Climate change has various impacts on the world. One of these impacts is the occurrence of severe heat storms for extended durations during the summer. These events create intensely uncomfortable conditions in urban areas. In recent years, numerous scientific studies have been conducted to examine the nature, temperature variations, and patterns of change on a global scale, encompassing local, regional, and global levels (Khan and Chatterjee, 2019). The climatic changes observed in urban centers result from both natural processes and human-induced alterations to the Earth's surface and atmospheric properties (Henderson and Gornitz, 1984).
In the late 1950s, urban areas accounted for 30% of the global population, a percentage that grew to 55% by 2018 and is projected to reach 68% by 2050 (UN, 2014; UN, 2018). The global population grew only six times in the last 200 years, and the urban population increased 128 times (Schell et al., 1993). This rapid urbanization has significantly impacted society, the environment, and humanity as a whole. Urbanization has had a profound effect on urban societies and living standards. It has also placed substantial pressure on the environment to sustain the growing urban population. Numerous studies have highlighted that urbanization has been a driving force behind the social and economic development of urban centers, transforming them into efficient, convenient, and innovative marketplaces, albeit with consequences for surrounding suburban and rural areas (Seto et al., 2011; Cui and Shi, 2012; Liu and Diamond, 2005). These studies have shown that urbanization has led to increased demand for housing, resulting in subpar living conditions, inadequate housing, reduced natural vegetation due to decreased permeable surfaces, altered surface albedo, loss of biodiversity, increased water and air pollution, and diminished water supply (Ohwo and Abotutu, 2015; Hahs et al., 2009; Zhao et al., 2006; Cui and Shi, 2012). Additionally, it has altered land use and land cover patterns, modifying natural biogeochemical and water cycles, fragmenting natural habitats, leading to biodiversity loss, rapid depletion of productive farmland, and causing local weather variations due to changes in surface albedo (Seto et al., 2011; Radeloff et al., 2010; Jago-on et al., 2009; Yuan, 2008).
Urban development, combined with modifications to the lithosphere and atmosphere, has inadvertently resulted in climatic changes. Dense urban materials absorb heat and create impermeable surfaces, while tall buildings alter albedo, trapping more radiation, increasing air stagnation, and leading to heightened air pollution and the formation of Cloud Condensation Nuclei (CCN). Additionally, human activities release heat, further contributing to the urban heat environment (Oke, 1987).
This inadvertent impact of urbanization and climatic changes, along with infrastructural development, can render urban environments vulnerable. The Urban Heat Island (UHI) effect, has become a growing concern for urban climatologists (Doan and Kusaka, 2015). The UHI effect is characterized by elevated air temperatures in urban landscapes surrounded by cooler temperatures in suburban or rural areas. The heat island effect is most prominently noticed around the minimum temperature epoch, when the temperature curve is more or less flat (Bahl and Padmanabhamurty 1979; Gangadharan et al. 1999. Oke (1995) defined UHI as the temperature differences between the urban and surrounding rural stations. Urban Heat Island (UHI), a consequence of urbanization was first observed by (Howard, 1818; Oke, 1982). Numerous studies have indicated that various properties of the UHI are directly linked to the structural features of the urban landscape. As Bridgman et al. (1995) pointed out, "buildings impact the urban environment in five significant ways: by replacing vegetated areas, generating artificial heat, introducing block-like buildings, emitting pollutants, and draining rainfall rapidly."
In recent years, extensive research has been conducted on the UHI in diverse climate zones to investigate the UHI phenomenon's mechanisms and the impact of urbanization on UHI effects in cities (Doan and Kusaka, 2015). Most studies encompass urban modifications to local climate, such as UHI effects and changes in LULC, at an urban scale. This implies that urban temperatures tend to be higher in the urban core compared to its suburban natural surroundings, particularly at night (Oke and Cleugh, 1987; Arnfield, 2003; Parker, 2010).
Chen et al. (2014) identified factors contributing to the formation of Urban Heat Islands (UHI): (a) alterations in the land surface physics due to extensive urbanization, resulting in changes to urban albedo, thermal emissivity, and material conductivity; (b) human-induced heat generation from various activities; (c) reduced surface evapotranspiration caused by urban concretization; and (d) modifications in flow characteristics and near-surface atmospheric processes due to factors like a low sky view factor (SVF) and urban geometries (Kim and Baik, 2005). The ongoing development poses a threat to the conservation value of protected areas, potentially leading to a decline in biodiversity (Helmers, 2010). Urban regions experience heightened heat levels due to multiple factors, with some, such as climate and topography, beyond human control. However, there are two modifiable factors—vegetation quantity and surface color—that significantly contribute to the additional heat associated with human activities (Akbari, 2009).
Several studies have employed different approaches to represent urban climate and changes in Land Surface Temperature (LST), which can be categorized into ground-based and satellite observations. Traditional ground-based observations rely on weather stations to estimate variations in near-surface air temperature between rural and urban areas (Eludoyin et al., 2013; Vancutsem et al., 2010; Rao, 1972). Ground-based measurements require a significant number of weather stations within the study area to yield meaningful results. In contrast, satellite observations offer a more promising alternative, as they provide LST data at suitable temporal and spatial resolutions for studying UHI (Sobrino et al., 2012; Weng, 2009; Hamdi and Schayes, 2008; Qiao et al., 2013). Thermal infrared (TIR) imagery has been employed for detecting urban sprawl and UHI intensities (Landsat Project Science Office, 2002; Rao, 1972; Gallo et al., 1995). NDVI values serve as indicators of vegetation density, facilitating the assessment of changes in (LULC) patterns to analyze UHI intensities. Numerous studies have explored the relationship between vegetation density and LST, providing insights into estimating UHI intensity using Landsat data (Estoque et al., 2017; Bokaiea et al., 2016; Chen et al., 2006; Omran, 2012; Kawashima, 1994;).
Study area
Hyderabad is both the capital and the largest city of Telangana. The study area encompasses the region surrounding Hyderabad, situated at latitude 17° 16' 56'' to 17° 33' 40'' N and longitude 78° 14' 38'' to 78° 38' 28'' E, covering an area of 686 square kilometers (Fig. 1). Hyderabad is characterized by hilly terrain with numerous artificial lakes and is situated on the banks of Musi, which is a tributary of Krishna River. With a population of 6.9 million people (INDIA, 2011) it ranks as the fourth-most populous city in the country. Situated on a sloping terrain of pink and grey granite the city has an average altitude of 542 meters (Ramachandraia, 2013). Some of the notable artificial lakes in the area include Hussain Sagar, Osman Sagar, and Himayat Sagar.
Hyderabad experiences a tropical wet and dry climate. The region falls within the moderate (26°C-32°C) to strong heat stress (32°C to 38°C) range according to the Universal Thermal Climate Index. It maintains an annual average temperature of 26.6℃, with monthly average temperatures ranging between 21℃ to 33℃. Summers are characterized by hot and humid conditions, often exceeding 40℃ in May. The months of December and January are the coldest, with temperatures occasionally dropping to 10℃ (Norman et al., 1995). On June 2, 1966, Hyderabad recorded its highest temperature of 45.4℃, while the lowest temperature ever recorded was 6.1℃ on January 8, 1946.
The majority of Hyderabad's rainfall occurs during the southwest monsoon period between June and September. The heaviest 24-hour rainfall recorded was 241.5 mm on August 24, 2000 (IMD). Annually, the city receives 2,731 hours of sunshine, with the highest daily sunlight exposure occurring in February (Yimene and Minda, 2004).
Cloud cover varies throughout the year, with the months from June to October experiencing around 50% cloud cover, while January to March has significantly less at only 25%. Clear skies are often observed in January, February, and March. The monsoon months of July, August, and September are characterized by very high humidity levels exceeding 75%, while the months of March, April, and May are dry and experience lower humidity levels ranging from 25–30% (http://hyderabad-india-online.com/2011/06/climatic-conditions-hyderabad).
Wind patterns in Hyderabad vary by season, with southern winds prevailing for three months (February to April), western winds for four and a half months (mid-May to September end), and eastern winds for four months (October to January). Wind speeds are higher during the windier months of June, July, and August, with average speeds of 10 miles per hour, while the rest of the months experience calmer conditions with average wind speeds of 6.3 miles per hour (https://weatherspark.com/y/109450/Average-Weather-in-Hyderabad-India-Year-Round).