Changes in Extreme Sea-Level in the North Indian Ocean

Abstract

AbstractA review of studies on past changes and future projections in extreme sea level in the tropical oceans with a focus on the north Indian Ocean is made. Studies based on historical tide-gauge data for different oceanic basins show that changes in extremes are caused primarily due to changes in mean sea level. Analysis of data from tide gauges along the east coast of India and the head of the Bay of Bengal indicates similar results consistent with the studies elsewhere. Trends in extreme sea level are large (~5.0 mm/year) at Hiron Point, in the Ganga–Brahmaputra delta, pointing out that subsidence of the delta contributes considerably to changes in extremes through changes in mean sea level. Accurate assessments of the past changes and future projections of extreme sea level need data on rates of land motion. Besides, excess groundwater extraction in some regions is found to affect mean sea-level changes and its impacts on extremes are not fully understood. Extreme sea level along the east coast of India and the head of the Bay is found to have variability at different time scales such as seasonal and inter annual, with the latter having a correlation with modes of climate variability, such as the Indian Ocean Dipole mode and El Niño–Southern Oscillation. Region-specific modelling studies on projections of extreme sea level indicate that the increase in extreme sea level is associated with an increase in mean sea level, while a few studies show an increase with changes in storminess. The north Indian Ocean is one of the regions having the greatest threats from extreme sea levels, at the same time it is also a region that lacks sufficient observations, both in space and time, to facilitate climate studies related to extreme sea levels. The changing climate and increasing coastal population necessitate a systematic monitoring of extreme sea level through a dense network of observations along with Global Navigation Satellite System stations to monitor the land motions.KeywordsExtreme sea levelStorm surgeTideMean sea-level riseCoastal inundationNorth Indian Ocean