The global sea surface temperature (SST) has increased throughout the past half-century due to the global greenhouse gas emission, leading to the intensification of cyclones over time . Globally, 40% of the world population resides within 60 km from the coast, a driver for the coastal vulnerability . The Intergovernmental Panel on Climate Change (IPCC) has identified several hotspots of climate change sensitive region where livelihood depends on subsistence agriculture, fishing, aquaculture . Vulnerable places experience damage of property, lives, and displacements. Aside from the direct losses, insecurity of food, lacking opportunity of employment, and health impairments are exacerbated by coastal hazards. Additional socio-economic impact is mainly accrued by developing nations due to low challenges to adaptation and high mitigations strategies . Over the decades, South Asia has experienced recurrent hazards related to tropical cyclones. The area is identified as a hotspot characterized by high population density, poverty, low development level, and exclusion . In the north Indian Ocean region, Bay of Bengal (BoB) alone accounts for 7% of all global cyclones of the world . Historically, coastal zones of India have attracted people due to port facilities, prosperity in agriculture, tourism, industries, trades, transport benefits, and habitable ecology [7, 8]. However, these regions are vulnerable zones due to the coincidence of low elevation, storm surges, floods, saline intrusion, coastal erosion , and other environmental challenges leading to infectious diseases and mortality [10, 11].
The coastal population of Indian subcontinent experience variety of coastal hazards of which cyclone is the most destructive one. With nearly 137 million populations  residing along with the BoB coastal districts and higher frequencies of depression-cyclonic storms, the coast is quite vulnerable as compared to the Arabian Sea coast in India due to higher frequency of cyclone (4:1 ratio of cyclones in Bay of Bengal than the Arabian Sea cyclone), low flat coastal terrain, high population density, poor knowledge of community, inadequate response and preparedness and absence of any hedging mechanism . Most recently, on 20th May 2020, the super cyclone Amphan lashed with 155 km/h, as tall as a two-story building on the Eastern coast and state of West Bengal in India . The devastation was amplified with strong winds, tidal waves, and heavy rains that caused flooding across the deltaic regions, with an estimated economic loss of US$13.5 billion . In the following year 2021, another cyclonic storm, named Yaas, intensified in the Bay of Bengal in May, and it has ravaged many parts of the apex of the BoB coast. India has witnessed severe to very severe cyclones: Laila, Helen, Phailin, Hudhud, Vardah, Ockhi, Titli, Gaja, Amphan and Yaas from 2010–2021  As a result of cyclone hazard proneness, the Indian Coastal Zone (CRZ) has demarcated 500 m from the shoreline as coastal vulnerability zones. However, a buffer of 100 km perpendicular from the shoreline is measured for coastal vulnerability assessments considering the coastal geomorphology . Literature suggests that, to escape from subsistence livelihood and poverty, aquaculture and industrialization have been introduced in these coastal regions, which had been the prime loop to coastal vulnerability .
Natural hazard vulnerability has a detrimental impact on human health, especially at conception and ending at the start of the third postnatal year (first 1000 days of life) [19–23]. Progressively, with the availability of satellite images and radar data, coastal hazard vulnerability assessments have soared [9, 17, 24–27]. However, a handful of scientists has conducted vulnerability assessment as a function of geomorphological, socio-economic, infrastructures, and other vectors [28, 29] The use of convoluted indices to understand the vulnerability has been adopted by many scholars like Cutter et al., 2006, who measured Social Vulnerability Index (SVI) using socio-economic and infrastructural indicators. Kim and Gim (2020) measured flood vulnerability and adaption along the Java coast, integrating the spatial regression model . In India, Mazumdar and Paul (2016) and Sharma and Patwardhan (2008) measured the SVI due to cyclone with the principal component method. Scientists have studied the extreme effect of climate variability on health and mortality trajectories [34, 35]. Maternal exposure to cyclone increases the risk of having preterm [36–38] birth and consequently plays critical role in neonatal mortality [39, 40]. Past study observed that tropical strom increases the risk of illness, injuries and health needs .The risk of disease transmission tends to heighten in developing countries due to population density, inadequate sanitation, and poor health facilities. The outbreak of gastroenteritis and diarrhoeal disease has been documented in the parts of West Bengal, India, after Cyclone Aila, 2008 [42, 43]. Other morbidities like acute respiratory diseases, leptospirosis have been reported following a cyclone in Orissa, India, in 1991 . The extreme weather events have a significant impact on the health of a child [45, 46]. Female infant mortality was 15.1 times higher than males in a natural disaster as observed in Philippines . Furthermore, a cross-country analysis of 12 developing countries indicated an increase in infant mortality due to the cyclone's long-term effect . As cyclones have the potential to cause infant and under 5 mortality, empirical studies suggest that natural hazard-induced child mortality positively responds to higher fertility rates [49, 50].
The rich body of literature in this field mainly focused on different natural hazard vulnerability assessments or aftermath of extreme events. Studies in India are rare in this field, especially highlighting aggregate measurement of vulnerability based on public data and revealing the associations of vulnerability and child health. The present study, unique in its approach, aims to estimate vulnerability at coastal districts of the Bay of Bengal, consisting of 45 districts within a 100 km buffer zone along the coastline. We made progress on integrating the vulnerability and its effects on health by considering two crucial health indicators, i.e. neonatal and under-5 mortality. The study adds to the literature by providing additional evidence of socio-economic vulnerability as a function of exposure, adaptation, and sensitivity due to cyclones and its linkages to child mortality in India.