JAN-MAR 2004


 Indicators and Indices for decision making in water resources management

1         The need for indicators

Indicators are a tool to describe the economic, environmental, social and/or institutional conditions of a system, i.e. a country, region, community, etc. Examples of indicators are the well-known and frequently used economic indicators gross domestic product (GDP) and gross national product (GNP).

Indicators are instruments of simplification as they summarise large amounts of measurements to a simple and understandable form in order to highlight the main characteristics of a system. Information is reduced to its elements, maintaining the crucial meaning for the questions under consideration.

On the other hand, the aggregation causes a loss of information, but if the indicator is planned properly, the lost information will not gravely deform the result. The figure below shows the different levels of aggregation. The primary data, that are simple measurements, is analysed and combined to indicators, e.g. the crime rate in a region or life expectancy at birth. These are formed to a subindex, also called transformed indicator, for each issue in order to convert them to a dimensionless range, typically from 0 to 1 or from 0 to 100, and then aggregated to an overall index consisting of a single number. Indices include all aspects that are significant for the question under consideration, such as economic, social and environmental issues. Clearly, the application of indicators and indices is constrained by data availability. 

Information pyramid (Wamsley, 2002, modified)


The following criteria for selecting indicators should apply:
  • Direct relevance to project objectives,
  • Limitation in number,
  • Clarity of design,
  • Realistic collection or development costs,
  • Clear cause and effect links,
  • High quality and reliability,
  • Appropriate spatial and temporal scales,
  • Targets and baselines,
  • Little or no interrelation.

Indicators have typically different units, e.g. GDP in US$ or water demand in cubic metres per person. In order to facilitate an aggregation of these indicators, they have to be transformed to a dimensionless scale, typically to a range between 0 and 1.

2         Existing Indicators in Water Management

Frequently used indicators and indices

Probably the most frequently applied indicator is the Falkenmark Water Stress Indicator, that simply relates the available water resources in a given region (or country) per year to the number of inhabitants, regardless of to the temporal and spatial distribution of the water resources.

Water availability of more than 1,700 m³/capita/year is defined as the threshold below which water shortage occurs only irregularly or locally. Below this level, water scarcity arises in different levels of severity. Below 1,700 m³/capita/year water stress appears regularly, below 1,000 m³/capita/year water scarcity is a limitation to economic development and human health and well-being, and below 500 m³/capita/year water availability is a main constraint to life. More details and actual values for a number of countries are given in the Appendix.

If the temporal and spatial distribution is considered (e.g. in regions with a pronounced seasonal rainfall pattern), the Dry season flow index (Water Resources Institute WRI) can be applied. This indicator is calculated by dividing the volume of runoff during the dry season, i.e. during the four consecutive months with the lowest cumulative runoff, by the population. Based on the Falkenmark definition, a basin is water stressed if less than 1,700 m³/year/person is available, and amounts between 1,700 m³/year/person and 4,000 m³/year/person indicate adequate supply of water.

Another indicator that reflects the variabiltiy of water resources is the Water availability index WAI which includes surface water as well as groundwater resources, and compares the total amount to the demands of all sectors, i.e. domestic, industrial and agricultural demands. The month with the maximum deficit or minimum surplus respectively is decisive.

The Basic Human Needs Index (Gleick, 1996) considers the use of water instead of water availability. It is based on the assumption that a person needs 50 litres per day for basic water requirements (BWR), such as drinking, cooking, bathing, sanitation and hygiene.

An indicator that combines information about water abstractions and water availability is the index of water scarcity. It is defined by the intensity of use of water resources, i.e. the gross freshwater abstractions as percentage of the total renewable water resources or as percentage of internal water resources.

Heap et al. (1998) added the variable of desalinated water resources to this indicator as the share of desalinated water is very significant in some regions.

More complex indices that are based on the aggregation of sub-indices and indicators include the Vulnerability of Water Systems (Gleick, 1990) that is based on indicators in five criteria, and the Environmental Sustainability Index (ESI) that measures overall progress towards environmental sustainability in five core components (World Economic Forum, 2002).

Recently, the Water Poverty Index (WPI) (Sullivan, 2002, Lawrence et al., 2002), developed by the Centre for Ecology and Hydrology (CEH), has been intensively discussed. This index tries to show the connection between water scarcity issues and socio-economic aspects. It ranks countries according to the provision of water, combining five components (Resources, Access, Use, Capacity and Environment).

Data requirements, scales of application and references for various water-related indicators and indices are summarised in the Appendix.

Classification of Indicators

There exist a number of different approaches for structuring indicators in a way that the structure reflects indicators describing the condition of a system and indicators describing the response of the system to a given condition.

A widely used approach to structure indicators is Pressure-State-Response (P-S-R) approach that was first introduced by OECD in 1994 and can be applied at the national, sectoral, community, or individual firm level. It is based on the assumption that human activities exert a pressure on the environment and thereby affect the quality and quantity of the natural resources (its state). The pressures, in turn, cause a response of the society that can be through environmental, economic and sectoral policies. Pressures cover both direct and indirect pressures. Direct pressures exert from the use of a resource or a discharge of pollutants, whereas indirect pressures result from the activity itself or from trends of environmental significance. The construction of a new port has direct impacts by displacing natural areas and may have indirect impacts by increased traffic and hence pollution.

The original concept of the P-S-R approach has experienced some modifications and adjustments; examples are the Driving force-State-Response (DSR) model that was formerly used by UNCSD or the Driving Forces-Pressure-State-Impact-Response (DPSIR) model that is used the European Environment Agency (EEA).

It can be used as a basis for a framework to identify and develop indicators for Integrated Water Resources Management on a regional scale. The DPSIR framework identifies cause – effect relationships and allows for the separation of categories of issues and provides flexibility for usage and analysis. The DPSIR categories are defined as follows:

Driving force indicators reflect pressures exerted by natural phenomena and anthropogenic activities that, in general, cannot be easily manipulated but provide essential information to understand the regional context. Pressure indicators reflect the pressures exerted on water resources and the water use groups of a region, as a result of the driving forces. State indicators assess the current status of water resource. Impact indicators assess the effect that a pressure has on the state of user groups and resources and Responses relate to the social response via policies, laws, measures etc.

Classification schemes

This section is aimed at presenting approaches of developing set of environmental and water-related indicators and indices.

In 1996, the Commission on Sustainable Development of the United Nations (UNCSD) published a working list of indicators on Sustainable Development that are structured according to the Driving Force-State-Response model.

The list follows the chapters of agenda 21 and can be seen a flexible list from which countries can choose indicators according to their priorities and targets. The indicators cover social, economic, environmental and institutional aspects of sustainable development and mostly refer to a national or country level.

The Organisation for Economic Co-operation and Development (OECD) has developed a set of more than 200 indicators that measure environmental performance and progress towards sustainable development. The indicators are organised by issues including climate change, air pollution, biodiversity, waste and water resources and structured according to the PSR model. The OECD work focuses primarily on indicators to be used on national and international level. The water related core indicators are subdivided into freshwater quality indicators and indicators for water resources.

The European System of Environmental Pressure Indices (EPI) has been developed in order to describe human activities that have a negative impact on the environment in the European Union. 48 indicators were defined structured according to the DPSIR-approach, including several connected to water. The Environmental Sustainability Index (ESI) measures overall progress towards environmental sustainability in five core components and comprised a total number of 69 environmentally related indicators.

The Mediterranean Commission on Sustainable Development (MCSD) has the target to provide a tool to measure progress to sustainable development in the Mediterranean countries. For that reason, a set of 130 indicators structured according to the PSR-approach was developed by its activity centre called “Plan Bleu pour l'environnement et le développement en Méditerranée” (Blue Plan for the Environment and Development in the Mediterranean), 40 among them were adopted from the UNCSD working list of indicators.

The Water Framework Directive (WFD) established a framework for the protection of inland surface waters, transitional waters, coastal waters and groundwater. 

The WFD classification methodology approaches water resources from an environmental perspective, and determines different levels of classification of water bodies, from the microlevel determination of chemical and biological indicators, to the determination of the quality status of entire bodies, to establishing macroscale ecoregions.

This Directive, under Article 8 which establishes “Monitoring of surface water status, groundwater status and protected areas” proposes a comprehensive set of indicators for assessing the quality of waters, as well as a series of standards and measures for the protection and improvement of the quality of waters. These measures are described in Annex V of the directive. The status of water bodies is determined, based on these indicators, to be improved or maintained accordingly.

Regarding Groundwater, the quantitative and chemical status of the resource is monitored. The parameter for the classification of quantitative status is the groundwater level regime. The core parameters for the determination of groundwater chemical status are: oxygen content, pH value, conductivity, nitrate and ammonium. The quality elements for the classification of ecological status of Rivers, Lakes, Transitional waters, Coastal waters, and Artificial and heavily modified surface water bodies involve monitoring of parameters indicative of biological quality elements, parameters indicative of hydromorphological quality elements, parameters indicative of all general physico-chemical quality elements, thermal conditions, oxygenation conditions, salinity, acidification status, nutrient conditions, transparency, and the priority list substances. For transitional and coastal waters, the tidal regime is additionally considered.

Article 6 of the WFD establishes a “Register of protected areas”, which according to Annex IV of the directive include areas designated for the abstraction of water intended for human consumption, areas designated for the protection of economically significant aquatic species, bodies of water designated as recreational waters, including areas designated as bathing waters, nutrient-sensitive areas, including areas designated as vulnerable zones,areas designated for the protection of habitats or species where the maintenance or improvement of the status of water is an important factor in their protection, including relevant Natura 2000 sites.

Finally, in Annex XI the WFD also presents a set of ecoregions in the European Union, for rivers and lakes, and for transitional and coastal waters.

3         The WSM-DSS Approach

As the general idea of the decision support system (DSS) that has been developed is to compare the performance of different water management strategies over a sufficiently long period of time, the evaluation approach that is implemented in the Decision Support System (DSS) of the WaterStrategyMan is based on a two step procedure.

The first step involves a temporal aggregation of time series of aggregation into single values, the second step is aimed at providing time series of indicators as additional information to the decision maker.

Temporally aggregated values

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.

A temporal aggregation is done according to a system performance approach suggested by the American Society of Civil Engineers (ASCE) that is aimed at temporally aggregated time series of performance indicators of a system. For each of the indicators used in the WSM-DSS, the following values are computed:

  • Average value.
  • Reliability. Reliability is the probability that a criterion value will be with the predefined range of satisfactory values.
  • Resilience. Resilience is an indicator for the speed of recovery of an unsatisfactory condition. It is defined the number of times a satisfactory value follows an unsatisfactory value related to the total number of values.
  • Max. Extent.
  • Duration.

For the evaluation of a given strategy, an overall score is computed using the temporally aggregated criterion values. Weights can be assigned to indicator values to reflect the preference structure of the decision-maker. The aggregation of all indicators mentioned above results in a score for any given strategy so that a ranking of those strategies can directly be obtained.

Time series of indicators

In addition to the indicators and indices that are directly used for the evaluation of water management strategies, the DSS provide a number of additional time series of indicators and indices based on the primary data that is either modelled by the system or entered as initial data. Their purpose is merely to provide the user with additional information on the evaluation process.

Appendix contents:

Glossary of terms and definitions
Falkenmark Water Stress Indicator (Resources to population index)
Dry season flow by river basin
Water availability index WAI
Basic Human Needs Index
Index of water scarcity
Vulnerability of Water Systems
Environmental Sustainability Index (ESI)
Water Poverty Index (WPI)
Water resources indicators, applicable scales and data requirements
PSR Approach
DPSIR Approach
CSD Working List of Indicators of Sustainable Development
OECD environmental indicators
European System of Environmental Pressure Indices (EPI)
Plan Bleu
WFD Classification
The WSM - DSS Approach
Web Links for further reading