Extreme Wind-Wave Characteristics in the North Indian Ocean in a Changing Climate

Wind-generated surface gravity waves are the manifestations of sea surface oscillations caused by intense wind stress and momentum transfer acting over the air-sea interface. Understanding the characteristics of wind-wave climate and its spatio-temporal variability over basin scales has significant practical applica-tions in almost all marine-related activities, ocean engineering, coastal zone manage-ment, naval applications, etc. In the recent past, the subject of extreme wind-wave activity in a changing climate and its impact on the Indian coast is a topic of immense interest amongst the scientific community having wider socio-economic consequences. Water levels in the nearshore regions due to extreme wind-waves have significant impacts on coastal environment, infrastructure, and dwelling popu-lation in the coastal regions. In a broader perspective, extreme waves are a part of the climate system and can be significantly influenced by the natural climate vari-ability. This chapter provides an overview on the generation and dissipation charac-teristics of wind-waves and the relevance of wind-wave climatology for the North Indian Ocean region. Recent trends observed in the extreme wind-wave activity in a changing climate scenario are a topic of wide interest. Extreme wind-waves and their return periods in a limited-fetch environment for the Arabian Gulf region are also discussed. Observed trends in extreme wind-wave activity for the extra-tropical regions in Indian Ocean and the North Indian Ocean showed an increasing trend at a rate of 3.3 cm/year and 0.27 cm/year, respectively. Also, in the recent decade an increasing trend is observed in the annual distribution of extreme winds and waves over extra-tropical regions having implications on generation of swell wave field that has consequence on local wind-waves in the North Indian Ocean region. Further, the case studies of extreme waves induced by tropical cyclones along with the recent trends in wind speed and its analysis based on global climate models are also discussed. Finally, a brief overview on the challenges and future directions for more research is also highlighted.