Natural Hazards and Extreme Events in the Baltic Sea region 1

Department of Earth Sciences, Uppsala University, Uppsala, Sweden 6 Centre of Natural Hazards and Disaster Science, Uppsala University, Uppsala, Sweden 7 Swedish Meteorological and Hydrological Institute, Norrköping, Sweden 8 Department of Meteorology and the Bolin Centre, Stockholm University, Stockholm, Sweden 9 Finnish Meteorological Institute, Helsinki, Finland 10 Danish Meteorological Institute, Copenhagen, Denmark 11 Institute for Nature Management, National Academy of Sciences, Minsk, Belarus 12 Department of Technology, Management and Economics, Technical University of Denmark, Kgs. Lyngby, 13 Denmark 14 Aalto University, Espoo, Finland 15 Wind Energy Department, Technical University of Denmark, Roskilde, Denmark 16 Leibniz Institute for Baltic Sea Research, Warnemünde, Germany 17 18 Correspondence to: Anna Rutgersson (anna.rutgersson@met.uu.se) 19 20 Abstract. 21 A natural hazard is a naturally occurring extreme event with a negative effect on people and society or 22 the environment. Natural hazards may have severe implications for human life and they can potentially 23 generate economic losses and damage ecosystems. A better understanding of their major causes, 24 probability of occurrence, and consequences enables society to be better prepared and to save human 25 lives and to invest in adaptation options. Natural Hazards related to climate change are identified as one 26 of the Grand Challenges in the Baltic Sea region. We here summarise existing knowledge of extreme 27 events in the Baltic Sea region with the focus on past 200 years, as well as future climate scenarios. The 28 events considered here are the major hydro-meteorological events in the region and include wind storms, 29 extreme waves, high and low sea level, ice ridging, heavy precipitation, sea-effect snowfall, river floods, 30 heat waves, ice seasons, and drought. We also address some ecological extremes and implications of 31 extreme events for society (phytoplankton blooms, forest fires, coastal flooding, offshore 32 infrastructures, and shipping). Significant knowledge gaps are identified, including the response of large 33 scale atmospheric circulation to climate change, but also concerning specific events, for example, 34 occurrences of marine heat waves and small-scale variability of precipitation. Suggestions for future 35 research includes further development of high-resolution Earth System models, and the potential use of 36 methodologies for data analysis (statistical methods and machine learning). With respect to expected 37 impact of climate change, changes are expected for sea-level, extreme precipitation, heat waves and 38 phytoplankton blooms (increase) and cold spells and severe ice winters (decrease). For some extremes 39 (drying, river flooding and extreme waves) the change depends on the area and time period studies. 40