Geospatial Assessment Of Urban Sprawl Using Remote Sensing And GIS: A Case Study of Western Himalayan City of Dharmashala, Himachal Pradesh, India.

The small cities in the Asian subcontinent are supposedly going to witness exponential growth in the next two decades. The situation could be very challenging in Himalayan cities owing to topo-geographical complexities and limited resources in the region. The increasing population coupled with being a favored tourist destination had resulted in dispersed, inefficient, and unplanned built-up activities in the region. Monitoring the urban sprawl can help in adopting sustainable development strategies equally balanced towards the society and environment. The availability of geospatial data integrated into the GIS interface can help immensely in monitoring and measuring LULC changes and thereby help in formulating necessary interventions and strategies for realizing a sustainable ecosystem. The present study employs Landsat imagery for creating the built-up land cover maps for the year 2016, 2019, and 2022 and the ALOS-PALSAR Digital Elevation Model for understanding the trend and direction of urban sprawl in Dharamshala city. It was found in the study that the built-up dynamic index had increased to 23.3% from the year 2016 to 2022. The built-up growth rate for the study period was found to be 145% for the elevation less than and equal to 1000m, 143% for elevations ranging from 1000-1500m, and 119% for the elevation greater than 1500m. The built-up growth rate for a distance up to 100 m from the streams was 119% from the year 2016 to 2022. The geospatial risk assessment highlights potential threats in the region due to increased built up activities, emphasizing the need for prompt intervention by policy-makers, administrators, and environmentalists to advocate for a sustainable development model.


INTRODUCTION
The rapid expansion of urban sprawl, driven by socio-economic development, has emerged as a highly dynamic land cover phenomenon on a global scale but has significantly impacted the pursuit of a sustainable development model [1].Urban sprawl is supposed to have three dimensions: built-up area (amount), its dispersion in the landscape (spatial configuration), and the utilization of area per inhabitant or job [2].The amount and spatial configuration of built-up had been severely impacted by the increasing population, which has been considered by most researchers to be one of the major driving factors for urban sprawl [3,4].With the projected global population to be around 9.7 billion by 2050 (United Nations, 2022), the challenge to curtail urban sprawl is poised to reach its peak [6].The implications of urban sprawl on demography and the associated environment is palpable and accompanies deforestation, industrialization, and traffic congestion [7].
The geo-spatial assessment of a region through the use of remote sensing and GIS has been receiving significant attention from researchers, policy-makers, administrators, and environmentalists in the Himalayan region [8][9][10].The attention is primarily driven by the observable impact on the bio-physical and socio-economic aspects [11,12].The altered land use has given rise to critical issues regarding the socio-ecological system (SES), biodiversity, biological carbon sequestration, encroachments, land degradation, floods, landslides, carbon storage, and medicinal plants, among others.The functioning and structure of the ecosystem have been radically altered aided by the pressing demands and satisfaction levels induced by anthropic activities ultimately leading to the vulnerability of places, people, economic dynamics, and climate [7].The remote sensing data when embedded in a GIS interface facilitates a comprehensive approach for measuring and monitoring the intricate changes occurring in a particular region [13][14][15].This approach can provide meaningful revelations for the formulation of policies and laws that balances and regulates the urban sprawl with sustainable development model practices.
The geographical, topographical, and seismic conditions in the Himalayan regions pose unique and complex challenges and vulnerabilities [16].Vulnerability refers to the degree a system is susceptible to hazard and essentially encompasses two significant aspects: 1) exposure to a threat and 2) the resultant losses, which may be in the form of monetary impacts or casualties when subjected to the identified threat [17,18].The geospatial assessment of the region can provide valuable insights into the vulnerability aspects and help in proposing remedial and intervention strategies.
The increased built-up activities lead to increased peak flow conditions with an attenuated peak discharge time [19] and thus making the regions more vulnerable lacking proper drainage and urban planning [20][21][22].The threat to the built-up establishments near the streams increases manifold due to the peak discharge caused as a consequence of this.The proliferation of built-up areas near streams in Himalayan regions is a major cause of concern and the vulnerability in respect of flash floods caused urban flooding and landslides increases manifold.
Various studies [13,[23][24][25][26][27] carried out in the Himalayan region have shown a sharp decline in forests at the cost of increased built-up areas.The spatial-temporal analysis of declining forests using DEM has been widely accounted for in Himalayan regions.The studies by [28][29][30][31] have used slope and elevation to comprehend the trend and direction of LULC changes.
The population, tourism industry, and increased socio-economic aspiration have been the major driving factors of change in the Himalayan region [32][33][34].Further, the policy and law decisions to promote and boost the tourism, hospitality, agro-forestry, and recreational sectors, had led to unprecedented wanton appropriation for built-up areas in the region which is not in line with the sustainable ecosystem and environment.
Remote sensing (RS) imagery and GIS offer a cost-effective and efficient system to prepare a sustainable roadmap for the development of any region [35][36][37].The geospatial assessment of the region involving spatio-temporal analysis through the use of the Digital Elevation Model (DEM) can help in understanding the trend and direction of urban spraw [12,38,39] .Further, the spatial proximity analysis of the built-up areas near the streams can provide valuable inputs related to the dangerous building practices in the region.
To summarise urban sprawl can have serious implications in a region with the need to formulate and regulate the policies that are in line with sustainable development.The research study has three main objectives: 1) To measure the trend and direction of spatio-temporal builtup activities in the region using RS, GIS, and DEM. 2) To perform spatial proximity analysis of built-up areas within 100m of the streams in the study area.3) Assessment of driving factors responsible for the change.

STUDY AREA
The study area, Dharamshala, shown in Figure 1 is situated in the Western Himalayas on the southern slopes of the Dhauladhars, a major mountain range in Himachal Pradesh, India, covering an area of 42.7 km 2 .The study area lies between latitudes 32°9'52" N to 32°15'58" N and longitudes 76°17'22" E to 76°23'09" E. The elevation varies significantly, ranging from 790 m in the southwest region to 2130 m above mean sea level (AMSL) in the northern parts of the area.During winter, the northern part of the region experiences snowfall of moderate to heavy intensity.
The city experiences a moderate mean annual temperature of approximately 19.1 ± 0.5°C.The warmest month is June, having a maximum average temperature of 32°C, while the coldest month is January, having a minimum average temperature of 10°C.Additionally, the annual average rainfall in the area is 2900 mm approximately, contributing to its relatively wet climate [4].The northern parts of the region also receive heavy snowfall during the winter season.
Land use records from 2016 reveal that more than half of the area is covered under forests.The dominant soil order, as per USDA soil taxonomy, is Alfisols, primarily due to the extensive forest cover in the region.Overall, the city of Dharamshala exhibits diverse topographical and climatic characteristics, with significant variations in elevation, temperature, and precipitation.Its substantial forest coverage and prevalence of Alfisols highlight the importance of understanding the ecological dynamics and implications for land management and environmental conservation in this region.

MATERIALS AND METHODS
Multi-temporal Landsat 8 Operational Land Imager (OLI) satellite imageries from the years 2016, 2019, and 2022 were utilized.The selected images were obtained for the month of May from the United States Geological Survey, Level 1 and cloud free (< 5% coverage), in GeoTIFF format and were projected to the World Geodetic System 1984 Geographic Coordinate System.This approach helped to mitigate the impacts of phenological effects and reduce cloudy pixels, thereby enhancing the accuracy of the results.
To complement the Landsat data and create a drainage network of the major streams in the area, an ALOS-PALSAR DEM was also employed.The DEM was used for calculating the parameters such as slope, elevation and distance from the streams.The details of the dataset used in the study is shown in Table 1.
In addition to the satellite and DEM data, ancillary data were integrated into the study.These included a Town and Country Planning (TCP) Report of Dharamshala city and Ground truth points, which were established using GPS technology.The population and tourist data from Economics and Statistics Department, Govt of HP, was used in the study.
By incorporating these various data sources and adopting a focused methodology, the study aims to provide comprehensive and reliable insights into the landscape changes and features of the study area over the selected years.The methodological workflow incorporated in the study is shown in Figure 2

Pre-processing
Pre-processing involves the methods to enhance the accuracy and reliability of the data acquired by sensors on satellites or other platforms [40].The geometric correction of the study area was performed by a suitable selection of GCP such that RMSE was reduced to less than half of the pixel [22].The satellite imageries of 2016, 2019, and 2022 were registered into the Universal Transverse Mercator Coordinate system (Zone 43N).The radiometric correction involved the conversion of Digital Numbers into radiance, transforming the radiance at the sensor to Top of Atmosphere (ToA) reflectance and converting ToA reflectance to surface reflectance using Dark Object subtraction (DOS) in Semi-Automatic Classification (SCP) plugin of QGIS [1,41].

Built-up areas classification
Maximum Likelihood Classifier (MLC) has been widely used in Himalayan regions for the classification of land cover classes [13,16,26,42,43].LULC built-up map for the years 2016, 2019, and 2022 was created using MLC which utilizes the class statistics derived from labeled training samples and assigns each pixel to the most probable class membership given the pixel's spectral values and the statistical information of the classes [44].Thus LULC map consisting of two classes, built-up and non built-up areas was created.
The built up dynamic index (k) measures the degree of change in built up areas for a certain period and is calculated using the formula in eq. ( 1)

Geo-spatial parameters
The DEM consists of a grid of elevation values, represented by regularly spaced pixels, where each pixel contains a numerical value representing the height above or below the reference point.Slope and elevation are two important static geophysical parameters, each having a very important role in urban sprawl [45,46].Elevation controls the micro-climate, soil, and vegetation type, while slope plays key a role in settlement distribution [47].The slope and elevation when overlayed over the satellite imageries can provide valuable insights regarding the urban sprawl.Lesser slopes and elevations offer more favorable conditions for development [48] and thus may witness high urban sprawl.Slope involves assessing the steepness or inclination of the terrain at each point on the Earth's surface The inclination of the terrain with respect to the horizontal plane is represented by the slope, which is then expressed as a percentage or in degrees.The slope is classified as gentle if less than and equal to 15%, moderate if varies from 15-25%, and steep if greater than 25% [43] Elevation is calculated by measuring the vertical distance between the Earth's surface and a reference point, usually the mean sea level.

Spatio-temporal Proximity near Streams
The proximity of built-up to natural streams may become a serious cause of concern in urban flooding scenarios [21,49].The situation may become critical in Himalayan cities in the event of extreme rainfall-induced flash-flood, landslides and cloud-burst.The built-up activities near the streams impact the geomorphological and hydrological characteristics making these regions more vulnerable than before [50].The anthropogenic activities and urbanization have been considered to be major reasons in Dharamshala for constricting the natural drainage of streams and thus causing more damage to life and property [51].Spatio-temporal proximity analysis around the streams can help in monitoring and identification of the areas having such threats.

Spatio-temporal Built up area Analysis
The increase in built-up areas during the study period is shown in Figure 3.The built-up dynamic index calculated using eq.1 is shown in Table 2, and was found to be 23.

Geo-spatial parameters analysis
The urban sprawl during the study period according to elevation and slope is shown in Figure 4 and Figure 5 respectively.The LULC built-up area distribution according to elevation and slope is shown in Table 3 and Table 5, respectively, signifying a higher concentration of built-up areas at altitudes less than 1500 m and on slopes less than 25%.
The urban sprawl based on elevation and slope criteria is shown in Table 4 and Table 6, respectively.Agricultural areas lying predominantly in lower elevations, less than 1500 m, and slopes less than 25% have been converted into built-up areas with a growth rate of around 140% in each, signifying the shift in occupation of the city-dweller and the study area rapidly turning into a concrete jungle.An increase in built-up areas at higher altitudes (more than 1500m) and steep slopes (>25%) is a serious cause of concern given the fact that most of these regions are covered under forests.The urban sprawl in these regions indicates illegal encroachments in the region.

Spatio-temporal proximity analysis near Streams
The built-up area distribution at a distance of 100m from the streams is shown in Figure 6 and the built-up growth rate calculated is shown in Table 7. Urban Sprawl near streams An increase of 23.3% from the year 2016 to 2022 was witnessed in the built-up areas near the streams, indicating a possibility of a major catastrophe in the future.Increased built-up activities near the streams have serious implications on the aquatic and ecological balance of the region, thus impacting the overall socio-ecological process.The urban sprawl near streams also requires attention from the risk arising due to landslides and loss of life and property on account of cloudburst conditions in the region.in all the Class -III cities (having populations from 20,000 to 50,000) of Himachal Pradesh.The ongoing and projected surge in road construction and recreational pursuits, coupled with the persistent expansion of urban areas into increasingly challenging and complex terrains, is anticipated to render the entire city susceptible to the potential hazards of landslides, earthquakes, and cloud-bursts, leading to significant risks of loss of life and property.Through the integration of remote sensing and Geographic Information System (GIS), it becomes feasible to conduct a comprehensive geo-spatial evaluation of an urban area, facilitating the formulation of an actionable strategy that effectively harmonizes developmental needs with environmental conservation objectives.
The escalating expansion of built-up areas, driven by population growth and tourism, and the identification of vulnerable areas through this research will help in taking into account factors such as infrastructure development, resource efficiency, and the integration of green spaces, to foster the creation of urban environment characterized by livability, thereby enhancing the overall quality of life for the resident population.The study advocates environment conservation strategies in the region involving afforestation programs, environment protection campaigns, and the identification of areas vulnerable to landslides, earthquakes, and cloudbursts.The conducted research found that the built-up dynamic index was 23.3% in six years from 2016 to 2022.The situation could have been worse had not there been Covid related restrictions.It revealed that areas situated above 1500 m altitude with slopes exceeding 25% necessitate meticulous monitoring due to their geographical-seismic attributes, which significantly elevate the vulnerability of built-up structures to heightened risks of loss of life and property.The increased built-up activities at high altitudes indicate possible encroachments in the region as mostly such areas are covered under Forest.Additionally, the escalating concentration of built-up areas close to streams is projected to severely impede both aquatic ecosystems and microclimatic conditions.Further, an action plan for regulating the built-up activities is required.The findings in this research underscore the urgency of formulating an action plan based on a sustainable development model that effectively harmonizes developmental requirements with environmental preservation imperatives.A Sustainable Model that includes various stakeholders in the decision-making process will foster a sense of ownership and encourage collaborative approaches.Engaging local communities and considering their perspectives can lead to more inclusive and equitable land-use planning, ensuring that the benefits and burdens of land-use changes are shared among all members of society.The activities such as afforestation and awareness programmes, enforcement of strict laws to check illegal encroachments, restoration and incentivizing agricultural practices as a measure to check built-up concentration and ensuring proper drainage in the area to check peak flow conditions as a consequence of increased built up areas and implementation of effective land use/ resource management strategies need to be implemented in the region.
4, 13.7, and 23.3 for the years from 2016-2019, 2019-2022 and 2016-2022 respectively.The study area a substantial transformation of non-built-up regions into built-up areas from 2016 to 2022.A noticeable reduction from 2019 to 2022 could be attributed to Covid-19 related restrictions, which otherwise might have resulted in a more significant escalation of built up areas.

Figure 6 .
Figure 6.Built-up distribution near the streams for the years 2016, 2019 and 2022.

Table 1 .
. Summary of datasets used in the study DEMStream Network ------Major streams in the region Strahler Order algoithm in SAGA of QGIS GeoTIFF

Table 2 .
Built up dynamic index calculation for different years

Table 3 .
LULC built-up area distribution as per elevation Year LULC Built up area distribution as per elevation (in metres)

Table 4 .
Urban sprawl as per elevation

Table 5 .
LULC built-up area distribution as per slope YearLULC Built up area distribution as per slope (in percentage)

Table 6 .
Urban sprawl as per slope

Table 7 .
Urban Sprawl near streams Around 55% increase in tourist footfall, both domestic and foreign, has been witnessed in the state of HP from 2008 to 2022, while an increase of 168% from 2021 to 2022 as per the statistics revealed by the Economics & Statistics Department, Government of HP.Around 168 hectares of forest area were lost HP from 2010 to 2022, equivalent to 78,800 metric tons of CO2 emissions as per Global Forest Watch.The unregulated tourism activity through the Himachal Pradesh Home Stay Scheme, 2008 has resulted in mushrooming of Homestays and the depletion of land resources.A 27% increase in the bed capacity registered under Himachal Tourism had been witnessed from 2017 to 2019.Further, the recent provisions in Forest Conservation Amendment Bill, 2023 which mandate the government to utilize forest land and non-classified forest land for non-forestry purposes will promote more environmental degradation in the name of development works and eco-tourism projects.A large scope and opportunity lies for hydroelectric power generation and tourismrelated service sectors in Himalayan regions, but should not be at the cost of environmental degradation and ecosystem imbalance.The Amendment Bill seeks exemption on forest land recorded as a "forest" but not notified as a "forest" before 1980.The sustainable development model is the need of the hour and certain legislative/ administrative reforms are required to prepare an action plan for the management and conservation of land resources.The increasing population and change in occupation can have serious implications for the city shortly.Dharmashala City recorded the highest population growth rate of 61% from 2001-2011