the water body responds to the decreased precipitation. In Table 5
, data on the global state of surface water and groundwater bodies, for each of the Spanish River Basin Districts, are presented and analyzed.
For surface water bodies, 43.4% of the bodies of the water presented had a global status of “worse than good”, while 56.6% had a status of “good”. Duero (70.2% the bodies of water had a “worse than good” status), Guadiana (69.6%), Tinto-Odiel-Piedras (50%), Guadalete-Barbate (54.6%), and Jucar (63.3%) had the highest percentage of bodies of water that did not reach the “good” status; being always above 50%.
For groundwater, 41.4% of the water masses had a “bad” state. Guadiana (80%), Tinto-Odiel-Piedras (75%), Guadalete-Barbate (64.3%), Cuencas Mediterráneas Andaluzas (65.7%), Segura (73%), and Cuencas Internas de Cataluña (64.9%) had waterbody percentages that reached the “bad” global status of above 50%.
Of the 5582 bodies of water analyzed (above and below ground), 41.3% did not reach the “good” overall state. In seven of the fifteen river basin districts, more than 50% of the bodies of water did not reach a “good” overall status (Duero (66.5%), Guadiana (70.2%), Tinto-Odiel-Piedras (51.3%), Guadalete-Barbate (55.8%), Cuencas Mediterráneas Andaluzas (55.9%), Segura (55.9%), Júcar (50.2%), and Cuencas Internas de Cataluña (64.9%).
Both the amount of pressure on water resources and the global state of bodies of water showed a generalized situation of high pressure on the Spanish water resources of the different river basin districts, which increased the sensitivity to suffer impacts (economic, environmental, and social), before the onset of a drought.
4.3. Development and Implementation of Drought Planning
The main tool used to cope with droughts in the risk management paradigm are drought plans, as recognized by the major international agencies [42
]. The theoretical planning of these tools are based on two basic ideas. First, the probability of eliminating the risk does not exist, but can be minimized, and second, planning while anticipating the problem has many advantages: (1) It allows researchers to learn and analyze what causes systems to become vulnerable to periods of drought and how to fix the problem preemptively; (2) it prevents hasty decisions being made in response to the crisis. Therefore, the objective of the drought plans is to determine the arrival and departure of the different drought phases and the specific measures of action necessary for each social phase [11
]. Hence, the prevention and gradual adaptation to a drought as it progresses to reduce the economic, environmental, and social impacts.
In Spain, Article 27 of the National Hydrological Plan Act establishes the obligation to prepare special plans of action for alert situations and eventual droughts in all River Basin Districts (PES), and urban supply system emergency plans (PEM).
4.3.1. Special Action Plans during Conditions of Alert and Eventual Drought (PES)
PES are an important step forward in conceptual and operational terms, as it aims to evaluate drought, objectively, and to implement progressive measures with which to prevent droughts from becoming more severe [44
].These plans, which must be made by the watershed agencies in each of the river basin districts and must be coordinated with the hydrological demarcation plans, make up the system of indicators and thresholds used to identify the different states of drought (Normal, pre-alert, and emergency), as well as exploitation rules and the measures to be implemented concerning public ownership of water at each stage (Article 27.2. National Hydrological Plan Act).
In any case, the first steps of this new policy have suffered from a number of teething problems. (1) PEM due for 2005 were only published by the inter-regional basins in 2007, while the first-cycle hydrological plans (2009–2015) were published even later (some of them as much as six years late). These hydrological plans must be incorporated into the drought plans, but there is no guarantee that the targets and measures contemplated in both will be compatible. The late publication and inadequate updating of the PEM makes integrating current (but out-of-date) PES (2007) and second cycle hydrological planning (2015–2021), published in late 2015, with up-to-date information concerning resource inventories, demand, and, especially, ecological flows, very difficult. (2) The drought indicators in use are, in fact, indicators of scarcity. While indicators of scarcity may be useful in assessing and comparing supply and demand, they fall short of discriminating between ‘meteorological drought’ (caused by below-average rainfall) and water scarcity related to reservoir and aquifer levels, which depend, to a large extent, on the management model in place, and the usage of water before and after rainfall declined. As such, these plans are little more than contingency plans to address shortcomings in supply, but are largely unrelated to meteorological drought. The WFD permits the temporary deterioration of bodies of water, but only in unforeseeable and exceptional circumstances (Article 4.6. WFD). Adjusting the indicators to ensure that the reasons behind the deterioration of bodies of water are adequately accounted for, is essential for the correct implementation of the WFD.
In 2017, the Ministry of Agriculture, Fisheries, and Food (MAGRAMA) published technical guidelines concerning special drought plans and prolonged drought and scarcity indicators (TG), which established a number of rules for the updating of PES. Certain basin authorities have already published drafts of the updated PES. The revision of PES, which is currently under way, is an opportunity to continue advancing towards a drought-management model, based on prevention, mitigation, and progressive adaptation. We must take this opportunity to discriminate, at long last, between the prolonged meteorological droughts and socially constructed, management-induced scarcity. In addition, we must ensure that the various planning processes, for instance PES and PEM, are better coordinated in the future.
4.3.2. Emergency Plans (PEM) for Supply Systems That Serve Urban Agglomerations with a Population in Excess of 20,000 Inhabitants
These plans are only concerned with urban areas with a population in excess of 20,000 inhabitants, and are, therefore, the responsibility of the authorities in charge of overseeing the water supply. The aim of these PEM is to prevent drought from affecting the urban supply. However, although the deadline for the publication of PES was 2005, only a few have been published and their impact has been, therefore, very limited.
The publication of the new PES draft in December 2017 meant that progress could be assessed, with regard to PEM. These drafts identified two hundred and thirteen supply systems for urban areas, with over 20,000 inhabitants, which are, thus, required to provide a PEM. Only 8.5% of these supply systems have a PEM approved by the relevant PES (2007); 11.3% systems have already delivered their PEM, and this is currently being evaluated by the relevant basin authorities; 9.9% have a PEM in place, but the plans need to be revised and fitted to adapt the relevant PES, either because it was published before the PES and, in consequence, it does not follow the PES guidelines, or because, despite the PEM being published after the PES, the indicators used do not fit those used in the relevant PES. Most systems (70.4%) have not yet submitted their PEM to the relevant basin authority.