Figure 1. Estimated fluxes and storage components of the global hydrological cycle between 1979-2000. (after Trenberth et al., 2007)
of a natural cycle) versus that of the manage-ment (and consumption) of a limited and fi-nite resource. In this context irrigation means using “blue water” to increase the availability of “green water” to be transpired through and stored in crops. Even if we speak about water consumption this means only a temporary de-viation and retardation of water to participate in the global hydrological cycle. Ultimately all water, even if physically consumed and stored, in the tissues of living organisms, returns to this cycle, though frequently in deteriorated quality state and geographically at different locations.
While the terminology “green water” and “blue water” has found its way into the scientific dis-course as proven also in this book, this “color coding” is not without certain potential of misunderstanding. Even in this book a paper mentions the “blue drop” and “green drop” ini-tiatives describing monitoring of water supply and sanitation development in South Africa re-spectively. Furthermore the original meaning of “blue water” in the English language is deep waters, the open sea.
As a potential alternative for a scientific no-menclature for “blue water” and “green water”
respectively the editors suggest to distinguish between waters in the terrestrial part of the hydrological cycle of which the movement is governed overwhelmingly by molecular forces (“green water”) opposite to those gov-erned principally by gravitational forces (“blue water”).
References
Ů Trenberth K.E., L. Smith, T. Quian, A. Dai, J.
Fasullo, 2007. Estimates of the global water budget and its annual cycle using obser-vational and model data. J Hydrometeor 8, 758-769.
Ů Hoekstra, A.Y., Chapagain, A.K., Aldaya, M.M., Mekonnen, M.M., 2011. The water footprint assessment manual: Setting the global standard, Earthscan, London, UK.
Whether the matter is water scarcity, flood risk, water availability or sustainable development, there is considerable need to support politi-cal decisions and resource management with easy-to-use information describing the state of the system, the efficiency and effectiveness of planned and implemented projects. This description would be very complicated unless we resort to indicators characterizing the com-plexities of reality with a few selected features and corresponding metrics. We need to know whether we are on the right track or whether the assessed status quo necessitates interven-tions. Measuring does not automatically mean
‘numerical quantification’ but common scales and a common terminology are needed to facil-itate dialogue within the disciplines of the pro-fessional community and the communication with the public, the media and policy makers.
The problem is not only how to use simplified scales to measure, but also how to select those indicators which are facilitating communica-tion. These problems are not unique for water resources management. Data scarcity and rep-resentativeness forms one group of problems.
Simplification and selection of specific indica-tors without distorting the complex truth is another.
The basic dilemmas associated with indica-tors will be highlighted using the example of sustainability indicators. Singh, Murty, Gupta and Dikshit (2009) published for example an overview of sustainability assessment meth-odologies. In an excellent, however unavoid-ably eclectic study they introduce, and partially compare 70 sustainability indices classified into 12 categories. Indices are usually aggregates of scores of individual and composite indicators.
Among those 41 summarized in a comparative table, indices like the ‘Well being index’ (WBI) with 87 or the ‘Environmental Sustainability In-dex’ (ESI) with 68 sub-indicators seem to be the most complex ones. While both appear to be quite complex and comprehensive, they differ considerably. ESI uses equal weights to calcu-late the arithmetic average of these subcom-ponents while WBI uses subjective weights to calculate the weighted average.
This type of ‘super indices’ which aggregate cores of simpler indicators depend excessively on factors like data availability and reliability on the global scale to measure and compare so many dimensions of what might be called sustainability. It is however clear that indices, through being chosen, could and usually do include value judgement. Using weights,
as-Indicators and their limitations
Figure 1. Framework of Measuring Sustainability used by UNCSD 2001
signed to individual indicators or even the selection which aspect should be considered are examples of this inherent value judgement.
There is nothing wrong with it but this subjec-tive component has to be acknowledged. Be-yond this feature which can only be overcome by broad-based consensus, it is obvious that an aggregate of 60 or 80 indicators hardly yields an easily understandable metric. But can the multidimensional assessment of sustainability be avoided? Compromise concepts tend to settle on a 4-dimensional assessment like rec-ommended by United Nations Commission on Sustainable Development, UNCSD (2001) with-in the four “mawith-in dimensions” of sustawith-inability.
Measuring the social, environmental, economic and institutional dimensions needs additional categories which could (and probably should) be considered. Figure 2 shows 15 possible and frequently used subcategories.
These subcategories are not exhaustive and each of them could be measured with many indicators. Consequently, such kind of frame-works may not ensure the required simplicity either.
Just to juxtapose this easily escalating trend, one of the indices also used and presented in the context of sustainability is the Human De-velopment Index (HDI).
Measuring only 3 dimensions like
Ů the environmental dimension: with the indicator ‘life expectancy at birth’;
Ů the social dimension: with adult literacy rate (2/3 weight) and aggregated primary, secondary, tertiary school enrolment ratio (1/3 weight) and the
Ů economic dimension: GDP/head in pur-chasing power parity (PPP) US$ the HDI is hardly comprehensive enough to measure sustainability, yet being calculated and published annually at country level since several years it has assumed the role of an Olympics-like competition.
Admittedly, measuring sustainability is prob-ably the most complex task. However develop-ing water resources and/or water management and governance indicators is not an easy task either. While core physical characteristics like annual renewable water resources (over a refer-ence area) may seem a robust indicator much depends on the choice of the resolution. Figure 2 displays the Americas. In a relative scale the water scarcity is shown for a fine pixel-based resolution. Worth to compare this detailed in-formation with the global distribution of the renewable annual water resources per capita as published by the first World Water Develop-ment Report (WWDR I) in 2003 (Figure 3)..
The country-based resolution completely hides large discrepancies which may exist even within water rich countries like the US, Canada, Brazil etc.
Similar discrepancies can be shown in case of the water use within the so-called Falkenmark index (Falkenmark, 1995), assigning countries
Figure 2. Water scarcity in the Americas (Courtesy of C.J. Vörösmarty)
Figure 3 Annual renewable water resources per capita (country based) Source: WWDR I
into scarcity, water stress, vulnerable or normal classes depending on their annual renewable water resource per capita. 1000; 1700; 2500 m³/
capita and year are set as upper limits for the scarce, stress and vulnerable country classes re-spectively. Figure4 shows a number of African countries and the widely varying water avail-ability in the continent. The two bars indicate the dramatic decrease of the value of the index between 1990 and 2025 due alone to increas-ing population. Climate change may induce additional lowering, but Figure 4 documents that the overwhelming component of (future) water stress is related to demographics. In addi-tion, black arrows indicate the positions of
Chi-na (CHI), Germany (DEU) and the Central Asian Republics (CAR), as well the Ruhr river basin, a highly industrialized river basin in Germany.
This index, which served and still serves as basis to make the world aware of water problems has the drawback that neither within year vari-ability of seasonal differences, nor the available technical, infrastructure and other means of water resources management are considered.
This explains why a densely populated basin in the moderate climate of Western Europe would be classified as a very water scarce area.
Besides fairly uniform distribution of water re-sources within the year the Ruhr basin has
sev-eral upstream reservoirs and multi stakeholder based water resources management services.
The dilemma of water resources indicators and developing indicators altogether has been highlighted by the preceding examples.
The need for a “policy relevant compromise” is obvious. As far as integrated water resources management or the assessment of water re-sources for human use but also for ecosystem services are concerned a single dimension (like renewable water resources per year and head) is clearly dissatisfactory. The compromise solu-tion was proposed by the Task Force on Indi-cators, Monitoring and Reporting of UN Water
which suggested in 2009 a set of 15 indicators, classed into four categories: context, function-ing, governance and performance.
A further major issue to be debated is, whether indicators are needed for hydrological units like river basins or for jurisdictional entities like countries. Actually both types of information are needed. Discrepancies can be huge as Fig-ure 2 (country versus pixel scale resolution) and Figure 4 (Germany versus the embedded Ruhr basin) indicate. As most of the water resources management investments are public funding and the ultimate decision making is usually following the sovereignty lines, country-based indicators remain essential. The inherent uncer-tainties and potential pitfalls notwithstanding the need for indicators and aggregate indices is likely to increase. Thus indicator development and testing will remain an important research area.
Figure 3. Annual renewable water resources per capita (country based) Source: WWDR I
References
Ů Falkenmark, M., 1995. Coping with water scarcity under rapid population growth.
Conference of SADC Ministers, Pretoria, 23-24 November 1995
Ů Singh, R.K., Murty, H.R., Gupta, S.K., Dikshit, A.K., 2009. An Overview of Sustainability Assessment Methodologies. Ecological Indicators 9, pp. 189-212, Elsevier.
Ů UNCSD, 2001. Indicators of Sustainable Development: Framework and Method-ologies. Background Paper No. 3, Ninth Session 16 - 27 April 2001, New York.
URL: http://www.un.org/esa/sustdev/csd/
csd9_indi_bp3.pdf
Ů http://www.unwater.org/Indicators.html Figure 4. Availability of annual renewable water per capita (country based)