Table 1.

Physical variables significance and source with respect to coastal vulnerability

S No.	Variable	Derived by	Significance	Source	Year	Ground Truth
1	Coastal slope (degree) (Figure 3)	Referred to CVI of Goa coast by Kunte et al.	Locations with gentle slope are more prone to flooding as gentle slopes retreat faster than steeper slope and wave energy can penetrate far inland due to less frictional force restricting it.	ETOPO2 bathymetric dataset from the NIO, Goa	1971–1984	The devastating Indian Ocean tsunami in 2004 profoundly impacted the coastal city of Banda Aceh, Indonesia. The coastal areas with gentle slopes were more vulnerable to the powerful tsunami waves that penetrated far inland, causing widespread destruction. The lack of natural barriers and the flat terrain allowed the waves to travel farther inland, causing more extensive flooding.
2	Coastal regional elevation (m)	SRTM 30m DEM, using QGIS	Coastal regional elevation is an important parameter as it provides an estimate of the extent of land threatened by projected SLR (Kumar and Kunte, 2012; Kumar et al., 201014), and the coast's sensitivity to flooding during a storm surge15 or tsunami. Hence, areas with high coastal elevation will be considered less vulnerable and vice-versa.16	SRTM 30 m DEM	2019	The 2011 Tōhoku earthquake and subsequent tsunami in Japan highlighted the importance of coastal elevation in tsunami vulnerability. For example, the city of Aonae in the Miyagi Prefecture suffered less severe impacts due to its elevated location on a hillside.
3	Sandy coast (%)	Total sandy coast length in each village/Total coastline length of each village x 100.	Sandy coasts have gentle slope toward inland which makes their inland areas more vulnerable to coastal flooding. Higher the amount of sandy coast in a given transect higher will be the vulnerability.	Google Earth and Digimizer	2019	Hurricane Sandy, had a profound impact on the northeastern United States. New Jersey was severely affected. It has a significant stretch of sandy coastline with relatively gentle slopes. During Hurricane Sandy, the storm surge inundated large portions of the coast, flooding coastal communities and causing extensive damage. The combination of the storm surge, high tide, and the gentle slope of the sandy coast contributed to the widespread flooding.
4	Dune density	Dune areas from the NCSCM study were digitized and measured using Digimizer software	Sand dunes protect the inland area from seawater intrusion during high tides and act as a reservoir for future supplies to maintain the beach. Sparse sand dune areas are more vulnerable as there is no restriction between the sandy beach and inland areas.	NCSCM 2017, Field Study	Oct, 2019	The Dutch coast along the North Sea features an extensive sand dunes system critical in protecting the low-lying coastal areas from flooding and erosion.
5	Vegetation behind the beach	Vegetation areas in the imageries were measured using Digimizer software.	Casaurina and coconut plantation help decrease the energy from cyclonic winds and storm waves, reducing the risk of inland damage. Dense vegetation could lessen the vulnerability	Field survey, Google Earth Imageries and Digimizer	Sept 2019	Chennai, India, has been vulnerable to the impacts of cyclones and storm surges. In response, the Tamil Nadu Forest Department established casuarina plantations along vulnerable stretches of the coastline. These casuarina plantations act as windbreaks and help protect coastal communities from the destructive forces of cyclonic winds and storm waves.
6	Rate of relative SLR (m)	Adopted from the CVI of Goa coast by Kunte et al.	A higher SLR increment rate will increase the vulnerability as it denotes increasing the risk of inundation in low-lying coastal areas.	Annual mean relative sea level data from Indian Ocean tide gauge stations 1969–2017.	1969–2017	Bangladesh is a densely populated country with a significant portion of its population residing in low-lying coastal areas. The combination of higher sea-level rise rates and flat topography makes these areas particularly vulnerable to coastal inundation, which can lead to community displacement and loss of agricultural land.
7	Shoreline erosion rate (m)	Adopted from Indian Shoreline Atlas, 2018	Shoreline erosion rate over some time indicates the sensitivity of the coast, thus increased vulnerability.	NCCR, MoES 2018	2018	The Chesapeake Bay region has experienced significant shoreline erosion due to various factors, including sea-level rise, wave action, and human activities. Erosion along the bay’s coastlines has led to the loss of valuable land, including residential properties and infrastructure.
8	Mean tidal range (m)	Data from the National Institute of Oceanography, Goa	Coastal areas with high tidal range and low coastal regional elevation are highly vulnerable.	NIO, Goa India, 2011	2011	Coastal regions along the Bay of Bengal in India, such as parts of West Bengal and Odisha, experience high tidal ranges due to the bay’s unique geography. Low-lying coastal areas in these regions are particularly susceptible to cyclones and storm surges, leading to flooding, erosion, and damage to homes and infrastructure.
9	Significant wave height (m)	Data from the National Institute of Oceanography, Goa	The average height (trough to crest) of one-third of the waves in a wave spectrum for a given period.14 Dwarakish et al. (2009) considered significant wave heights range from 1.6 to 2.8 m as moderately vulnerable.	NIO, Goa, India using studies on directional waves off Mormugao Port, 2009	2009	Coastal regions along the Bay of Bengal, such as parts of Bangladesh, India, and Myanmar, are exposed to high significant wave heights and storm surges during cyclones. These factors leads to extensive coastal flooding, erosion, and damage to homes and infrastructure.
10	Plausible storm surge height (m)	Derived from Vulnerability Atlas of India, 2019	Due to its high-intensity waves, storm surges can destroy low- lying coastal areas. Thus, surge height in any region is an important criterion.	BMTPC, Ministry of Home and Urban Affairs	2019	The surge height associated with Hurricane Katrina reached approximately 28 feet (8.5 m) in some areas along the Gulf Coast. The storm surge inundated large portions of low-lying coastal regions in Louisiana, Mississippi, and Alabama, causing catastrophic flooding, destruction of infrastructure, and loss of life. The surge height played a central role in the unprecedented devastation experienced by the affected communities.