Extreme wind-wave climate projections for the Indian Ocean under changing climate scenarios

Extreme wind-waves will impact coastal regions along the east and west coast of India and countries bordering the Indian Ocean rim having implications on coastal flooding and shoreline changes. Detailed investigation was carried out in this study on future extreme wave projections and its relationship with wind speed, sea level pressure (SLP), and sea-surface temperature (SST) for the mid- and end-century under RCP4.5 and RCP8.5 emission scenarios. Projections collectively highlight on maximum extreme wind and wave activity for south Indian Ocean (SIO) during June-July–August (JJA) and September–October–November (SON) seasons. Results indicate that end-century projections show extreme wind activity over central Bay of Bengal (BoB) signifying the likelihood for more extreme events over this region. Mid-century projections show that extreme significant wave height (SWH) intensifies by 1 m for the SIO during JJA season. Also, an increase of 0.4 m in maximum SWH (Hmax) is projected for regions in the NIO, northwest AS, northeast BoB, and South China Sea (SCS). Projections for eastern SIO show strengthening of extreme wind speed by 3.0 m/s by the end-century under RCP8.5. The projected changes in Hmax is maximum for SCS region evident in RCP4.5, whereas the maximum rise is about 23% under RCP8.5 in the end-century. Projected decline in winds and waves over western tropical IO (TIO) is consistent with weak SLP variations and warm ocean temperatures over that region. Significant increment in SST is projected over entire AS during DJF and JJA seasons ranging between 1.5 and 2.0 °C, which is 0.5 °C greater than BoB. Projections for the Gulf of Oman and Persian Gulf show higher warming rates exceeding 2 °C under RCP8.5 by the end-century. Warming in these areas further reduces SLP gradient leading to enhanced weakening of low-level atmospheric circulation and declining Hmax by the end-century. A westward alignment in these areas with maximum projected changes in SST is noticed in most seasons. Detailed analysis of high wave activity regions shows widening of generalized extreme value fitted probability density function over the BoB, SCS, and SIO indicating more extreme wave activity in the future.