Executive Summary

Extreme impacts can result from extreme weather and climate events, but can also occur without extreme events. This chapter examines two broad categories of impacts on human and ecological systems, both of which are influenced by changes in climate, vulnerability, and exposure: first, the chapter primarily focuses on impacts that result from extreme weather and climate events, and second, it also considers extreme impacts that are triggered by less-than-extreme weather or climate events. These two categories of impacts are examined across sectors, systems, and regions. Extreme events can have positive as well as negative impacts on ecosystems and human activities.

Economic losses from weather- and climate-related disasters have increased, but with large spatial and interannual variability (high confidence, based on high agreement, medium evidence). Global weather- and climate-related disaster losses reported over the last few decades reflect mainly monetized direct damages to assets, and are unequally distributed. Estimates of annual losses have ranged since 1980 from a few US$ billion to above 200 billion (in 2010 dollars), with the highest value for 2005 (the year of Hurricane Katrina). In the period 2000 to 2008, Asia experienced the highest number of weather- and climate-related disasters. The Americas suffered the most economic loss, accounting for the highest proportion (54.6%) of total loss, followed by Asia (27.5%) and Europe (15.9%). Africa accounted for only 0.6% of global economic losses. Loss estimates are lower bound estimates because many impacts, such as loss of human lives, cultural heritage, and ecosystem services, are difficult to value and monetize, and thus they are poorly reflected in estimates of losses. [4.5.1, 4.5.3.3, 4.5.4.1]

We are pleased to offer the reader a volume consisting of contributions of the Third George Kovacs Colloquium held in UNESCO, Paris from September 19 to 21, 1996. It is a continuation of a series of biannual international scientific meetings organized jointly under the auspices of the International Hydrological Programme (IHP) of UNESCO and the International Association of Hydrological Sciences (IAHS) in the challenging fields of water resources research. These meetings commemorate the late Professor George Kovacs, established authority in hydrology, who paid valuable service to both organizations convening this Colloquium. Professor Kovacs was Chairman of the Intergovernmental Council of the IHP of UNESCO and President of the IAHS.

The theme of the Colloquium, “Risk, Reliability, Uncertainty, and Robustness of Water Resources Systems,” denotesan essential recent growth area of research into water resources, with challenges and difficulties galore. The two-and-a-half-day Colloquium included twenty-four oral presentations covering a broad range of scientific issues. It dealt with different facets of uncertainty in hydrology and water resources and with several aspects of risk, reliability, and robustness.

The contributions to the Colloquium concentrated on the state-of-the-art approaches to the inherent problems. They also outline the possible future, identify challenging prospects for further research and applications. Presentations included both theoretical and applied studies, while several papers dealt with regional problems. Methodological contributions focused on underlying concepts and theories.

The presentations at the Colloquium, based on invitation, were delivered in three categories: keynote lectures, invited lectures, and young scientists' communications. Contributions belonging to all three categories are included in this volume.