Methodology and objectives of the scenario formulation and evaluation

1       Objectives and Methodological background

Under this context, the analysis process is based on the concept of a “comprehensive scenarios” is used in the analysis process, which has been defined as combinations of:

1. A hydrological (availability) scenario and a demand scenario, which represent alternative future developments that are not affected by the decision-making process. These are not however sufficient to develop Water Management Scenarios that will satisfy the requirements of the Project, as they do not cover the issue of supply and demand-side interventions. For that purpose the third component that will allow the formulation of Comprehensive WM Scenarios, is

2. A selected water management option to be evaluated, one of a set of alternative supply or demand side management measures available.

Figure 1. Components of a Comprehensive Water Management Scenario

The interrelationships between the scenarios and water management measures can also be viewed through the DPSIR approach: the Water Availability scenarios represent the Drivers, the Demand Scenarios represent the Pressures, the State of the system is the Base Case state, and the management measures, which are the Responses, act on the whole system and redefine it (Figure 2).

The baseline scenario compared to which the alternative options were evaluated has been defined as the current state of the water system, including scheduled interventions as these are planned, under the assumptions that water availability and water demand will continue following the currently observed and forecasted trends. For the purposes of the WSM Case Studies, the scenarios were evaluated for a long time horizon, from 20 to 30 years, using the GIS-based Decision Support System that has been developed.

For each individual management measure, the behaviour of the water system was assessed and evaluated, in comparison to the baseline scenario.

The parametric analysis focused on the range of cost, effectiveness in demand coverage, and environmental sustainability of the system, expressed in terms of environmental costs. The performance of each of the management options applied was evaluated under different availability and demand conditions, and more specifically:

• a “worst case scenario”, combining low water availability and high demand,

• a “best case scenario”, combining high water availability and reduced demand, and

• a “business as usual scenario”.

In that way, it is possible after analysing the evaluation outcomes of all scenarios to select the options that are efficient in meeting the specific requirements of the case study. The performance of each option under a range of conditions is critical in defining the extent of their applicability.

The analysis of comprehensive scenarios was performed through the WaterStrategyMan Decision Support System, which was presented in detail in Newsletter 5.

Figure 2. The DPSIR system as a parallel to the strategy formulation process

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2         Formulation of Water Availability scenarios

Alternative availability scenarios are formulated through the Water Availability Module of the WSM DSS.

The Water Availability Module of the WSM Decision Support System aims at estimating the amount of water that is available in a water resource system, to be allocated to the existing demand use(r)s. Water sources considered in the WSM package currently comprise surface water, such as artificial or natural lakes and the river network system, and groundwater, renewable or not.

The main purpose of the applied water availability modelling is to generate forecasted monthly time series of available water for each water resource considered in the system. Time series output of the module concern natural recharge for renewable groundwater and surface runoff for reservoirs and river reaches. Two alternative methods can be applied for forecasting water availability and defining alternative scenarios:

1. By defining a set of customized years to be repeated in time, based upon the real observations at existing monitoring stations, and

2. By estimating runoff and natural recharge from a surface water balance performed on a monthly time step. 

In the second case, there are three ways to build scenarios for rainfall and temperature or evapotranspiration:

• repeating the base year as it is for the entire duration of the scenario,

• defining a total increment over the entire period, either annual or monthly, thus defining a yearly or monthly trend, or

• building up a sequence of previously created base years.

A stochastic option is also available; the idea consists in generating a certain number of forecast discharge time series based on a statistical analysis of historical discharge data series: the trend of historical data is kept in the forecast and fluctuations up and down the trend are produced in the generated series trying to maintain to the greatest extent the statistics of the historical fluctuations, such as mean, standard deviation and skewness. The user-defined number of discharge scenarios resulting from stochastic modelling, have to be all simulated by the water allocation model, and results have to be compared, thus leading to and permitting the analysis and classification of management options and strategies under uncertain conditions.

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3 Formulation of Water Demand scenarios

Similarly to Water Availability, the formulation of Water Demand scenarios is performed by the respective module of the WSM DSS. It should be noted that the analysis of water demand in the WSM DSS is strictly functional to the allocation of water resources.

The Water Demand Module generates hypothetical demand scenarios, which along with the availability scenarios constitute the basic and discriminating factor in the distribution of water from the sources to the users.

Within the water demand methodology, a specific formulation for scenario building has been adopted for each one of the different types of activity and water use, considered to be part of a water resource system. Those are:

• permanent and tourist population, representing the domestic use of water,

• farmers and breeders, needing water for land cultivation and animals,

• industries of various types, and

• non-consumptive uses, such as hydropower-generation, navigation and protection of aquatic life in rivers (environmental demand).

Scenarios are generated by specifying appropriate growth rates to the key variables (Drivers) that govern the water demand of the nodes, such as population for the domestic use, cultivable area and livestock for agricultural practices, production growth and energy requirements for industries and hydropower plants respectively.

Demand parameters that can be used to generate demand scenarios are summarised in Table 1.

The Month Variation variable represents the yearly distribution of the increment set by the user to the demand key variable.

Depending on the type of water availability model used, estimation of irrigation water requirements can be performed also in two ways, differing in complexity. A complex model allows for the calculation of crop water requirements according to the scenarios formulated for evapotranspiration (or temperature) using the crop coefficient model developed by FAO. A more simplified approach relies in the average monthly requirement of each type of cultivated crop, which does not vary over time.

Table 1. Attributes for building Demand Scenarios

Use/Requirement Type	Variables
Animal Breeding Site	Number of Animals
Industrial Site	Production
	Consumption Rate
	Share of Consumptive Demand
Irrigation Site	Maximum Cultivable Area
	Crop Area Share
Settlement	Residential & Tourist Population
	Population Month Variation (optional)
	Residential & Tourist Consumption Rate
Tourist Site	Tourist Population
	Month Variation (optional)
	Tourist Consumption Rate
Exporting	Demand
	Month Variation (optional)
Hydroelectricity	Energy Requirements
	Month Variation (optional)

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4 Management Options

In the process of the WSM project, a number of potential policy options and interventions have been identified for use in the management of water resources in arid and semi-arid regions. These were identified in the literature and through field work, and were modelled in the DSS following the development of suitable methodology, and have been summarized in Table 2, and are grouped under four categories:

1. Measures related with Supply Enhancement, introducing new structural interventions to increase water availability;

2. Measures of Demand Management, aiming to control and limit water demands; 

3. Regional Development measures, affecting the socio-economic preferences given to certain types of water use with respect to others and finally

4. Institutional policies, such as changing water pricing.

Instruments not available in the DSS can also be modelled through changes to the network structure or function (e.g. the introduction of cisterns in a settlement is modelled as a small reservoir with total capacity equal to that of the sum of the individual cisterns, set just outside the settlement).

Table 2. Management options identified for the Case Studies and modelled in the WSM DSS

Policy Option	Management option	Description
Supply Enhancement	Construction of surface storage reservoirs	Construction of water storage facilities that will be able to collect and hold water to be used later.
	Desalination unit construction	Construction of desalination units that will process sea or brackish water to produce drinking-quality water.
	Groundwater exploitation	Sustainable exploitation of underground aquifers through the drilling of new boreholes, pumping from existing boreholes and wells.
	Importing	Importing of water from nearby or remote areas by transporting it through any means or container possible such as pipelines, water barges etc.
	Water reuse	Transport of varying quality effluents for use to sectors where that quality is acceptable (e.g. treated wastewater used for irrigation of certain crops).
Demand Management	Conservation measures in household use	Application of water-saving devices and measures in the home, such as fitting flow-restrictors to faucets, insulating water pipes, outfitting garden hoses with shut-off nozzles etc.
	Introduction of new crop types	Substitution of existing crops with other crop species or varieties that have either lower irrigation requirements, or require irrigation during the less water-stressed season.
	Irrigation method improvement	This Action involves changes in irrigation practices in order to improve irrigation efficiency and reduce water losses (e.g. changing from flood to drip irrigation).
	Process change in industry	Implementation of changes in industry processes, in order to reduce the amounts of water required during processing and production (e.g. new processes, recycling etc).
	Quotas	Restriction of the amounts of water available per user, either directly through the allocation of a set volume to each user, or by limiting the duration of time that the water flow is available to users.
	Reduction of network losses	Repair and/or replacement of old networks in order to reduce the water losses that are a direct result of the network aging.
Social-Developmental Policy	Change in regional developmental policy	Implementation of changes in the regional developmental policy, such as shifting the local economy towards another sector that is less water-intensive. This is effected either through different priorities for the water sectors or through different growth rates.
Institutional Policies	Pricing	Control of the elastic water demand through the application of varying pricing levels.
	Environmental Policies	Penalties and fines, Impact and risk assessment.

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5 Evaluation of alternative options - Performance Matrix

The formulation and evaluation of a water management option, and consecutively that of a strategy, should evolve around and reflect the principles of Integrated Water Resources Management:

• Economic efficiency,

• Environmental sustainability, and

• Social equity.

Those principles are expressed through a set of goals that have to be achieved by a water resource system (Figure 3).

Figure 3. The goals of an IWRM strategy

The WSM DSS Evaluation

Evaluation of alternative water management instruments and strategies is performed using the WSM DSS package (Newsletter 5). Based on the primary objectives of a water management strategy (environmental compatibility, cost recovery of water services and coverage of demand for all sectors), a set of indicators is used that “measures” the performance of a strategy compared to those objectives. The selected indicators are outlined in Table 3.

Temporal aggregation of indicator time series is conducted according to a system performance approach suggested by ASCE.

The temporal aggregation involves the computation of a series of statistical criteria for the indicator time series based on the definition of a satisfactory range (upper and lower limit) of indicator values.

Those criteria are:

• Reliability,

• Resilience, and

• Vulnerability criteria, expressed through the Conditional Expected Extent, the Maximum Extent and the Duration of unsatisfactory values.

Criteria values are used to obtain an overall performance for each indicator incorporated in the analysis. The overall performance of a water management option or a strategy is obtained through multicriteria analysis, by assigning specific weights to each indicator.

Additional indicators that can be incorporated in the analysis concern the computation of indicators with respect to the total cost incurred by water uses and service, as the time series and present values of:

• Financial (Direct) costs,

• Resource costs,

• Environmental costs from pollution and (over) abstraction, and

• Benefits from water usage.

Table 3. Selected indicators for the evaluation of water management options and strategies in the WSM DSS Software Package

Category	Indicator
Environment Resources	Dependence on Inter-basin water transfer
	Desalination and reuse percentage
	Groundwater exploitation index
	Non-sustainable water production index
Efficiency	Demand coverage-Animal breeding
	Demand coverage-Domestic demand
	Demand coverage-Environmental demand
	Demand coverage-Hydropower demand
	Demand coverage-Industrial demand
	Demand coverage-Irrigation demand
Economics	Direct costs
	Resource costs
	Environmental costs
	Revenues
	Rate of cost recovery
	Benefit from water use

Evaluation in the Comprehensive Scenario context

No single instrument, as those examined in the scenario analysis, can address all of the goals mentioned above. However, each option should be evaluated against a set of indicators that at best can address such issues in order to formulate a set of candidate options that can achieve those targets during the next phases of the project.

Under this context and in order to achieve a meaningful overall evaluation for the options examined in the range of Case Studies, it is necessary to ensure comparability. For that purpose, a specific set of indicators has been selected for cross-Case Study comparison, and those are presented for each measure evaluated. The overall aim is to collectively score measures in order to rank those as to their general applicability and efficiency in arid and semi-arid regions.

For this purpose, a series of indicators was selected to be used for all Case Studies, based on the typology of regions outlined in the Introductory Section. Those are:

• Effectiveness vs time for irrigation and domestic water use, expressed as:

• Coverage of water demand

• % improvement of deficit with respect to each reference scenario

• Total direct cost for the provision of water services and the application of the different options, expressed in present value terms,

• Total environmental cost, incurred from pollution and (over)abstraction of surface and groundwater, expressed also in present value terms.

Those indicators are not comprehensive for all case studies involved in the Project and the list can be enhanced in order to include other indicators that are meaningful in the analysis of the case study areas.

However, they can be used to derive a Performance Matrix which permits to rank the options identified through stakeholder consultation, modeled and simulated in the WSM Decision Support System.

Following from the outcomes of the Comprehensive Scenario evaluation and ranking, the next stage is the formulation of strategies. This will involve the planning of combinations of management measures in the timeframe set, and re-evaluating the strategies in their entirety using the WSM DSS as previously done for each measure individually.

The ultimate goal is the ranking of the selected strategies for each Case Study and the selection of the best suited approaches.

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