The Year-2000 edition of the Wengen Workshops on Global Change Research, which is the 6th conference in the series since 1995, was held from September 27-29 in Wengen (Bernese Alps, Switzerland). One of its primary aims was to bring together physical and social scientists to discuss some of the critical issues related to water resources in the world and, especially, how these are likely to be modified in a changing global climate in the course of the 21st Century. Over 70 participants were present throughout the three-day meeting, representing 20 different nationalities. 

It is generally accepted today that a warming climate as projected by General Circulation Models will, in the course of coming decades enhance the hydrological cycle, which implies higher rates of evaporation, and a greater proportion of liquid precipitation with respect to solid precipitation. These physical mechanisms, associated with potential changes in precipitation amount and seasonality, will affect soil moisture, groundwater reserves, and the frequency of floods or droughts. Though water is present in water is present in ample quantity globally, supply is often limited regionally. The supply of water is limited and governed by the renewal processes associated with the global hydrological cycle. With the expansion of human settlements and the growth of industrial activities, water has been increasingly used in new ways, including for the assimilation and discharge of wastes. This resource has been taken for granted, and only in the past few decades has increasing water shortage and declining water quality from pollution drawn attention to the inherent fragility and scarcity of water. This has led to concerns about water availability to meet the requirements of the 21st century.

Because of increasing population and changing patterns of use, the additional demand will be accompanied by a sharp decline in water availability per capita. While a consumption of 1,000 m3 of water per year and per capita is considered a standard for «well-being» in the industrialized world, projections of annual water availability per capita by the 2020 for North Africa are 210 m3, 700 m3 for Central Asia, and 1,100 m3 for southern Asia. This trend is declining in all parts of the world, including those that are considered to have ample water resources. 

Water resources will come under increasing pressure under conditions of global change. Significant changes in environmental conditions such as climate, land-use and other factors, will affect demand, supply and water quality. In regions which are currently sensitive to water stress (arid and semi-arid regions), any shortfalls in water supply will enhance competition for water use for a wide range of economic, social, and environmental applications. In the future, such competition will be sharpened as a result of larger populations, which will lead to heightened demand for irrigation and perhaps also for industrial activities, at the expense of drinking water. Disputes over water resources may well be a significant social consequence in an environment degraded by pollution and stressed by climatic change.

Against the backdrop of physical and socio-economic problems, the Workshop program was divided into 5 separate sessions, namely:

1. Sensitivity of precipitation regimes to climatic change : observations and models
2: Floods and droughts : past, present and future
3: Sensitivity of precipitation and runoff to climatic signals such as the NAO
4: Climate projections and hydrological assessments
5: Water resource management : property rights, conflicts, transboundary sharing

In addition, a full-day session was organized under the auspices of the International Geosphere-Biosphere Program (IGBP); this special session was coordinated by the IGBP-BAHC (Biological Aspects of the Hydrological Cycle) program, coordinated by the Potsdam Institute for Climate Impacts Research (PIK), Germany.

Session 1 addressed the problems and approaches allowing the use of climate information at scales typical of General Circulation Models (GCMs) at catchment or finer scales. The most commonly-adopted methods today include statistical downscaling, by which large-scale synoptic climate fields are correlated to changes in local and regional climate characteristics, and dynamical downscaling. This is a physically-based method and is thus more robust to climate change than the statistical approaches, but there is an essential need to undertake computationally-intensive multiple and multi-year simulations in order to separate noise in the system from the climate change signal. Several contributing papers focused on case studies using Regional Climate Models (RCMs) linked to hydrological models, applied to the analysis of runoff under conditions of convective activity and extreme precipitation, in regions of complex topography, or stakeholder-driven investigations such as water runoff simulations in Quebec undertaken for a major utility. Thorough analyses of GCM results for the 20th Century were reported at the Workshop, in order to illustrate the improvements in model results which have taken place in recent years, and the increasing confidence with which the models can be used for projecting climatic change in coming decades. However, there is still much room for improvement; there is also a need to address more fully the manner in which climate and impacts models (e.g., hydrological models) can be linked, in terms of consistency and the overlap between different scales, the underlying physical assumptions, and the parameterizations used.

Session 2 was devoted to the two extremes of water resources, namely floods and droughts, the focus here being to identify the climate change component in river floods. These have significant economic implications, as was shown by several scientists from Western and Central Europe. Many long time series have been studied worldwide with the aim of detection of nonstationarities, yet there is no conclusive evidence of climate-related changes in flow records, in general. Even if baseline data (with no substantial human impact) are available, detection of weak (if any) climate-related change amidst strong natural noise is very difficult. Estimation of future changes of flood risk, due to climate change, is possible in qualitative terms only. Many studies presented here point to the probable increase in precipitation and runoff in Europe, although southern and central Europe may expect extended dry periods, particularly during summer months. Droughts can occur in all regions, even those which are not commonly associated with such extremes. For example, a case study for Swiss forests was shown, illustrating the results from a forest/hydrological model pointing to regions of increasing drought stress on trees; this stress is a complex interaction between climatic, edaphic, and biological factors. In all the talks of this session, it was emphasized that there is a need for climatological data of high quality, both from the observational point of view as well as from future climate projections. In this respect, the point was raised that access to hydrological and climatological data is very often a problem, especially in Central and Eastern Europe and in the developing world, which have considerable difficulties in finding the funds for accessing data when these are not freely available. A further point of interest is the increasing public perception that extreme events are a direct consequence of global warming as, for example, the devastating 1997 floods in Germany, Poland and the Czech Republic. This is an issue which brings to the forefront the need to communicate uncertainty and the fact that, at present, no statistically-meaningful cause-to-effect relationship can be made.

Session 3 provided an overview of the links between strong decadal-scale climatic fluctuations such as the North Atlantic Oscillation (NAO) or the El-Niño/Southern Oscillation (ENSO) on precipitation regimes and river discharges. Several case studies were presented here, such as the sensitivity of precipitation variations in the Canary Islands and Morocco (regions which are close to the centers of action of the NAO), summer moisture patterns in Romania and Eastern Europe, and river discharges in Central Europe to changes in the NAO. For example, a strong shift occurs in the maximum discharge of the Vistula River in Poland during periods when the NAO index (the surface pressure difference between the Azores High and the Iceland Low) is high (approx. 3,000 m3/s) compared to periods when the NAO index is low (approx. 4,700 m3/s). High NAO values are associated with strong zonal flow over the North Atlantic and storm tracks which cross Europe at more northerly latitudes than when the NAO index is low.

Session 4 addressed hydrological assessments for the future, and the requirements in terms of climate projections and other data. The problem of scale is a dominant feature of such assessments, in that it is necessary to link GCM data to hydrological models, as was mentioned in the overview presentations of Session 1. In several examples given in Session 4, advanced multiple "cascade" methods (i.e., the processes linking models at one scale to those at a finer scale) have sought to couple global to regional climate models, and on down to hydrological models at the very fine spatial scales. Further down the "cascade" sequence, one study made use of a crop model to assess the potential change in the agricultural output of the Elbe River basin in response to changing conditions of hydrological stress. All presentations in this session emphasized the uncertainties involved in applying the methodologies developed; these are related to each step in the cascade process, whereby errors transferred from one model may amplify or contaminate results of the model at finer scales. It was shown in many of the studies that changes in extremes yield the greatest uncertainties.

Session 5 contained a number of cross-cutting themes, which were also taken up in the special IGBP/IHDP/International Programs session. Much of the genuinely interdisciplinary work was presented here, as opposed to the other four sessions, essentially devoted to sectoral and technical issues. Session 5 and the special session addressed a number of important topics, in particular:

Vulnerability of water resources
Vulnerability assessments of water resources integrate multiple interacting stresses and feedbacks from climate change, climate variability and direct effects of human activities, such as changes in land and water use, changes in distribution and age-profiles of populations, changes in economic activities and settlement patterns, and changes in political environments. There is a strong human dimensions component in vulnerability assessments. Exposure to environmental stresses and reaction to such exposure are major factors, but also very important is the potential for adaptation, which is essentially region-specific. This was demonstrated for losses due to extreme flood events, where developing countries sometimes suffer severe loss of life, while losses in developed countries are mostly economic. A goal of integrated water resource management is to reduce vulnerabilities.

Integrated research now has quite a number of tools at its disposal, such as coupled models, use of remote sensing data, exchange of data between different research components, etc. The full integration of human dimensions was seen to be essential to water research, e.g., for understanding the driving forces underlying change, including behavioral and institutional aspects.

Uncertainty is an inherent component for climate simulations and downscaling techniques, as well as climate variability and runoff analyses. There exist parallel uncertainties about the evolution of economic growth and changes in preferences. These uncertainties are then introduced into various predictive and impacts models and hence into water management applications, such as design and operation of dams, adaptation of agriculture, and allocation of water for economic sectors. Similarly, projections of future water use as well as economic assessments, e.g., of damage and adaptation costs of changing water availability, have considerable uncertainty built into them.

Although research has the ultimate aim of reducing uncertainty, there is a need to communicate existing uncertainty beyond the scientific community. Communication between scientists, the general public, policy makers, water resource managers and further participation of stakeholders is essential throughout all phases of research, including from the beginning of research planning in order to define relevant research questions, and also later on in order to apply research results, in particular to water resources management. Communication should make uncertainties part of the knowledge base for decision making. A number of ways were identified for communicating uncertainties, such as scenarios and alternatives for decision makers, results of risk assessments (to be performed jointly with stakeholders) and probabilities of exceeding critical thresholds, whereby stakeholders must be included in the definition of these critical thresholds.

Extreme events
Extreme events such as droughts and floods may well become the dominating effects of climate change in water resources. Currently a trend of increasing economic losses due to extreme flood events is observed. It is not clear at this stage, whether there is an underlying trend in frequency and intensity of extreme flood events and if this may be attributed to climate change, or whether there is only an increase in exposed economic value. Hence a systematic and comprehensive database of past flood events is required. This is an area for collaboration with the private sector, in particular insurance and re-insurance companies.

Groundwater and surface waters are common-pool or shared resources, often shared by more than one nation. This raises the question of who owns the water, of access and of property rights. Furthermore, water is often viewed as a strategic resource (for water supply, for food production, and for energy and industrial use), and hence economic and scientific arguments may only play a minor role in decision making. Property rights are often ill-defined for common pool resources or manifest very unequal access rights. Moreover, existing agreements on property rights and water resource planning often do not take into account climate and hydrological variability / trends. There is consequently the potential for conflict over shared water resources. Presentations were made in this sense, focusing on the Tigris-Euphrates conflict between Turkey and Syria, and the Jordan River Basin resources shared between Israel and its Arab neighbors. The need to achieve cooperative solutions was stressed, in order to maximize the joint benefit of resource use ("win-win strategies"). Unequal water use can be a fundamental cause for conflict between countries or between regions within countries. These agreements should be established proactively, and not in response to emergency situations. Cost efficient solutions, that also incorporate equity issues, may increasingly involve the private sector in water supply and management.

Regional studies
A number of integrated regional studies are now underway for various river basins in different parts of the world. Changes in land and water use are generally recognized to be of more immediate and direct relevance to water resources than changes or variability in climate. As a general principle, changes in runoff are much stronger than the underlying changes in precipitation, because of complex interactions at and beneath the surface, as well as direct human factors which interact with the natural system. Furthermore, teleconnections are increasingly found between changes in land and water use in one region, and effects upon water resources in another region, sometimes spanning several countries. The links are generated mostly through atmospheric or river transport processes.

A final plenary session addressed the future needs of the scientific community to help address the issues raised and discussed at the Wengen-2000 Workshop. Among the most pressing points, the participants identified the following:

Better focus on the vulnerability of systems
Need to live with uncertainty, but improve its analysis and communication. Emphasize the aspects which are known today with a reasonable degree of confidence, such as the agreement on the sign of change in many regions as projected by climate models
Refine the problems of scaling requirements, from the global to the local scales
Convergence of approaches between the climate/hydrological sciences and the social and economic sciences, e.g., aggregation of individual decision making in social sciences, downscaling vs upscaling, feedback mechanisms. Steps towards genuine integration.
Inventory of existing regional studies on floods and drought for past, present and future climate
Address the problem of signal to noise ratio in the future, i.e., climate variability vs climatic change

It was further suggested that:

less well studied regions should, where possible, benefit from transfer of results (example: urban-rural coupling);
results from regional studies could be used in global assessments of water resources, including the identification of particularly vulnerable and critical regions in the future

The participants expressed interest in the idea of a follow-up Workshop, perhaps in 2005, in order to monitor progress which has been made on these issues in the intervening 5-year period.

The sponsorship of the following organizations is gratefully acknowledged:

University of Fribourg, Switzerland
University Institute Kurt Boesch, Sion, Switzerland
Swiss National Climate Program, Bern, Switzerland
Swiss National Science Foundation, Bern, Switzerland
International Human Dimensions Program, Bonn, Germany
International Geosphere-Biosphere Program / BAHC, Potsdam, Germany
European Forum for Integrated Environmental Assessment, Amsterdam, The Netherlands

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    Franziska Keller, last update, 05.01