Past and Future Changes in Extreme Sea Levels and Waves

Abstract

Coastal impacts of sea -level change can result from individual extreme sea -level and wave events, or long -term fl uctuations in mean sea level, or most likely from a combination of processes. An example of a combined impact is the damage caused by Hurricane Katrina at New Orleans, which resulted in unprecedented storm -surge levels and failure of coastal defenses. This was compounded by the rate of local mean sea -level rise relative to the land level of the Mississippi Delta of several times the global average, as occurs naturally in all major deltas, together with anthropogenic changes to the delta wetlands. On much longer timescales, extremes and mean -sea -level change are both major factors in determining coastal evolution including the development of coastal ecosystems.It will be seen below that, although it is diffi cult to determine how mean sea level has changed in the past and will change in the future and to determine the reasons for change (the main topics of this volume), the very nature of extreme events makes estimation of future extreme levels a more diffi cult task. However, for many practical purposes, the study of extremes is far more important than that of mean sea level alone. Extremes often result in loss of life and great damage to infrastructure and the environment, and knowledge of their historical, and potential future, amplitudes and frequencies determines the scale of resources required for adaptation and coastal protection (see Figure 11.1 ).This chapter discusses changes in extreme sea levels and waves and is divided into four parts. First, we review changes in extreme sea levels and waves in the recent past. Then we discuss changes in the atmospheric storm events that drive extreme sea -level changes. There follows a review of recent advances in the modeling of future extreme events. (The reader is referred to the list of abbreviations and acronyms at the front of the book for models mentioned in the text.) The European shelf, Bay of Bengal and Australian regions have been investigated in greater detail than most other areas, and are selected for this section as special case studies of future change. Finally, we highlight issues that we believe need to be addressed in order to further understand the changes of the past and better predict those of the future.

Recent Change—Sea Level and Wind Waves

“…At many coasts around the world, extreme sea levels are essentially determined by tides; however, this effect is negligible in the Baltic Sea due to the semi-enclosed nature of the basin. Lowe et al (2010) Richter et al 2011) extreme sea levels in recent decades and concluded thatglobally-there is little evidence of change in extreme sea levels over an extended period, a behaviour which differs significantly from the change in GMSL. In their quasi-global investigation, Menendez and Woodworth (2010) showed that recent change in extreme sea levels is mostly due to the change in MSL (by a shift in the frequency distribution), while meteorological contributions vary on timescales of years and decades but mostly show no clear long-term trend.…”

Managing coastal environments under climate change: Pathways to adaptation

“…Future climate projections for European coasts, based on model ensembles, show SLR rates similar to global values (Lowe et al, 2010;Church et al, 2013). For low greenhouse gas (GHG) emission scenarios (SRES B2-A1B; RCP 2.6) mean SLR is likely to be in the range of 0.26-0.54 m above 1990 levels by 2080-2100.…”

“…Similar evolution trends apply to storm surges although in all cases due attention should be paid to the different behavior of mean trend and variance characterizing storms (Lowe et al, 2010). For instance, (Conte and Lionello, 2013) presented variations up to ±5% for both positive and negative surges in the Mediterranean Sea.…”

Climate variability and change: a perspective from the oceania region

“…Lowe et al [42] note that the rate and unpredictable nature of tsunamis means that they are probably under-estimated in probabilistic estimates of future extreme sea-level. In practice atmospheric drivers of extreme sea level such as mid-latitude and tropical storms are more amenable to analysis and prediction.…”