A critical review of Urban Heat Island phenomenon in the context of Greater Kuala Lumpur, Malaysia
Introduction
Rapid urban development and population growth in the tropical regions demonstrated an inextricable change from the natural environment which has brought about many health and environmental challenges at various scales, mainly in the form of Urban Heat Island (UHI) phenomenon (Roth, 2007; Tan, Lim, MatJafri, & Abdullah, 2009). Indeed, United Nation’s (UN) report highlighted that approximately three quarter of south-east Asian cities that host 53% of the world’s current urban population exhibit greater potential for a rapid urbanization by 2050, thus intensifying the eventual impacts of UHI in the region (UN (United Nations), 2014).
Being one of the vibrant tropical cities in the heart of south-east Asia, Malaysia is not exempted from experiencing a significant urban development that exacerbate the urban microclimate in terms of accelerated ambient air temperatures and associated implications. Recently, the urban heating phenomenon received a considerable attention from atmospheric scientists of Malaysia as the country was occasionally bombarded with many devastating consequences of rising temperatures such as flash flood (Akasah & Doraisamy, 2014), torrential rain (Gasim, Toriman, & Abdullahi, 2014), heat waves (Othman et al., 2016), chronic water shortages (Yew, 2014) and even rare episodes of hail storms (The Star, 2016). UN’s news report asserted that the mean global temperature of the first half of the year 2016 is 1.3 °C warmer than the late nineteenth century, setting 2016 as the hottest year ever on record (UN (United Nations), 2016). This is a consequential issue for GKL, which is a fast growing tropical urban conurbation owing to its crucial role as an engine of economic growth for Malaysia. In fact, a notable attention was garnered after the capital city of Kuala Lumpur (KL) was described as getting hotter by 0.6 °C per decade, which is the world’s highest value so far reported for the UHI effects until 2005 (Davis, Nordin, Ghazali, Durak, & Reimann, 2005). However, tracking urban heating phenomenon and the related consequences over the years is difficult due to unavailability of continuous measurements and studies in this region. While the earliest UHI studies in Malaysia go back to few decades ago (Sani, 1972, Sani, 1986), there is a discernible paucity in UHI assessments after Sani’s successive measurements between 1970 and 1990 in KL. A significant number of studies started to emerge only after a study by Elsayed, 2012a, Elsayed, 2012b, Elsayed, 2012c reported an increase of 1.5 °C of UHI Intensity (UHII) in KL in 2004 compared to a similar study conducted in 1985 (Elsayed, 2012c; Sani, 1986).
Based on the initial literature survey of UHI studies in GKL region, the inadequacy of field site reporting, poor statements on climate data homogenization, confusing statements of operational definitions of UHII, limited coverage of weather network and data collection and publication durations are identified as the main factors that decrease the authenticity and reliability of the previous assessments. This calls for a comprehensive technique to communicate the site characteristics and to record UHI magnitudes to enhance the assessment accuracy of future studies. Hence, this study aims to provide a state-of-the-art review of the UHI studies in the context of GKL by highlighting the existing methodological conflicts before providing recommendations and suggestions from the assessment perspectives to improve the reliability of future UHI assessments in Malaysia. This review starts by presenting a brief description of UHI and the nature of tropical UHI. Thereafter, a state-of-art review of UHI studies in GKL was presented. Finally, an evidence-based approach to address the methodological shortcomings of UHI studies in GKL was presented.
Section snippets
Concept of UHI
UHI phenomenon was first investigated and described in 1810s by Luke Howard, a British scientist who discovered that the city of London is warmer than the undeveloped rural surroundings (Roth & Chow, 2012). Starting from this point, the accumulation of anomalous heating in the vibrant cities started to draw the attention of urban climatologists as one of the most significant influence of human settlements on the earth’s climate (Nasir et al., 2015). Contextually, UHI phenomenon is a type urban
UHI status in the tropical cities
According to Arnfield (2003) UHI studies in the equatorial, tropical and sub-tropical settlements are still scanty while a remarkable accumulation of observational heat island studies presents in temperate climates. UHI phenomenon in the tropics, which is generally not well studied, is of importance as the region exhibits higher population growth and socio-economic and environmental significance. In fact, the nature of UHI is expected to rely on the geographical variations although their
GKL as a global city
GKL, a relatively new term as compared to the more established Klang Valley term, refers to a geographical region that comprises the national capital of KL and its surrounding satellite towns (EPU (Economic Planning Unit), 2010; Shaharuddin et al., 2014; Yusuf, Pradhan, & Idrees, 2014). Being close to the equator, it experiences a tropical rainforest climate which is characterized by an abundant rainfall and sunshine throughout the year (Aflaki et al., 2016). This urban agglomeration is
Methodological conflicts in UHI assessment in GKL
The reliability of the recorded UHII in the existing studies in GKL can only be defensible when clear statements of operational definitions of UHII, a proper system of field site reporting, removal of non-climatic fingerprints from the meteorological data, broader coverage of weather station network as well as timely and sufficient data are included in the previous assessments. As alluded by Stewart & Oke (2012), many local investigators also unequivocally relied on urban and rural air
Future prospects and new dimensions in UHI quantification for GKL
The urban-induced warming effects have higher tendency to create warm bias to the temperature pattern of historical climate series (Stewart & Oke, 2012). A proper justification on the extraneous heat effects triggered solely by urban transformation activities is essential for the climatologists to exclude such externalities that can contaminate the climate series data. Hence, a standardized guideline to address and report the urban characteristics of the local settings for temperature
Discussion
A concrete grasp of the issues that impose a significant alteration to urban microclimate is vital to develop more climate-friendly cities in Malaysia. Limited number of local studies in GKL hinder a proper understanding of the mechanism, factors, effects and remedies of UHI even though it is considered as the most documented phenomenon of climate change in the world. Furthermore, the available work is devoted towards descriptive studies that depict UHI magnitudes in the urban areas rather than
Conclusion: the way forward
This review presents an analysis of UHI studies conducted in GKL, the methodological shortcomings and the recommendations to enhance those problems in the future studies. While the available UHI studies are still scanty, the last decade has witnessed a mushrooming number of studies assessing the factors and mitigation of UHI in this region. The conventional use of urban-rural temperature discrepancies in UHI quantifications with measurements of the rural sites done near urban areas, improper
Acknowledgements
The authors would like to express their gratitude to the University of Malaya as this study is financially supported by University of Malaya Grand Challenges Research Grant (GC002A-15SUS).
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