An indicator based approach for assessing the vulnerability of riparian ecosystem under the influence of urbanization in the Indian Himalayan city, Dehradun

Riparian ecosystems are critical biological habitat that needs to be preserved. These systems face multiple stresses of altered water regime, increased human interference and biological invasion, climate change, land developments and other site-specific issues that may include eutrophication and urbanisation. In due course of urbanisation, riparian vegetation is replaced by both impervious and less permeable surfaces causing more frequent floods, greater total surface runoff, and decreased time to produce runoff. This may result in flooding of the city when a substantial rain is received. In this study, we evaluated the vulnerability of riparian zones in Dehradun city of India due to urbanisation using a series of indicators extracted from remote sensing data. The changes in the landscape pattern of the riparian zones were examined by analyzing and manipulating Landsat-8 and Sentinel-2 datasets using Google Earth Engine, ArcGIS 10.1 and ERDAS IMAGINE 2014 software. Factors influencing the changes within the riparian area were identified using higher resolution image, existing base maps and reconnaissance surveys to qualify them as one of the indicators. Anthropogenic activities such as new residential buildings, infrastructure (such as roads), farming activities and commercial activities (industrial set up) were some of the factors contributing to the vulnerability of riparian zones. The final indicators in the form of riparian zone slope, extent of the riparian area, vegetation cover, human disturbance were mapped as raster layers and were integrated in a GIS environment to obtain final vulnerability map. This was intersected with settlement density map to categorize the vulnerability levels for three settlement density classes of low, medium and high. The findings reveal a significant land cover change within the riparian zones over a period of twenty years (2000 to 2019) with various levels of human encroachment. It was observed that 26.15% of the riparian area falls under low, 47.68% under medium, 12.98% under high, and 13.19% under very high vulnerability classes. Furthermore, the coverage percentage of high vulnerability class was largest in the low and high settlement density areas of riparian zones accounting for 36.96% and 51.48%, respectively. The majority of the area (74.36%) falls under medium vulnerability class under medium settlement density class. The study provides an opportunity to map riparian zone vulnerability considering predominant indicators of vulnerability that could be mapped using remotely sensed data and application of GIS tools.