A Case Study of Kurunegala, Sri Lanka
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International Journal of Geo-Information Article Spatiotemporal Variation of Urban Heat Islands for Implementing Nature-Based Solutions: A Case Study of Kurunegala, Sri Lanka Manjula Ranagalage 1,2,* , Sujith S. Ratnayake 3,4, DMSLB Dissanayake 1 , Lalit Kumar 4 , Hasula Wickremasinghe 3, Jagathdeva Vidanagama 5, Hanna Cho 6, Susantha Udagedara 7 , Keshav Kumar Jha 8, Matamyo Simwanda 9 , Darius Phiri 9 , ENC Perera 10 and Priyantha Muthunayake 11 1 Department of Environmental Management, Faculty of Social Sciences and Humanities, Rajarata University of Sri Lanka, Mihintale 50300, Sri Lanka; [email protected] 2 Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8572, Japan 3 Climate Change Secretariat, Ministry of Environment and Wildlife Resources, Battaramulla 10120, Sri Lanka; [email protected] (S.S.R.); [email protected] (H.W.) 4 Ecosystem Management Division, School of Environmental and Rural Science, University of New England, Armidale, NSW 2350, Australia; [email protected] 5 Department of Zoology and Environment Sciences, Faculty of Science, University of Colombo, Colombo 10120, Sri Lanka; [email protected] 6 Korea Environment Institute, 5F, Bldg B, 232, Gareum-ro, Sejong 30121, Korea; [email protected] 7 Blue Resources Trust, 86, Barnce Place, Colombo 00700, Sri Lanka; [email protected] 8 ICLEI-Local Governments for Sustainability, South Asia, vC-3, Lower Ground Floor, Green Park Extension, New Delhi 110016, India; [email protected] 9 Department of Plant and Environmental Sciences, School of Natural Resources, Copperbelt University, P.O. Box 21692, Kitwe 10101, Zambia; [email protected] (M.S.); [email protected] (D.P.) 10 Department of Regional Science and Planning, SANASA Campus, Kegalle 71000, Sri Lanka; [email protected] 11 Municipal Council, Kurunegala 60000, Sri Lanka; [email protected] * Correspondence: [email protected] Received: 28 May 2020; Accepted: 14 July 2020; Published: 21 July 2020 Abstract: Changes in the urban landscape resulting from rapid urbanisation and climate change have the potential to increase land surface temperature (LST) and the incidence of the urban heat island (UHI). An increase in urban heat directly affects urban livelihoods and systems. This study investigated the spatiotemporal variation of the UHI in the Kurunegala urban area (KUA) of North-Western Province, Sri Lanka. The KUA is one of the most intensively developing economic and administrative capitals in Sri Lanka with an urban system that is facing climate vulnerabilities and challenges of extreme heat conditions. We examined the UHI formation for the period 1996–2019 and its impact on the urban-systems by exploring nature-based solutions (NBS). This study used annual median temperatures based on Landsat data from 1996 to 2019 using the Google Earth Engine (GEE). Various geospatial approaches, including spectral index-based land use/cover mapping (1996, 2009 and 2019), urban-rural gradient zones, UHI profile, statistics and grid-based analysis, were used to analyse the data. The results revealed that the mean LST increased by 5.5 ◦C between 1996 and 2019 mainly associated with the expansion pattern of impervious surfaces. The mean LST had a positive correlation with impervious surfaces and a negative correlation with the green spaces in all the three time-points. Impacts due to climate change, including positive temperature and negative rainfall anomalies, contributed to the increase in LST. The study recommends interactively applying NBS to addressing the UHI impacts with effective mitigation and adaptation measures for urban sustainability. ISPRS Int. J. Geo-Inf. 2020, 9, 461; doi:10.3390/ijgi9070461 www.mdpi.com/journal/ijgi ISPRS Int. J. Geo-Inf. 2020, 9, 461 2 of 21 Keywords: LST; UHI; impervious surface; green surface; climate change; NBS; Kurunegala; Sri Lanka 1. Introduction Sri Lanka has shown stable economic growth over the last few decades, which has led to the country being categorized as an upper-middle-income country in 2018 [1]. From 1960 to 2018, the otal population of Sri Lanka increased by 11.8 million (119.5%) [2], while the urban population also increased by 2.4 million (146.8%) [3]. Additionally, Sri Lanka has experienced rapid economic growth after 30 years of civil war that ended in 2009, with a 5.6% economic development between 2010 and 2018 [4]. As the centre of the South Asian region, Sri Lanka is considered as a central node in the proposed “21st Century Maritime Silk Road” [5]. The central location of the country is directly impacted by rapid mega-development projects such as megacity expansion, airports, harbours, urban beautification and highways, especially during the last ten years [6]. The last decade has seen most of the expressways construction and development projects such as Southern, Outer Circular, Colombo-Katunayake and Andarawewa-Hambantota that were implemented to enhance the economic development of the country [7,8]. This rapid development of the transportation systems resulted in increasing urbanisation, which has a direct impact on the urban population of up to 4.0 million (18% of the total population). However, the negative impacts associated with urbanisation have increased during the past few decades [9]. Urbanisation provides socio-economic development; however, this development has negative impacts on natural environments [10]. The rapid increase of the urban population, increased use of grey infrastructure, high energy usage, conversion of agricultural land to industrial sites together with high environmental pollution levels have directly affected the urban ecosystem health and human wellbeing in Sri Lanka [11]. During the past few decades, most of the green areas and wetlands in urban and peri-urban areas in Sri Lanka have been converted to impervious surfaces (IS) [12]. These rapid conversions have resulted in several negative impacts, such as air pollution [13], decreasing green surface (GS) [9], declining agricultural lands [14,15], increasing vector-borne diseases [16], water pollution [17], declining wetlands [18] and increasing Urban Heat Island (UHI) [19]. The UHI is a phenomenon that refers to the aspect that urban areas are warmer compared to rural surroundings [20]. In other words, a UHI refers to an urban region that is altogether hotter than its surrounding rural regions due to human activities. The daytime and night-time surface temperature differences between developed and rural areas have been reported to range from 10 ◦C to 15 ◦C and 5 ◦C to 10 ◦C, respectively [20]. The UHI exists regardless of city size, although, its magnitude varies depending on the size of the city [20]. There are several negative impacts associated with UHI in urban areas. These include energy balance changes [21], heat-related human illness and discomfort [20], increasing air pollutants [20], impaired water quality [20] and increased mortality among older people [22]. In addition, the increase of the ambient temperature due to the UHI has a direct impact on increasing the Green House Gas (GHG) emissions associated with energy use in the buildings [23–25]. As a result of these effects, UHI has now become an urgent research topic [26]. The UHI can be calculated based on air temperature and land surface temperature (LST) [20]. However, conducting UHI studies by using air temperature is challenging, especially in developing countries where meteorological stations and ground-based data are lacking or sparse [20]. Thus, UHI studies based on land surface temperature (LST) derived from remote sensing (RS) data have become common among researchers due to its spatial extent and temporal availability [27]. The rapid development of RS data and geospatial analysis has significantly enhanced UHI studies during the past three decades [28,29]. Past studies have mainly used the relationship between mean LST and two primary land use/cover (LULC) types (i.e., impervious surfaces (IS) and green spaces (GS)) to understand the UHI effect in several cities such as mountainous cities [9,30], coastal cities [26,31] and inland cities [31–33]. There are several approaches for the extraction of land use/land cover (LULC) ISPRS Int. J. Geo-Inf. 2020, 9, 461 3 of 21 information such as pixel- and object-based [34,35] and spectral index-based methods. Among these methods, the spectral index-based method has been proven to be the most effective [26,31,36,37] especially in recent UHI studies [19,31,32]. On the other hand, to have a comprehensive understanding of the UHI distribution various approaches have been used. For example, to understand the temperature difference between the urban and rural zones, the urban-rural gradient analysis has been employed by several studies [30,31,38]. However, due to the inability to capture the directional deviation of the UHI through gradient analysis, other researchers employ the multitemporal and multidirectional UHI profile analysis over the orthogonal and diagonal directions of their respective cities [30,32]. Other previous studies have, additionally, employed the grid-based method to understand the relationship between LST and the fraction of IS and GS in their cities [26,39,40]. The UHI is considered as one of the byproducts of rapid urbanisation, and many mitigation methods have been studied and proposed by previous researchers. Some of the mitigation methods that have been proposed include (i) increasing vegetation cover; (ii) creating green roofs; (iii) use of cool roofs; (iv) use of cool pavements; and (v) smart growth by protecting the natural environment in urban areas [20,41–43]. Among these mitigation measures proposed, green infrastructure can be easily implemented in urban areas [44]. Green cover reduces air temperature [45] and decreases the surface temperature in urban areas [46]. Thus, natural ecosystems can be used to provide benefits to the urban climate and environments by increasing street trees, green walls and green roofs [44]. Nature-based solutions (NBS) have been identified as a key possible solution to mitigate the UHI in developing counties, more especially in small cities.