Obtaining typhoon information from sedimentary records in coastal-shelf waters

The typhoon intensity-frequency relationship over a long period of time is related to climate change, but it is difficult to provide sufficient information from instrumental and historical records. Therefore, to extract storm information from sedimentary records has become a critical scientific problem; the solution to the problem can provide a decision-making basis for coastal cities to cope with future climate and sea level changes. The present study on the progress in the research of typhoon sedimentary records shows that shelf mud deposits, beaches and coastal dunes, tidal flats, lagoons and storm boulders contain records of extreme events. These event layers can be identified by stratigraphic sequence features and sediment characteristics. Typhoon records along the coastline of China have been found in large quantities, but further improvements to the information-obtaining methodology are needed to distinguish between deposits of typhoons, winter outbreaks, river floods and tsunami events. Thus, in terms of the information on typhoon intensity in shelf muds, coarse-grained and shell particles in the deposits can be used as indicators of intensity of bottom resuspension, but calibration with sufficient measurements is required. The elevation of typhoon deposit on the top of beaches and coastal dunes may indicate the height of swash during a typhoon event, while the size of storm boulders has a significant correlation with the offshore wave height. These data can be used to deduce typhoon intensity, although they are not enough to establish the intensity-frequency relationship. Tidal flat and lagoon deposits have a high continuity and can be used to reconstruct the time series of typhoon events. However, the solution to typhoon intensity is not unique because different combinations of maximum wind speed, path, landing place and duration may produce the same event deposit. We propose that a new method of obtaining typhoon information should be developed to solve this problem. Numerical simulation of modern process, with the help and assimilation of available data and knowledge of typhoon events, would be useful to reproduce the characteristics of event deposits. Then, inverse simulation for event deposits can be carried out for multiple locations, to constrain the solution domain. This method may be referred to as "solution domain constraining method". The uncertainty can be further reduced by means of big data analysis, i.e., incorporating other dataset of typhoon intensity into the simulation system. A combination of dynamic process simulation and big data treatment is helpful to the establishment of the intensity-frequency curve of typhoon with the same time scale as the sedimentary record; on such a basis, the relationship between typhoon variation and climate change can be analyzed.