Integrated vulnerability assessment of Karnataka Coast, India: A Geospatial approach

Abstract

Coastal environments are important ecological hotspot for all living organisms. Coastal environments support a large species of indigenous fauna and vegetation with a high biological diversity. Even the human population density in coastal areas is estimated to be three times the global mean. In recent times, increased and the rapid development at the coastal regions has strained the coastal ecosystems in the form of destruction and degradation. Change in globe’s atmospheric conditions has also increased the frequency of coastal hazards such as floods, hurricanes and storm surges. The sea level rise due to the global warming, along with the frequent storms, forms a looming threat to our coastlines. Mitigation of a potential disaster requires a detailed knowledge about vulnerability of the places to various hazards. Such vulnerabilities may be associated with natural or social hazards, or sometimes a combination of both. A systematic vulnerability may be carried out only if the various dimensions involving a hazard are considered. Vulnerability studies generally undertaken skip a very important aspect of human interaction with the nature. Researchers have insisted on inclusion of human interaction as a socio-economic variable in assessment studies. Most of the studies have been carried out using physical variables; Shoreline change rate, Sea-level change rate, Coastal slope, Significant wave height, Tidal range, Coastal regional elevation, Coastal geomorphology and very few studies have been carried out by combining socioeconomic variables along with the physical variables. Also very few studies have evaluated the effect of Tsunami and storm surge as variables for determining CVI. Most often CVI is calculated using the USGS equation. However, researchers have highlighted that the equation has a disadvantage for usage as equal weights has been assigned to all the variables even when the influence of one variable is more than that of the other variable. On the other hand, assigning random weights to variables can also be logically a mistake as weights are influenced by discretion of the individual researcher. In addition, it was found that the CVI calculated using USGS equation underestimates the risk of certain stretch of coast, which is highly prone to erosion. Hence, in the present study, an opinion survey of experts from ocean and coastalii engineering discipline was carried out and a weight scheme was formulated using the principles of Analytical Hierarchical Process (AHP). Tsunami vulnerability for regional scale using GIS was also carried out in the present study. Four geospatial variables, viz., topographic elevation, topographic slope, coastal proximity and vegetation were used to create a tsunami vulnerability map. It was found that Karnataka coast has 71.92 km length of coast in ‘very high vulnerability’ category, while 71.25 km was under ‘high vulnerability’ category. The extent of ‘moderate vulnerability’ and ‘low vulnerability’ was 71.20 km and 80.69 km, respectively. An overlay of the landuse classification on the tsunami vulnerability map showed that habitation (206.403 km2) and cropland (181.103 km2) are the two major classes of the study area, which are in high-risk category. It was also noticed that coast of Udupi and Magaluru talukas were most vulnerable coast of the study area. In addition, the use of AHP for assignment of weights to variables has provided the realistic scenario for the vulnerability assessment. The MCVI developed in the present study evaluated the level of risk on different segments of the coast. The maps developed in the present study are useful to identify areas where physical changes are most likely to occur in case of a coastal hazard, and as well in planning, managing and protecting resources in the study area.