Economic Valuation of Ancestral Artificial Aquifer Recharge Systems in High Mountain Environments of Sierra Nevada, Spain

Abstract

The study applies a cost–benefit analysis approach to assess the ecosystem services provided by ancestral systems of artificial recharge of high mountain aquifers, the “acequias de careo” (careo channels), in the Bérchules River basin, located in the Sierra Nevada, Spain. The methodology is structured in three main phases: (i) the definition of scenarios and system boundaries; (ii) the selection of ecological, social, and economic indicators; and (iii) the monetary valuation of benefits in comparison with operation and maintenance costs. The findings indicate that the studied system generates social, environmental, and economic benefits exceeding €22.2 million per year, while its operation requires only €43,352 annually. This gives a benefit/cost (B/C) ratio of 512, demonstrating its extremely high social profitability. These results highlight the potential of such infrastructures as nature-based solutions that can enhance water availability both temporally and spatially, mitigate the impacts of extreme events (such as droughts and floods), and strengthen local resilience to climate change. Moreover, they contribute to cultural heritage preservation and promote community cohesion.

1. Introduction

Mountains provide a range of essential ecosystem services, including climate regulation, water-resource conservation, and biodiversity support. They play a crucial role in sustaining ecosystems and delivering benefits at both local and global scales. These ecosystems sustain wildlife and agricultural biodiversity [1], act as carbon sinks [2], regulate the hydrological cycle by ensuring water availability for downstream basins [3], and help mitigate natural disasters, such as floods and droughts [4]. Furthermore, they preserve traditional technologies and knowledge in areas inhabited by indigenous communities.

However, mountain ecosystems remain vulnerable to climate change and extreme weather events. Global warming is expected to alter rainfall patterns, with projections indicating that a 1.5 °C increase in temperature will multiply the likelihood of a drought occurrence by 200%. Similarly, under a temperature rise of 1.5 °C to 3 °C, the probability of flooding is expected to multiply by between 120% and 400% [5]. Prolonged droughts and precipitation events, accompanied by high temperatures, directly impact vegetation and water resource management [6]. Moreover, these regions face rural depopulation and an ageing population [7], as well as agricultural intensification [8]. Changes in land use, such as the abandonment of terraces and artificial wetlands, can lead to the erosion of the watershed’s hydrological regulatory systems [9].

The diverse socio-environmental issues related to water include water scarcity, droughts, floods, and/or water pollution, in addition to the inadequate management of institutions responsible for ensuring access to safe water [10]. These issues negatively impact human development by contributing to biodiversity degradation, food insecurity, socio-economic inequalities, and the impoverishment of populations [11]. Therefore, international organisations, such as UNDP, IUCN, WWF and the EU (European Union (European Commission), International Union for Conservation of Nature (IUCN), United Nations Development Programme (UNDP), and World Wide Fund for Nature (WWF)), recommend adopting more integrated and holistic approaches to water resource management advocating for the protection and restoration of water-related ecosystems, including forests, mountains, wetlands, rivers, aquifers, and lakes [11].

Nature-based solutions (NbSs) can be an alternative solution to social, economic and environmental problems that threaten humanity’s sustainability, such as food and water insecurity, biodiversity conservation, and the reduction of environmental risks, among others. NbSs leverage nature and the services provided by healthy ecosystems to promote human well-being, optimise infrastructure, and safeguard a stable and biodiverse future [12]. Therefore, NbSs present a proposal for low-cost solutions in terms of investment, implementation, and resource consumption, when compared to technological and modern engineering solutions [13,14]. From the governance point of view, the case study presented here highlights a self-managed approach where beneficiaries of aquifer recharge take on both management and costs.

Ancestral Managed Aquifer Recharge Systems in High-Mountain Environments (MAR-HMs) are characterised by (i) being located in the upper parts of mountains, (ii) utilising surplus water during the wet season and infiltrating it into the mountain slopes, (iii) being hydraulic systems that have provided solutions to various problems for hundreds of years, and (iv) being an integral part of the worldview of local communities. These solutions are characterised by their adaptation to the geographical and climatic challenges of the regions, using techniques for efficient water storage and distribution, and especially by their sustainability [15]. In recent years, various studies on MAR-HM have been conducted, whereby significant findings have been revealed regarding the level of water retention in the upper part of the watershed through traditional infiltration systems [16,17,18].

The infiltration channels, developed by ancient civilisations and validated through centuries of operation [19], offer a viable solution to the socio-environmental and economic challenges of today’s modern world [20]. There is growing interest in further studying these systems from various scientific disciplines. The ‘acequias de careo’ of Sierra Nevada serve as an example of an NbS [21]. These are excavated channels built with local materials that transport meltwater from the headwaters of rivers and facilitate its infiltration into the upper slopes. This system ensures water availability during drought periods and supplies irrigation to cultivated fields located on the watershed’s terraces. It is considered an example of Managed Aquifer Recharge (MAR) [22,23].

The study of economic valuation enables the quantification of the various values provided by ecosystem goods and services, including both use values (direct, indirect, and option values) and non-use values (bequest and existence values). There are several methodologies available to achieve a comprehensive quantification of these values and to provide the total economic value (TEV), among which the most notable are methods based on revealed preferences, stated preferences, and benefit transfer techniques. However, this study is focused on use values, for which the cost–benefit analysis (CBA) method is applied, avoiding uncertain estimations.

Several studies report the economic and social value of mountain agroecosystems, traditional irrigation, and infiltration systems, employing an ecosystem services perspective. In this regard, the benefits generated by Mediterranean mountain agroecosystems (Spain) are of both sociocultural and economic nature, estimated at 120 EUR per person/year. These benefits include wildfire prevention, biodiversity conservation, quality food production, water harvesting and the maintenance of cultural landscapes [24].

Traditional irrigated agricultural systems hold high economic value. Alcon et al. in 2022 estimate their contribution to social welfare to range between 9000 and 12,300 EUR/ha/year, and value irrigation water at 1.85 EUR/m³ for the provisioning, regulatory, and cultural ecosystem services it provides [25]. Similarly, Martínez-Paz et al. estimate an average willingness to pay 20 EUR per household/year for the conservation of the traditional irrigated agroecosystem in the Huerta of Murcia (Spain), which is under threat from urban expansion [26].

Rupérez-Moreno et al. assessed in 2015 the environmental economic value of the restoration of the Boquerón aquifer (Albacete, Spain) through artificial recharge. The reported willingness to pay was 21.02 EUR per household/year for use values and 14.86 EUR/year for non-use values, resulting in an aggregate environmental value of 187.46 EUR/year. Notably, 55% of households expressed a willingness to contribute financially, reflecting a high level of local environmental commitment [27].

In Italy, a 2022 study estimated the economic value generated by irrigation channels and fontanili in Lombardy. The biodiversity and recreational values stood out, with a reported willingness to pay (WTP) of 40 and 30 EUR per month/household, respectively [28]. Consequently, the water available in these canals plays both productive and environmental roles.

In Poland, Halytsia et al. conducted a CBA to evaluate managed aquifer recharge (MAR) systems in 2022. Their findings show that both use and non-use benefits exceed the implementation and maintenance costs of the systems. Furthermore, they highlight the use of the CBA method, which is widely adopted for assessing the economic feasibility of MAR projects [29].

Finally, Redrado conducted an economic valuation of the acequias de careo and traditional irrigation systems in the Sierra Nevada region in 2023, employing the CBA method to estimate the benefits associated with these systems. The author extrapolated the willingness to pay (WTP) from a study carried out in an analogous region in south-eastern Spain (Murcia), estimating an annual value of 848,340 EUR. On the other hand, maintenance costs were determined through interviews and records from irrigation communities, amounting to 204,010 EUR per year [30].

Therefore, the objective of this research is to characterise and economically value the operation of ancestral artificial aquifer recharge systems in high-mountain environments, specifically the ‘acequias de careo’ in Sierra Nevada (Spain), by applying a watershed and ecosystem services approach.

2. Case Study

The Bérchules River micro-watershed is located in the central area of the southern slope of Sierra Nevada, in the southern Iberian Peninsula. It forms part of the Guadalfeo River basin and belongs to the Alpujarra region in the province of Granada, Spain. The micro-watershed covers an area of 68 km², with an altitudinal gradient ranging from 979 m above sea level to 2913 m above sea level (m.a.s.l.) [31]. It is bordered by the municipalities of Jérez del Marquesado, Lanteira, Alpujarra de la Sierra, Cádiar, Lobras, Juviles, and Trevélez (Figure 1).

2.1. Territorial Characteristics

The study area is located in the municipality of Bérchules, within the Sierra Nevada Natural Park, designated a Biosphere Reserve since 1986 and a National Park since 1999. The region comprises a high mountain massif, including the Mulhacén (3482 m.a.s.l.) and Veleta (3398 m.a.s.l.) peaks, and hosts 2100 vascular plant species (80 endemic) and rich fauna biodiversity, including over 200 bird species [24]. It also contains the most genetically diverse population of Iberian ibex [32].

The territory reflects a socio-ecological system shaped by traditional agricultural practices in La Alpujarra, where local biodiversity, ancestral knowledge, and indigenous crop and livestock varieties persist [30,33].

Hydrologically, the area is drained by the Río Grande Bérchules (17.3 km) and the Río Chico, both exhibiting a pluvio-nival regime [31]. The study area has a cold climate, with an average temperature of 12.93 °C, which varies with altitude at a vertical gradient of −0.61 °C per 100 m. The coldest months are from November to January, while July and August are the warmest [34]. The climate is cold, with an annual average temperature of 12.93 °C and a lapse rate of −0.61 °C/100 m. Precipitation averages 677 mm/year and evapotranspiration 1033 mm/year, with high seasonality. In the upper watershed, annual precipitation reaches 889 mm, 59% of which falls as snow above 1500 m.a.s.l. [31]. High soil permeability favours aquifer recharge, and snowmelt causes peak flows in spring [18,34,35].

The boundaries of the studied aquifer coincide with the surface of the micro-watershed [18,31]. The average slope is 37%, and the mean altitude is 2070 m.a.s.l. Vegetation includes shrubland, conifers, and grasses adapted to cold and dry conditions [36].

Agricultural settlement dates to the Neolithic, intensifying during the Islamic period (8th–15th centuries) when terracing and irrigation infrastructure were introduced [17,33]. Traditional agricultural systems continue to persist, with cultivated lands accounting for 4% of the total area of the micro-watershed. These lands include fruit trees and both dryland and irrigated vegetable crops and cover approximately 260 ha [36]. Currently, cultivated land occupies around 260 ha (4% of the area), with fruit trees, vegetables (irrigated), and dryland crops, such as oats and almonds [37].

2.2. Description of the ‘Acequias de Careo’ Irrigation System

These are ancestral hydraulic structures consisting of open channels, manually excavated in the soil, which gently descend with slopes of 2 to 3% along the contour lines of the hillside. They are constructed without lining and use local materials [38]. These channels divert water from rivers for infiltration and/or irrigation of agricultural fields. Their dimensions vary, ranging from 0.5 to 2.5 m in width, and extend up to several kilometres in length [16]. They transport water from precipitation and snowmelt from the Sierra Nevada mountains.

There are three types of careo ditches, with different functions: (i) ditches, which infiltrate water along their channel in a high-recharge zone characterized by high permeability, and which operate between October and June; (ii) diversion and transfer ditches, which redistribute meltwater between the Trevélez and Bérchules microbasins between March and June, with a distribution ratio of 3/7 and 4/7, respectively, and that also have infiltration capacity; and (iii) diversion and irrigation ditches, which capture runoff and springs for infiltration from October to June and provide water for irrigation between July and September, located in the lowest areas of the slope. These channels are located in the lower part of the slope.

Nineteen channels have been identified, with a total length of 57.5 km [36]. The total length of the careo channels with infiltration capacity is 21 km, with the most significant ones being “El Espino”, “Real y Nueva”, and “Trevélez y Mecina” (Figure 2). Their operation is seasonal; the careo channels are active during the precipitation and snowmelt periods, while in the summer they become inactive, thereby allowing another network of irrigation channels located in the lower part of the slope to begin diverting water to the agricultural areas [18]. Furthermore, 609 springs have been inventoried in the Bérchules micro-watershed, averaging nine springs per km², 95% of which have flow rates of less than 0.2 L/s, with most of them drying up during the dry season.

Table 1. Water infiltration by the system (adapted from IGME, 2015 [31].

Careo Channels	Type of Channel	Diverted Volume (hm3)	Infiltrated Water Volume (hm3)
El Espino Channel	Careo channel	1.99	1.64
Trevélez Channel	Careo and water transfer channel	0.06	0.06
Mecina Channel		1.2	0.57
Real y Nueva Channel	Careo and irrigation channel	1.44	1.04
Total infiltrated water (hm3)			3.66

contains data from the monitoring of the volume transported and infiltrated by the careo channels within the Bérchules micro-watershed, as evaluated by the Geological and Mining Institute of Spain (IGME) up to the flow-gauging station, between 1 April and 15 May 2015 [31].

According to Table 1, the volume infiltrated by the careo channels amounts to 3.66 hm³, which represents 70% of the flow of the river discharged at the Narila gauging station (5.3 hm³) and contributes to 48% of the total aquifer recharge (7.62 hm³), estimated through modelling. The difference is considered natural recharge, that is, diffuse recharge, which accounts for 52% of the total recharge. Moreover, it was estimated that the ancestral system of artificial recharge of high-mountain aquifers, the careo channels in Bérchules, has an artificial and natural recharge capacity of 4.8 ± 2.0 hm³/year and 7.4 ± 10.6 hm³/year, respectively [21].

3. Materials and Methods

3.1. Materials

The materials employed to identify and characterise the potential benefits for the economic valuation of the ‘acequias de careo’ channel systems came from primary and secondary sources (both quantitative and qualitative) from various institutions, including the Ministry of Agriculture, Fisheries, and Food, the Regional Government of Andalusia, and the Municipality of Bérchules.

A table of predominant crops was constructed, and the gross value added (GVA) was determined (see Appendix A). To estimate the benefits generated by the system, variables reported in scientific articles, and in undergraduate and postgraduate theses were analysed. In order to characterise the functioning mechanism and benefits, and to estimate the volume of water regulated by the system, information was used from the final report of the hydrogeological research of high-mountain aquifers subjected to intensive groundwater use in the headwaters of the Bérchules River.

To understand the management of the careo channels, semi-structured interview forms were applied to three representatives of the Bérchules irrigation board (president, water distributor, and farmer). An observation form was used to describe the operation and general characteristics of the system.

Once the potential benefits provided by the system were identified, the cost–benefit analysis (CBA) method was applied to estimate the total economic value.

3.2. Method: Cost–Benefit Analysis (CBA)

The cost-benefit analysis (CBA) method is a unidimensional approach employed to assess the feasibility of projects from a monetary perspective. Thanks to its simplicity, comparisons between factors can be made due to its high commensurability. Benefits are valued by the satisfaction of preferences, and costs by dissatisfaction; in evaluating advantages and disadvantages, it is possible to assess the change in welfare. In practice, all indicators should be referred to in monetary units, as explained below. CBA has been used for hydro-economic decision-making, such as measures for watershed conservation [39] and aquifer recharge [40]. More recently, Hurtado and Berbel have conducted a CBA for the nearby watershed of Guaro (Axarquia, Malaga) 60 km west of the Bérchules sub-basin [41].

The method consists of three phases, which are defined in Figure 3.

The CBA is carried out by comparing the advantages and disadvantages of investing in the restoration and/or maintenance of the systems. The benefits are compared with the associated costs within a common analytical framework with defined spatial and temporal boundaries. Since these costs and benefits are related to a wide range of impacts measured in widely different units, a monetary value is assigned as the common denominator to enable meaningful comparisons. For measures that have no market value, the monetary value has been obtained through stated preference methods (Contingent Valuation Method).

The method consists of the following phases: (1) definition of the scenario and system boundaries; (2) selection of indicators; and (3) estimation of costs and benefits.

3.2.1. Cost Estimation

In the cost analysis of artificial aquifer recharge systems, capital costs, operation and maintenance costs, and, where applicable, financial costs (debt service) are considered. Capital costs (incurred only once at the beginning) include land acquisition; project design and formulation; feasibility analysis; permits and construction supervision; construction costs and operational testing; and operation and maintenance costs, which include labour, electricity, regulatory testing requirements (e.g., water quality tests), and maintenance costs (e.g., channel cleaning, earthmoving, well rehabilitation) [23].

For the annualised cost, the concept of Equivalent Annual Cost (AEC) is used, determined through Equation (1), as applied by [43] for water economics:

$$\mathrm{A}\mathrm{E}\mathrm{C}={\displaystyle \frac{\mathrm{r}·{(1+\mathrm{r})}^{\mathrm{n}}}{{(1+\mathrm{r})}^{\mathrm{n}}-1}}·\mathrm{K}+\mathrm{O}\mathrm{M}\mathrm{C}$$

(1)

where K represents the investment costs, OMC are the operating and maintenance costs, r is the discount rate, and n is the project or measure’s lifespan.

For natural infrastructure projects, we propose using a discount rate of r = 4%.

3.2.2. Benefit Estimation

The induced benefits method was utilised, which identified both direct and indirect benefits. The direct benefits are (i) the net value of agricultural production for which the Gross Added Value (GVA) of crops irrigated with recharge water was estimated; (ii) thte creation of agricultural employment, estimated using the average agricultural GVA per employment according to National Statistical Institute (INE); (iii) net CO₂ capture per year; and (iv) the impact on biodiversity and the landscape.

The indirect benefits are (i) agro-food processors and transport and (ii) an increase in employment due to the induced economic activity in non-agricultural sectors.

3.2.3. Estimation of the Benefit/Cost Ratio

This was determined by calculating the ratio between the total benefit generated and the total costs.

3.3. Definition of Scenarios and System Boundaries

For the CBA, the first step involved the definition of a measure that generates a set of direct and indirect benefits, such as the maintenance of the careo channel system in the Bérchules microbasin, with a potential careo/infiltration and flow regulation capacity of 4.8 ± 2.0 hm³/year during the wet season [16], so that, during the dry season, water resources are available from springs to meet the demand generated by agricultural activities under irrigation.

Subsequently, the potential costs and direct and indirect benefits that the measure generates for society were identified. To identify the benefits, the following principles were considered [44]: (i) the careo channel system is a main component, integrated and complementary to natural ecosystems and mountain agroecosystems; (ii) these are low-cost hydraulic infrastructures of ancestral origin, built with local materials; (iii) this is an ancestral solution based on nature; (iv) it forms part of the traditional agroecosystems, with terraced fields that require more water during the summer season (July–September).

Figure 4 schematically shows the determination of the direct and indirect results of the adopted measure.

3.4. Selection of Indicators

Indicators were selected that enabled the total economic value to be approached, and values were chosen that are of direct and indirect use. For future studies, the quantification of non-use values (option value, existence value, and others) and immeasurable values was left aside. The selected indicators are shown in

Table 2. Selected indicators for valuation.

Type	Indicators
Costs	(a) Direct and Indirect Conservation and Operation Costs
Benefits	(b) Increase in Agricultural Value Generation
	(c) Increase in Employment in Agricultural Activities
	(d) Improvement in Water Supply Reliability
	(e) Increase in Tree Crops (CO2 Capture)
	(f) Increase in Induced Tourism
	(g) VAB Multiplier in the Rest of the Economy (Non-Agricultural)
	(h) VAB Employment in the Rest of the Economy (Non-Agricultural)

.

4. Results: Cost–Benefit Analysis of the Careo Channels

4.1. Estimation of Costs

(a)

Direct and indirect conservation and operation costs:

• Direct costs: The Bérchules irrigation community hires a person known as the ‘acequiero’, who is responsible for carrying out the cleaning, maintenance, and operation tasks for the irrigation canals. To perform these duties, various resources are required, including a means of transportation (car), fuel, labour tools, and a mobile phone.
• Indirect costs: The irrigation community has a board of directors responsible for planning, organising, and overseeing the operation of the careo channels. To this end, they hold meetings and assemblies to make decisions that ensure the proper functioning of the irrigation system. At the end of each summer, before the wet season begins, the acequiero inspects the canals and identifies defective sections. Subsequently, in coordination with the irrigation community, a group of workers is hired to carry out cleaning and/or rehabilitation tasks. The cleaning process involves removing vegetation, rocks, accumulated sediments, and other elements obstructing the water flow. In certain cases, this may require the use of machinery and specialised personnel, especially when landslides occur along the irrigation canals.

For cost estimation, reference is made to the study conducted by Redrado in 2023 [30], which provides the following direct and indirect conservation costs, which are shown in

Table 3. Total costs of the Bérchules irrigation community (retrieved from [30]).

Conservation Cost of the Irrigation Communities of Bérchules Channels (per year)
Direct Conservation Costs
Acequia de Trevelez	EUR	14,018
Acequia de El Espino	EUR	7466
Acequia Real y Nuevo	EUR	5668
Subtotal of Direct Costs	EUR		27,152
Indirect Conservation Costs
Period from March to November	EUR	16,200
Subtotal of Indirect Costs	EUR		16,200
Total Annual Conservation Cost	EUR		43,352

.

Using the volume of infiltrated or recharged water (Table 1) and the total annual cost (Table 3), the cost per unit volume of water was determined to be 43,352/4.86 = 0.009 EUR/m³. Therefore, the total cost amounts to 0.043 × 106 EUR/year.

4.2. Estimation of Benefits

Two types of benefits are defined: direct and indirect, to estimate the total. Direct benefits are services received by the economic activity or population involved in the measure “Maintenance of Careo Channels in the Bérchules micro-catchment”, while indirect benefits are those generated by the action to the rest of the economy as a multiplier effect, thereby stimulating economic activities and generating employment.

(a)

Increase in the value generated in agriculture. It was assumed that, on average, 4.8 hm³/year of the careo channel water is allocated to agricultural production under irrigation, and the GVA of the weighted average of the irrigated crops in the area was determined. The results are attached in Appendix A. The main crops include almonds, olives, vineyard grapes, greenhouse produce, wheat/oats, vegetables, and other irrigated herbaceous crops [37].

In order to determine the economic value of the change in the crop pattern, economic indicators were estimated (gross margin and GVA), which were calculated using the weighted average of the seven predominant crop types in the area. In this regard, the gross margin of the “typical” crop is obtained by subtracting income from direct costs, machinery, and paid labour, which amounts to 8143 EUR/ha.

For the determination of the GVA, the irrigable area is multiplied by its unit GVA. The irrigable area with 4.8 hm³ of water for the “typical” crop has a net water consumption of 4067 m³/ha, which amounts to 1180 ha. To calculate the GVA, the GVA per hectare is multiplied by the irrigable area.

Direct GVA = 1180 ha × 8143 EUR/ha = 9610,111 EUR/year

(2)

Lastly, this means that the available water volume of 4.8 hm³/year allows the GVA in the area to increase by 9,610,111 EUR/year, which equates to approximately 2.0 EUR/m³.

(b)

Increase in Agricultural Employment. In addition to this direct effect of GVA increase in Equation (2), the careo channel system in the Bérchules micro-catchment would have an indirect multiplier effect on generating employment in agricultural activities. To assess this effect, the number of jobs generated by the benefit amount was determined. To calculate the number of jobs created by agricultural activities, we divided the agricultural GVA by the GVA per agricultural job, which amounts to 40,573 EUR/job (INE, 2025). This, therefore, corresponds to 237 jobs.

Each job generates an average agricultural salary, which, according to INE (2025), amounts to 13,608 EUR/year [45]. The increase in employment in a rural area that is losing its population increases social welfare. To measure the social benefits of maintaining and/or creating a job in this context, we assume a proposal by Borrego-Marín et al., who argue that, in labour markets with high unemployment, such employment changes can yield significant net efficiency benefits, which should be included as a benefit in the CBA, and propose that welfare benefits can be estimated at 70% of salaries [46]. Therefore, the welfare benefit generated by the salary earned is 9526 EUR/job (70% of the salary received). This value aims to capture the improvement in social welfare within the locality. Subsequently, the economic value contributed by job creation in agricultural activities can be determined. To this end, the number of generated jobs is multiplied by the welfare benefit obtained for each job, which amounts to 2,260,000 EUR/year.

(c)

Increase in water supply guarantee. Water supply companies, in order to ensure water purchase rights in the case of drought, maintain water reserves for emergency events, thereby guaranteeing water supply. To assign the corresponding value, we reviewed the literature and obtained the following indicators:

Case (1) Australian water markets (high reliability): These water rights are more reliable, and holders typically receive their full allocation even in dry years. Price: According to the most recent data, high-reliability water rights in the Murray-Darling Basin, particularly in the connected southern system (such as the Murray, Goulburn, and Murrumbidgee rivers), can range from 3000 to 8000 AUD per megalitre (ML). Prices fluctuate based on seasonal conditions, water availability, and demand. A reference value of 5000 AUD/hm³ is assumed, which equals 5 AUD/m³ (or 3.0 EUR/m³), which is a ‘capital value’. To convert to an annual value, we use the 4% interest rate, resulting in an equivalent annual value of 0.12 EUR/m³.

In Australia, values can also be found for low-reliability (or low-security) water rights. These rights are less reliable, and allocations are often reduced or unavailable during dry periods. Price: Low-reliability water rights typically cost less, ranging from 300 to 1500 AUD per megalitre, depending on the region and water availability. We use a reference value of 1000 AUD/hm³, which is equivalent to 1 AUD/m³ (0.6 EUR/m³).

To calculate the value of the guarantee of water supply, the difference between the two types of water rights should be considered, which is 2.4 EUR/m³ (3.0 EUR/m³–0.6 EUR/m³). These values represent a ‘water-right value’ with a ‘permanent capital’ nature that must be converted to a ‘spot price’ (for a season). The application of a discount rate of 4% results in 0.096 EUR/m³ since all economic values are annualised.

Case (2) Borrego-Marín et al. propose the value of 0.06 EUR/m³ for the increase in guarantee at the watershed level for a CBA analysis in Guadalquivir water conservation measures [46].

Case (3) Mesa-Jurado et al. estimate the willingness to pay for an increase in guarantee among olive growers in Jaen (who have a very low ex ante guarantee level) to be in the range of 0.034 to 0.074 EUR/m³ [47].

Case (4) EMASAGRA (Metropolitan Water Company of Granada) currently maintains ‘drought emergency wells’ that are fully operational on a continuous basis, although they have not been used since 1995, with a cost of approximately 200,000 EUR/year [48] for a total demand of 21.6 hm³, which equals approximately 0.01 EUR/m³.

Out of all these, the lowest reference values were chosen, those observed in the Australian market and in EMASAGRA (the most conservative). Therefore, a price of 0.01 EUR/m³ was used for the guarantee of water supply. Consequently, to determine the value of the increase in water supply guarantee, the volume of water from the measure was multiplied by the guaranteed price, which amounts to 48,000 EUR/year.

(d)

Increase in tree crop cultivation (CO₂ capture). With an average of 4.8 hm³/year of water, 1180 ha of a “typical” crop are irrigated, including tree crops; it is considered that tree crops represent 20% of the total. According to Tocados-Franco et al. in their study of 2024, the CO₂ capture is 6 t/ha/year, and, thus, a total of 1416 t of CO₂ is captured [49]. The analysis of the carbon rights market in the EU for 2023 determines that the average value of each ton of CO₂ is 70 EUR/t. To determine the economic value of the increase in CO₂ capture, we multiply 1416 t by 70 EUR/t, which results in 99,120 EUR/year.

(e)

Increase in induced tourism. The careo channels are ancient hydraulic systems integrated into a traditional agricultural system, of which the terraces form part. They are also part of a landscape of great biological value, such as the Sierra Nevada National Park, which represents a tourist resource. In this regard, Sayadi et al. report in their study that the average willingness to pay (WTP) for accommodation with scenic views, including an agricultural irrigated component on intermediate slopes with some visible village or traditional houses on the landscape, is 31.60 EUR/day [50]. This is significantly higher than the lower-valued landscape (landscapes of abandoned agricultural land with no villages in sight and steep slopes), which was estimated at 21.48 EUR/day. Therefore, the results of the study are highly relevant because they demonstrate that the terraced irrigation system in the Alpujarra has a societal benefit beyond just its productive value, thereby justifying the value included in the CBA.

Similarly, using data from the Diputación de Granada (2020), the number of overnight stays in the area was determined [51]. Accommodations for a total of 4665 visitors were identified with an occupancy rate of 31%. When multiplied by 365 days a year, this results in 527,845 people/year. Additionally, it was considered that only 1% of tourists visit the careo channels; therefore, the increase in tourists visiting the careo channels is 5278.4 people/year. According to INE (2023), the average spending on rural tourism is 85 EUR/person [52]. In this analysis, it was assumed that the GVA generated by tourism in the area is 50% of the average spending, which amounts to 42.5 EUR/person. The product of 5278.4 people/year by 42.5 EUR/person results in a value of 224,332 EUR/year. Therefore, the careo channels also contribute towards improving tourism and the landscape and towards generating economic activity.

(f)

Multiplier of GVA in the rest of the economy (non-agricultural sectors). The growth of the agricultural sector produces a multiplier effect in industry (mainly agro-food processors, but also in other complementary industries) and in services (mainly transportation and service providers to farms and food processors). Borrego-Marín and Berbel used the irrigation multiplier for California in 2018, which is estimated at 1.49 (i.e., for every euro generated in agriculture, 0.44 EUR is induced in the rest of the economy) [53]. However, in our case, a local estimate of 1.80 was used, based on input–output tables for Spain [54]. This means that for every euro of added value in the agricultural sector, 0.80 EUR is generated in surrounding industries and services (input production and product processing). To determine the GVA in the remaining non-agricultural sectors, the increase in the agricultural value was multiplied by 0.80.

GVA employment in the rest of the economy (non-agricultural sectors). The multiplier effect of water in agriculture indirectly reaches the generation of jobs in the rest of the non-agricultural economy. To determine the GVA of employment in the rest of the economy (non-agricultural sectors), we start by calculating the number of jobs generated. The value of the GVA in the rest of the economy amounts to 7,687,314 EUR/year, and according to the INE (2022), the GVA per non-agricultural job is 63,799 EUR/job [45]. Therefore, the number of jobs generated = 7,687,314 EUR/year/63,799 EUR/job = 120 jobs/year.

According to INE (2022), each job generates an average non-agricultural salary of 26,948 EUR/year, but from this amount, the welfare benefits can be estimated as 70% of the direct effect of labor demand on income, which amounts to 18,864 EUR/job [45]. Subsequently, the welfare benefit generated per non-agricultural job is calculated as follows: Welfare benefit per non-agricultural job = 120 jobs × 18,864 EUR/job = 2,272,926 EUR/year.

Table 4. Results of the economic valuation of the careo irrigation system in the Bérchules micro-catchment.

	Cost Elements	Base Indicator	N° of Units	Unit	EUR/Unit	Unit	Total (106 EUR)
(1)	Conservation and operation costs	Cost per m3 of water	4.80	hm3	0.009	EUR/m3	0.043
(2) = (1) Total operation and management cost							0.043
	DIRECT BENEFITS
	Provisioning Services	Base Indicator	N° of Units	Unit	EUR/unit	Unit	Total (106 EUR)
(3)	Increase in agricultural value	GVA	8143.3	EUR/ha	1.180	ha	9.609
(4)	Increase in agricultural employment	Employment	236.8	jobs	9526	EUR/jobs	2.256
(5)	Increase in water-supply reliability	Water saved	4.8	hm3	0.01	EUR/m3	0.048
(6) = (3) + (4) + (5) Total provisioning services							1.913
	Regulating Services	Base Indicator	N° of Units	Unit	EUR/unit	Unit	Total (106 EUR)
(7)	Increase in tree crops (CO2 capture)	ha	1416.0	t/year	70	EUR/t (CO2eq)	0.10
(8) = (7) Total regulating services							0.10
	Cultural Services	Base Indicator	N° of Units	Unit	EUR/unit	Unit	Total (106 EUR)
(9)	Increase in induced tourism	Tourism system	5278.4	people/year	42.5	EUR/persons	0.22
(10) = (9) Total cultural services							0.22
(11) = (10) + (8) + (6) Total direct benefits							12.24
	INDIRECT BENEFITS	Base Indicator	N° of Units	Unit	EUR/unit	Unit	Total (106 EUR)
(12)	GVA multiplier in the rest of the economy (non-agricultural)	Multiplier	0.8	--	--	--	7.687
(13)	GVA employment in the rest of the economy (non-agricultural)	GVA/non-agricultural employment	120	jobs	18,864	EUR/job	2.273
(14) = (12) + (13) Total indirect benefits							9.96
(15) = (14) + (11) Total benefits							22.20
(16) = (15)/(2) BENEFIT-COST RATIO							512.01

presents the consolidated economic valuation of the careo irrigation system in the Bérchules River microbasin, highlighting the increase in agricultural value, job creation, and the multiplier effect in the rest of the economy—values that generate the greatest economic benefits to society. The benefit/cost ratio (BCR) is 512, indicating that for every euro invested in maintenance and operation costs, the careo system generates 512 euros in societal benefits.

5. Discussion

The ‘acequias de careo’ MAR network in the Bérchules micro-watershed generates societal benefits exceeding 22.2 million EUR/year, with maintenance and operation costs amounting to 43,352 EUR/year. The main contributors to these economic benefits are the increase in agricultural value, job creation, and the multiplier effect on the broader economy. Furthermore, the benefit/cost ratio reaches 512, meaning that for every euro invested in maintenance and operation, the careo irrigation channels generate 512 EUR in societal benefits. In regions experiencing water scarcity, the implementation of MAR systems in a watershed is highly positive, as the total economic value exceeds the capital and operational costs of such systems [29]. In this regard, various studies highlight the substantial economic value generated by MAR systems.

Redrado performed a CBA analysis of the Bérchules careo system, estimating a benefit/cost ratio (BCR) of 4.16 [30]. Redrado quantified the benefits by adopting a willingness-to-pay (WTP) estimate from a contingent valuation study conducted on traditional irrigation systems in a different region (Murcia). However, our study determined a significantly higher ratio of 512.

Rupérez-Moreno et al. concluded that the implementation of MAR systems generates a positive net present value (NPV) and an internal rate of return (IRR) greater than 50% in irrigated agricultural areas in Spain [27]. Similarly, Halytsia et al. estimated that expanding the MAR system for human consumption in the city of Tarnów (Poland) would yield an NPV of 12.1 million EUR over 30 years [29]. Furthermore, Hutton in 2012 highlighted that improving water supply and sanitation systems is highly cost-effective, with each dollar invested generating between 5 USD and 46 USD in benefits across all sub-regions of the developing world [55]. More recently, a study published in 2022 that analyzed 21 MAR systems in 15 countries concluded that the benefits systematically exceed the costs, with BCR ratios ranging from 1.3 to 10.0 [56].

Nevertheless, our results exceed these estimates by a factor of 50, primarily because MAR-HM systems do not incur capital costs, having been in continuous operation for over 1000 years. Moreover, their operation and maintenance costs are minimal and are borne by the local community, with low bureaucratic expenses. The watershed-scale analysis and ecosystem services approach employed in this study have enabled the identification and quantification of a wide range of direct and indirect benefits, which have significantly increased the estimated economic value of these systems.

This year (2025), the Guadalquivir Basin Authority is analysing the feasibility of recovering an ancient ‘careo system’ that has been abandoned in the nearby Dilar watershed (also in Sierra Nevada) [57]; in this case the cost will need to include the capital cost required to recover the ancient system in the evaluation of a CBA that will probably show positive values although maybe lower than those of the Bérchules system.

It can also be highlighted that, in a systematic literature review evaluating the application of NBS in groundwater recharge management, MAR was successful in increasing recharge in 50 of the 61 studies reviewed (81.96%) [58]. However, despite their historical effectiveness, “careo channels” now face increasingly complex challenges. Climate change, with its impact on the availability and seasonality of rainfall, threatens to destabilize the delicate hydrological balance that these ancestral infrastructures have maintained for centuries. The decrease in snow cover, premature melting of snow, and more frequent torrential rains alter flows and interfere with the ditches’ ability to infiltrate and distribute water in a sustained manner [59]. In addition, socioeconomic factors, such as rural depopulation, the abandonment of agriculture, and pressure from mountain tourism, hinder collective management and maintenance [60].

Faced with this scenario, it is urgent to articulate adaptation strategies that recognize the heritage, environmental, and functional value of “careo channels”. Recent projects have successfully explored the integration of local knowledge with technological tools, such as flow sensors, remote sensing, or participatory mapping, to strengthen their resilience [60]. Furthermore, institutional recognition as a hydraulic heritage and agroecological system has begun to open up new possibilities for financing and technical support. In this context, careo irrigation ditches can and should be considered not only as vestiges of the past but also as adaptive solutions for a future marked by climate uncertainty [61].

In order to fully understand the future viability of “careo channels”, a more exhaustive analysis of the risks and uncertainties they face is necessary. For example, the financial sustainability of communal systems, which have historically been sustained by collective work and voluntary maintenance, currently faces significant challenges, such as rising costs associated with infrastructure rehabilitation and the potential incorporation of new technologies, which are generating tensions in their operation. This economic vulnerability is accentuated by demographic dynamics, such as rural depopulation, population aging, and youth migration, which hinder generational change and weaken the social capital necessary for the management and continuity of these systems [60].

At the same time, external factors, such as changes in water, agricultural, or land-use planning policies, can negatively impact “careo channels” if they are not duly recognized within regulatory frameworks. The lack of explicit inclusion in hydrological or climate change adaptation plans limits access to technical and financial resources and can even lead to conflicts with new regulations that favor more centralized or technically advanced management models [62]. Given this situation, it is essential to incorporate prospective analysis tools, such as multicriteria analysis and various planning scenarios, that allow for the assessment of the ecosystem, cultural, and social benefits offered by these systems. In this way, evidence can be generated to support more inclusive and sustainable public policies, capable of preserving irrigation ditches as key infrastructure for water management in the face of a future marked by climate uncertainty and rural transformation.

6. Conclusions

The acequias de careo system in the Bérchules microbasin is an NbS that generates societal benefits exceeding 22.2 million EUR per year, with maintenance and operation costs of 43,352 EUR per year, resulting in a benefit/cost ratio of 512. This means that for every euro invested in the maintenance of the careo channels, 512 EUR in benefits are generated. The economic valuation is based solely on marketable values, excluding intangible benefits, such as existence, legacy, and option values.

The acequias de careo system in the Bérchules microbasin constitutes a highly efficient nature-based solution (NBS), generating estimated social benefits of more than €22.2 million annually, compared to maintenance and operating costs of €43,352 per year. This difference translates into a cost/benefit ratio of €512, meaning that for every euro invested in maintenance, €512 in benefits are generated. It should be noted that this economic valuation was based exclusively on market prices, excluding intangible benefits, such as existence value, legacy value, or option value.

Quantifying the benefits was possible with reliable hydrological data on infiltrated water volume at the microbasin level, obtained through a hydrogeological study. The analysis identified multiple ecosystem services associated with the system, such as landscape value, biodiversity promotion, and mitigation of natural hazards, such as floods and droughts. However, these benefits have not been valued economically due to the scarcity of available data in comparable contexts.

The system’s maintenance and management are actively handled by the local population. Thus, the irrigation community assumes direct responsibility for its operation, hiring irrigation diggers and receiving incentives from the municipalities located in the lower part of the basin, in a joint effort to achieve efficient and sustainable management of water resources.

It is recommended that future studies in the field of risk management and natural disasters delve deeper into the mitigation capacity of these systems in the face of droughts and floods, as well as the economic estimation of avoided damages. The Bérchules case exemplifies a self-funded community governance model, in which users who benefit from recharge also assume responsibility for its management. However, multiple governance models exist internationally, ranging from communal approaches or Payments for Ecosystem Services (PES) systems, such as the amunas in Peru, to altruistic pro-environmental behaviors (as in certain areas of Almería), and even initiatives driven by public policies, such as in the Dílar River basin, promoted by the Water Agency. This diversity of approaches demonstrates the versatility and validity of ancient recharge systems as key tools for integrated water management in mountainous regions.