Vulnerability assessment of groundwater resources: A modelling-based approach to the Mancha Occidental aquifer, Spain
Introduction
The Mancha Occidental aquifer, central Spain, spans an area of 5500 km2 and is home to approximately 300,000 people (Fig. 1). The area presents a continental semiarid climate, where long dry periods alternate with short wet sequences, and hot dry summers follow short mild winters. Average rainfall is approximately 415 mm/yr and potential evapotranspiration is on the order of 1200 mm/yr. Temperatures range from an average 5 °C in winter to about 25 °C in summer.
Together with Toledo and its surroundings, the Mancha Occidental aquifer boasts the most dynamic economy of the Castilla-La Mancha state, an otherwise depressed and scarcely populated region (Fornes et al., 2000).
Groundwater is by far the most valuable water resource in the area. Aquifer-based irrigation accounts for 95% of the total uses, corresponding to an irrigated surface in excess of 200,000 ha (Guadiana Water Authority, 2007). Intensive groundwater development began in the 1970s, mostly through the initiative of individual farmers. Since then, irrigation has brought significant social and economic benefits to the region, mainly due to the ready availability of groundwater on demand and to the reliability of aquifers during droughts (Hernández-Mora et al., 2003, Garrido et al., 2006).
However, groundwater development mostly took place in an uncontrolled manner, while Spain's water authorities traditionally focused on building and managing surface water infrastructures (Llamas and Martínez-Santos, 2005). This led to significant management uncertainties, particularly in regard to pumping and irrigation data, an occurrence which, on the other hand, seems commonplace in many semiarid regions of the world (Shah, 2004, Kretsinger and Narasimhan, 2006).
Pumping caused noteworthy water table drawdowns, severely affecting valuable groundwater-dependent wetland ecosystems such as the “Mancha Humeda” UNESCO Biosphere Reserve or Ramsar-listed “Las Tablas de Daimiel” National Park (Llamas, 1988, Martínez-Alfaro and Castaño, 2001). European subsidies favouring irrigation of water-intensive crops contributed to aggravate these effects during the 1980s and 1990s (Bromley et al., 2001). In recent years, and despite different water-saving initiatives, downward water table trends have not been reversed (IGME, 2004).
This had led to a Significant conflict between environmental conservation groups and farmer collectives have arisen as a result. These are however not the only disputes at the basin scale. Official estimates state that over a half of the existing wells in the area are unlicensed (Guadiana Water Authority, 2005). Unlicensed abstraction not only poses a considerable uncertainty in regard to the area's water uses, but it is also one of the main sources of friction between the Guadiana Water Authority (the agency responsible for groundwater management in the catchment) and farmers (the main groundwater users). Several attempts have been made to correct this situation, ranging from top-down command and control approaches to compensatory payments for farmers to voluntarily cut down on water use (Varela-Ortega et al., 2003). These have traditionally fallen short of potential, largely due to the heterogeneity of views held by the different farmer lobbies, to the existence of illegal pumping and to the lack of coordination between the agencies responsible for implementing water and agricultural policies. Conflicts between farmers and the Water Authority are fuelled by a sense of urgency derived from the EU Water Framework Directive, which establishes an obligation to all Member States to recover a good ecological status of their surface and groundwater bodies by 2015.
A dropping water table (1 m/yr in some areas over the past 30 years) has also raised concerns as to the sustainability of the current situation. Even if agriculture is steadily losing importance as an economic sector, aquifer exhaustion is seen as potentially serious threat in the mid-term (Guadiana Water Authority, 2005). This is because irrigated agriculture still provides an important part of the employment in some municipalities, and also because it is the base for a significant share of the area's industrial sector.
In such a situation, where conflict is commonplace, water data uncertain and sustainability an issue of concern, involvement of the main social actors is perceived as essential in order to devise a sustainable water plan for the future. Within the context of a larger-scale project this paper describes the development of a tool to facilitate the transition to adaptive water management at the basin scale. Adaptive water management is already widely discussed in the literature (Lee, 1999, Stankey et al., 2003, Pahl-Wostl, 2006a). For the purpose of this paper it should suffice to say that public participation is a becoming feature both to adaptive management regimes and to the EU Water Framework Directive (European Commission, 2003, Henriksen et al., 2007). Thus the project seeks to involve stakeholders and water managers from the very outset, asking them what management problems and uncertainties they face and what sort of tools they require to address them.
From the above description it could be inferred that Mancha Occidental water managers and stakeholders currently face a variety of problems. Farmers have significantly depleted the Mancha Occidental aquifer since the 1970s, and they now believe groundwater will eventually run out. They wish to know when and where that is more likely to happen, since groundwater is the only water resource they can rely on. On the other hand, the Guadiana Water Authority must ensure a complete recovery of the aquifer and its associated ecosystems within the deadlines established by the EU Water Framework Directive (2015, or ultimately, 2027). In order to comply, they need to factor into pumping plans how much water needs to be saved on a yearly basis. This information is also of interest for farmers and environmental conservation groups, since the former must forfeit the water and the later play an active role as ecosystem restoration advocates.
Controversies therefore boil down to establishing the system limits and evaluating potential tradeoffs between irrigation water demands and environmental flows. As explained later, consultation with Mancha Occidental stakeholders led to the conclusion that these issues could be assessed by means of appropriate decision-support systems, in this case a numerical groundwater flow model.
Section snippets
Objectives
This paper focuses on the development and participatory application of such a model. The model is in essence a mathematical replica of the physical system, able to dynamically reproduce its behaviour. It is used to simulate aquifer evolution within a series of scenarios, which are drafted according to stakeholder opinion. Modelling work ultimately aims at testing the vulnerability of the system (and hence the stakeholders’ own) by considering a range of tradeoff alternatives between
Methodology
Research is carried out in three main stages namely: (1) stakeholder analysis and engagement, (2) model development and participatory scenario design, and (3) scenario simulation. The first step essentially consists in ensuring a representative stakeholder base, striving to involve all key water actors in the process. This stage includes both a decision on the part of all participants as to how the participatory process should be run and a explicit definition of the existing research needs.
Discussion
Stakeholder involvement within the project was evaluated externally in order to ensure a fair process and outcome (Table 4). Stakeholder perceptions were compiled in two different reports which provide the basis for most of the following paragraphs (Correa, 2007a, Correa, 2007b).
From an overall point of view, the stakeholders consider the methodology to be an innovative and welcome addition to the basin. They also see this exercise as something useful in the sense that it has helped them to
Conclusions
In a world of rapid change, water policy is frequently constrained by growing management uncertainties. These may not only stem from the hydrological systems under consideration but also from exogenous decisions or hazards. While it is unrealistic to pretend that these uncertainties can be completely dispelled, this participatory exercise shows that inclusive stakeholder processes and adequate technical tools may prove a beneficial in narrowing down and improving stakeholder understanding about
Acknowledgements
This paper summarises some of the main findings of the first author's Ph.D. dissertation (Martínez-Santos, 2007), carried out with a scholarship of the EU-funded NeWater project (GOCE contract 511179). The authors would like to thank the research teams from the Department of Geodynamics of the Universidad Complutense de Madrid, the Department of Agricultural Economics of the Universidad Politécnica de Madrid and the Geological Survey of Spain, for their ongoing involvement in the project and
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