Abstract

Coastal flooding represent one of the major challenges of climate change for humanity, due to mean sea level rise over the coming centuries as well as the potential for changes in storm surge and wave climate. It is estimated that in 2005 in the largest 130 coastal cities there were 40 million people and $3000 billion of assets exposed to the 1 in 100 year flood event. These figures are predicted to rise to 150 million people and $35000 billion of assets by the year 2070. The most high impact examples of coastal flooding occur due to large storm events, often coinciding with extremely high tides. Any change in the statistics of flood frequency or severity will impact severely on economic and social systems. It is therefore crucial to understand the physical drivers of extreme storm surges, and to have confidence in datasets used for extreme sea level statistics.

This demands a consistent methodology to obtain a global climatology of storm surges combined with advanced statistical methods for estimating extreme sea levels. This presentation will outline a global project directed by the IOC -WMO Joint Commission for Oceanography and Marine Meteorology (JCOMM) expert team on waves and coastal hazards. I will present analysis of tide gauge data from the UK, Netherlands, Germany and Atlantic seaboard of the USA to provide baseline statistics for Atlantic storm surges. These methods can be extended to other regions including those affected by tropical cyclones. Much previous research has focussed on the process of tide-surge interaction, and it is now widely accepted that the physical basis of tide-surge interaction is that a phase shift of the tidal signal represents the effect of the surge on the tide. This presentation will show conclusively and for the first time that in extra-tropical regions the storm surge (when measured correctly) is independent from the tide. This implies that any storm surge can occur with any tide, although the probability may be very small.

Finally I will present plans to use a global tide-surge numerical model to provide a coherent global picture of storm surge climate. This could provide the basis of globally consistent vulnerability assessments that help disaster and risk reduction (DRR) agencies, and will also help planners and policy makers devise ways to mitigate coastal flood risk in the face of rising sea levels.