Evolution of extreme high waters along the east coast of India and at the head of the Bay of Bengal

• Spatial pattern, inter-annual variability and long-term changes in extreme high waters in the Bay of Bengal are detailed.
• Extreme high waters are found to be a combination of high tides and low or moderate surges.
• Extreme high waters are found to be influenced by ENSO and IOD.

The recent evolution of extreme high waters along the severe cyclone-risk coasts of the Bay of Bengal (the east coast of India and Bangladesh) was assessed using long-term (24–34 years) hourly tide gauge data available from five stations. The highest water levels above mean sea level have the greatest magnitude towards the northern part of the Bay, which decreases towards its south-west. Extreme high waters were observed to result from a combination of moderate, or even small, surges with large tides at these stations in most of the cases. Increasing trends, which are significant, were observed in the extreme high waters at Hiron Point, at the head of the Bay. However, the trends in extremes are slightly lower than its mean sea level trend. For the other stations, Cox's Bazaar, Paradip Visakhapatnam and Chennai, no significant trends were observed. At inter-annual time scales, changes in extreme high waters in the Bay of Bengal were found to be influenced by the El Niño Southern Oscillation and the Indian Ocean Dipole.