Baltic Earth Working Group on Natural hazards and extreme events in the Baltic Sea region

Background and objective

A natural hazard is a naturally occurring extreme event with a negative effect on people or the environment. Natural hazards may have severe implications for human life as they potentially generate economic losses and damage ecosystems. A better understanding of their major causes and implications enables society to be better prepared and to save human lives and mitigate economic losses. Many natural hazards are of hydro-meteorological origins (storms, waves, flooding, droughts) and are often caused by a mixture of several factors (e.g. a storm surge in combination with precipitation and river runoff, which might generate extreme flooding). Average changes in the recent climate in the Baltic Sea region are relatively well described, but the uncertainty is much larger for extreme conditions. These extreme events pose a substantial threat to infrastructures or ecosystems albeit their relative rareness. The shortage of available data on these events reduces the statistical significance in the analysis and the capability to predict them.

This is generally well recognized regarding infrastructure such as dam safety and urban flooding risks, but the range of ecosystem services at risk is more poorly defined, from vital societal functions such as drinking water supply to biodiversity. The resilience and adaptation capability of terrestrial and marine ecosystems and organisms as well as human society to environmental changes depends very much on the future severity and frequency of extreme events.

There are meteorological implications of global warming, which may be the cause for changed frequencies of these extreme events. Storm tracks on the Northern Hemisphere seem to have shifted slightly northward during the last century as a consequence of global warming, and there are indications of additional Northern Hemisphere circulation changes due to the significant reduction of Arctic ice cover. Their connections, however, are not clearly understood and described, and there is a need to further investigate this with a Baltic Sea perspective. Hence, key processes and factors (e.g. atmospheric circulation, Arctic sea ice, snow) responsible for the changes in extreme events in the study region as well as their interlinkages, need to be better understood. An improved understanding of air-sea-land processes and the development of more detailed models is crucial.

Description of tasks (or Terms of Reference)

Potential activities include the improvement of monthly to seasonal prediction systems and probabilistic estimates of the extreme events, a specific attribution analysis of past extreme events to elucidate the possible role of anthropogenic forcing factors, and an analysis of the vulnerability of key societal functions to changed hydro-meteorological extremes. Furthermore, it should be investigated if and how environmental goals are compromised by changing extremes such as droughts, floods or heat waves, including responses of the carbon cycle and the Baltic Sea carbon budget. Review papers and workshops will provide a discussion platform to help achieve the goals.

Members of the Working Group on Natural hazards and extreme events in the Baltic Sea region

Anna Rutgersson (Chair) University of
Jari Haapala (vice)FMI,
Martin Stendel (vice)