Contribution of decision support systems to water management improvement in basins with high evaporation in Mediterranean climates


 The entry into force of Directive 2000/60/EC of the European Parliament and the Council of 23 October 2000 established a new model for the management and protection of surface water and groundwater in Europe. In this sense, a thorough knowledge of the basins is an essential step in achieving this European objective. The utility of integrative decision support systems (DSS) for decision-making in complex systems and multiple objectives allows decision-makers to identify characteristics and improve water management in a basin. In this research, hydrological and water management resource models have been combined, with the assistance of the DSS AQUATOOL, with the aim of deepening the consideration of losses by evaporation of reservoirs for a better design of the basin management rules. The case study treated is an Andalusian basin of the Atlantic zone (Spain). At the same time, different management strategies are analysed based on the optimization of the available resources by means of the conjunctive use of surface water and groundwater.


INTRODUCTION
Water resources are under increasing pressure associated with population growth, the development of economic activities and the potential scenarios of climate change that predict a significant decrease in precipitation and streamflows (Alcamo et al. ; González-Zeas ).
Water resource management includes two basic components and their relationships. On the one hand, the sources of the resource must be managed; on the other hand, water demand must be met. In relation to the latter, irrigated agriculture is the main demand for water, with consumption of more than 70% of the total freshwater of the world. In fact, in some basins, water management is focused almost exclusively on supplying agricultural demands, as is the case of this study on the Barbate River basin (Cádiz, Spain). Measures aimed at more efficient use of water in agriculture have been developed in recent times. Strosser these extend from the first models (Tyagi & Narayana ), whose objectives were to define the amount of surface water and groundwater needed for irrigation, to the most recent (Rezapour Tabari & Soltani ; Singh c), in which a very high number of sources and demands are simulated to optimize the resource by means of programming techniques in constant evolution (Condon & Maxwell ). Therefore, currently, the DSS are supported by easyto-use computer software such as AQUATOOL (Andreu et al. ), WARGI (water resources system optimization aided by graphical interface) (Sechi & Zuddas ) and AQUATOR dveloped by Oxford Scientific Software in 2001.
Surface water and groundwater are two components that interact according to climatic, terrain relief, geological and biotic factors (Sophocleous ). Therefore, an impact on one of them will inevitably affect the quantity and quality of the other (Tanvir Hassan ). However, surface water and groundwater have traditionally been considered as two distinct and independent components of the hydrological cycle. In the 1970s, the concept of 'hydroschizophrenia' appeared, a term proposed to designate the mental separation that people make between the superficial waters (that they see) from the subterranean (that they do not see). Since then, consciousness has developed about the importance of the interactions of these two components of the hydrological cycle to meet human needs, as well as ecological functions in riparian zones and other dependent ecosystems. In addition, current legal regulations such as the Water Framework Directive (EP ) have led to a major research activity on issues related to joint management.
This research is part of a project that has the support of the Ecological Transition Ministry (Government of Spain), through the Biodiversity Foundation, in the matter of climate change. Its main objective is to deepen the knowledge of the management of an Andalusian hydrographic basin in the Atlantic zone (Spain) and to analyse the possible management strategies based on the optimization of the available resources by means of the conjunctive use of surface water and groundwater, helping managers to decide which management is the most suitable. For this aim, the decision support system AQUATOOL and its SIMGES module have been used. As a characteristic element of this basin, the only surface reservoir with multiannual regulation capacity has a significant loss due to direct evaporation. Therefore, the contribution of the DSS to the quantification of this output of the balance has been analysed, and management alternatives aimed at mitigating this water problem have been proposed.

General characteristics of the Barbate River basin
The study area is located on the Atlantic coast of Andalusia (SW Spain). Specifically, it is in the province of Cadiz The climate context is Mediterranean with Atlantic influence. The average annual precipitation is close to 800 mm/year, the average annual temperature is approximately 18 C, the potential and real evapotranspiration is about 1,110 and 585 mm/year, respectively. On the other hand, the wind is a very characteristic feature of the studied area. The most frequent are the West (Poniente) winds and East (Levante) winds. Poniente winds are moist, fresh and

Water resources problems of the Barbate River basin
The Barbate River basin presents some specific characteristics that affect the management and exploitation of the water resources: 1. In accordance with the current Hydrological Plan, all groundwater bodies in the basin are classified as being in a bad quantitative state. On the one hand, the piezometric records reflect a temporally descending and prolonged evolution. On the other hand, the index of exploitation (volume extracted/available resources) of the GWB is higher than that established as normative (BOE ). In addition, contaminants, mainly nitrates, are present in concentrations higher than recommended.
For this reason, the Barbate River basin is also classified as being in a bad qualitative state. In the Barbate River basin, the WEI is higher than 40% (Table 1).
In addition, of the estimated superficial contributions

Data collection
For the characterization of the hydrological system of the Barbate River basin, a determination and description of the components and the surface water and groundwater resources, the current and future demands, and the existing hydraulics infrastructures are needed. Therefore, through in situ recognition of the basin, extensive databases related to the management of water resources have been obtained.
The historical series of the main variables of the three reservoirs of the basin (water inflows, precipitation, water level, water storage, total discharge, discharge for irrigation, in the study basin or in its vicinity, whose data have been analysed.

Checking evaporation values
Due to the importance of the evaporation in the system, these values have been particularly important to verify.  (Figure 4), with a discrepancy in its average values of less than 2%. where ET o is the volume of water that has undergone evapotranspiration (mm/day), γ* and γ are psychrometric constants (mbar/C), e s is vapour pressure with air temperature (mb), e a is vapour pressure with dew temperature (mb), L is volumetric latent heat of vaporization (cal/gr), Δ is rate of change of saturation specific humidity with air temperature (mbar/ C), R n is net irradiance (cal/(cm 2 day), T average temperature ( C) and G is ground heat flux (cal/cm 2 ). For this purpose, the program uses the following objective function (Equation (2)):

AQUATOOL decision support system shell
where every term is an objective function corresponding to each one of the possible elements in the systemreservoir (E), river (R1-R5), demands (DC), artificial recharge (RA), pumping (BA) and others. All these objective functions are subject to constraints related to hydraulic principles (mass conservation) and to the physical limits of transport and conduction, reservoir capacities, etc.
Since this study is an important element of the water budget, for the quantification of losses by evaporation in reservoirs, SIMGES performs the calculations on a monthly scale and applies the following formula (Equation (3)): where S f and S i are the surface area (in ha) of the reservoir sheet corresponding to the final and initial volume, and e is the evaporation rate in mm.

Calibration and validation
Traditional methods (

Analysis of scenarios
The possible management alternatives and the needs of the system were studied to determine the optimal management strategy that could be implemented without high costs and with the fewest possible environmental effects. In this study, five possible strategies of action have been proposed: (i) conjunctive management of the reservoirs, (ii) conjunctive use of the surface-groundwater, (iii) transfer between reservoirs, (iv) artificial recharge of aquifers, and (v) combining the above strategies so they are compatible with each other. Different simulations within each strategy were carried out, with the management variables being modified.
Finally, the advantages and disadvantages of each strategy were analysed, with optimal management being developed and compared with the current management in the basin. A scheme of the proposed methodology is shown in Figure 6.  (Table 3).

DISCUSSION
After analysing the advantages and disadvantages of the simulations performed and the variable evaporation in the system, the most suitable management strategy for the Barbate River basin would be to implement a conjunctive use of surface water and groundwater and simultaneously  With this combined strategy, the reliability of the supply to all demands is 100%, the qualitative and quantitative state of the aquifers will improve, and the direct evaporation in the Barbate reservoir will be reduced.
Under the management strategy E5a (Figure 10, top), the agrarian demands could have been met with surface a reservoir with respect to the non-flooding situation is less than the absolute value of the losses (Témez ). The transfer to the atmosphere is also produced from the unflooded soil so that, in the rainy periods, the actual evapotranspiration and the potential practically coincide, regardless of whether the terrain is flooded or not.
However, in arid climates, or in the climates with periods of strong drought as the one that occupies us, the water shortage in the soil can become very high, which implies that the losses from a non-flooded surface are very close to zero, while the losses from the free sheet are maximum.    The selected management strategy (conjunctive use of surface water and groundwater plus transfer between reservoirs) shows better optimization of the resource. The key to this option is to store the resource during times of normal or elevated rainfall in the strategic reservoirs that suffer less evaporation (Celemín reservoir and aquifers) for availability during times of drought. In this sense, in just five years (1999)(2000)(2001)(2002)(2003)(2004)(2005), 34 hm 3 more (6.8 hm 3 /year) would have been available, which could have been used in the period of subsequent drought. In addition, the supply restrictions suffered in the area could have been delayed for at least one year, which in the southern part of Spain, which has a marked cyclicity in dry and humid periods, could be very relevant. The increase in the availability of resources may seem small for the whole basin, but it should be noted that, for groundwater users, that amount represents the difference between being classified as good or poor quantitative condition.
Finally, this study aims to contribute to the objectives of the 'Blueprint to safeguard Europe's water resources' (EC ) so that the results obtained here can be taken into account for the improvement of the knowledge of the Spanish basins, whose methodological guidelines for action are included in the 'Hydrologic Planning Instruction' (BOE ).