Elsevier

Urban Climate

Volume 29, September 2019, 100482
Urban Climate

Future urban climate projection in a tropical megacity based on global climate change and local urbanization scenarios

https://doi.org/10.1016/j.uclim.2019.100482Get rights and content

Highlights

  • Effects of present and future urbanization scenarios on climate change.

  • Urbanization and climate change scenarios based on globally available inputs.

  • Background future global climate affected temperature change homogenously.

  • Local urban effects varied significantly based on the location of urban expansion.

Abstract

The effects of urbanization on the future atmospheric environments of cities worldwide remain uncertain in the context of climate change. We introduce a general method for modeling the effects of climate change and urbanization that can be applied to any city and apply the model to Greater Jakarta megacity. Global climate change scenarios (RCP2.6 and RCP8.5) were coupled with distributed urbanization scenarios (compact and business-as-usual (BaU), based on projections of future urban morphology and anthropogenic heating) in a mesoscale weather model. Despite the predominant influence of global effects, the urban effects of individual grids were spatially varied. The highest temperature increase caused by RCP8.5&BaU scenario was detected in the northwestern outskirts of Jakarta. Meanwhile, the projected temperature was one-third lower in the RCP2.6&Compact scenario. Overall, this study offers a general method for projecting future urban climates, not only for Jakarta but also for other megacities in developing countries.

Introduction

Future climate change is expected to increase the vulnerability of urban populations to associated risks, which are further exacerbated in low- and middle-income countries (Revi et al., 2014). Moreover, urban agglomerations have local effects on the atmosphere (Arnfield, 2003; Masson, 2000; Oke et al., 2017) that could intensify the effects of global climate change. For example, from 1961 to 2010, the mean annual temperatures in 39 major cities increased at rates of 0.12–0.45 °C per decade (Rosenzweig et al., 2015). Meanwhile, urban areas have been projected to be warmer than surrounding rural areas (Kalnay and Cai, 2003) and are projected to experience more tropical nights in the future (McCarthy et al., 2010; Oleson, 2012) under climate change. Such urban effects will have a significant impact on energy consumption for cooling (Martilli, 2014), heat waves (Anderson et al., 2018; Lemonsu et al., 2015; Wouters et al., 2017; Zhao et al., 2018), sea breeze penetration (Varquez et al., 2014), and urban extreme rainfall (Niyogi et al., 2017).

Until recently, general circulation models could not capture urban effects due to their coarse spatial and temporal resolutions (Best, 2006). These models either did not include or roughly assumed urbanization in their future projections. However, recent advances in mesoscale climate modeling have enabled the analysis of urban effects under climate change, although most relevant studies have been conducted at city scales (Doan et al., 2019; Doan et al., 2016; Hamdi et al., 2014; Lemonsu et al., 2015), with very few focused on a global scale (Fischer et al., 2012; Oleson et al., 2011). The results of these studies have revealed that urban areas are expected to experience greater temperature increases than surrounding rural areas under a given future climate change scenario. However, such studies have been limited to the assumption that future urban land use is static to present conditions. In reality, urban expansion in developing countries is expected to accelerate in the near future. Therefore, projecting the future urban climate solely based on climate change effects under the assumption of a static urban area is unrealistic.

Application of urban growth controls (Georgescu et al., 2014; Stone et al., 2010) and urban fabric modifications (Georgescu, 2015; de Munck et al., 2018) to weather models has shown that urban adaptation strategies determine the magnitude of urban effects, indicating that sound urban planning is necessary to achieve highly resilient cities. Recent studies have highlighted the behavior of urban effects under climate change and future urban expansion scenarios in cities of American (Li et al., 2016; Tewari et al., 2017), European (Hamdi et al., 2014; Wouters et al., 2017), Asian (Adachi et al., 2012; Yang et al., 2016), and Australian (Argüeso et al., 2015). The results have shown that due to background temperature increases local urban effects cause greater warming than under global future climate scenarios. However, these studies limited urban expansion to practical urbanization scenarios or two-dimensional urban land-use scenarios with simple parameterizations of urban morphology. By contrast, few advanced studies have coupled future global climate change scenarios and local urbanization based on socio-economic scenarios (Kusaka et al., 2016; Masson et al., 2014). Such studies excel in the projection of future urban morphological parameters and heat emissions based on socio-economic scenarios. Despite these studies representing future urban climates more realistically, they have been restricted to developed countries and their study areas. More recent studies analyzed urban climate by combining global climate change scenario and local urbanization based on issued urban development master plan in developing countries (Doan et al., 2019; Doan et al., 2016; Iizuka, 2018; Lee et al., 2017; Yang et al., 2016). However, it is very challenging to get such urban planning data in global scale.

To address this shortcomings, we developed a future urban climate projection by integrating global climate change projection based on pseudo global warming method and local urbanization scenario based entirely on globally available datasets. Compared with previous similar studies, our goal is to develop a local urbanization scenario considering building volumes and heat emission derived from global socio-economic scenario. We aversely using any data from local governments or stakeholders to optimize global implementation. The framework was designed to provide a generic, repeatable, and realistic approach to futuristic urban climate studies. We applied the method to project the future urban climate in Greater Jakarta, Indonesia, as a large tropical megacity in Southeast Asia, until the 2046–2055. We integrated Representative Concentration Pathways (RCP; van Vuuren et al., 2011) and urbanization scenario derived from Shared Socioeconomic Pathways (SSP; O'Neill et al., 2014) in mesoscale weather simulations. Accordingly, we were able to analyze the global, urban, and combined global–urban effects. The ultimate goal is that this approach can be applied to other megacities in developing countries.

Section snippets

Methodology

Two global emission scenarios of RCP, RCP2.6 and RCP8.5 were selected considering the best and worst emission scenario respectively. We paired RCP with SSP to include local urbanization adaptation scenario thus creating an integrated global-urban climate projection analysis. We used SSP1 and SSP3 scenario generated from Integrated Assessment Model of Asia Pacific Integrated Model (AIM) globally available at regional and country scale (Fujimori et al., 2012, Fujimori et al., 2017). RCP scenario

Present climate validation

Validation was performed using 2006–2015 observation data from three World Meteorological Organization-standardized urban stations located within the target domain: Kemayoran station (KMO), Tanjung Priok station (TPR), and Cengkareng station (CGK), with 3-hourly data taken from ogimet.com (see Appendix A1). The model predicted the nighttime temperature well, with root mean square error (RMSE) values of 1.03, 1.14, and 1.45 for TPR, KMO, and CGK, respectively. However, the model generally

Discussion

The findings of this study imply that the effect of combined climate change and local urbanization is highly varied at a 1-km resolution, despite the overall small average values. It is apparent that the future urban climate is approximately a linear sum of future global climate change and local urbanization effect, which agrees with similar previous studies (Doan and Kusaka, 2018; Lee et al., 2017). The urbanization effect itself strongly related to how urban parameters and AHE change in the

Conclusion

Projections of the future climate of tropical, rapidly urbanizing megacities cannot rely solely on the effects of emission scenarios. The results of this study imply that urban effects can reach the same magnitude as global effects. Even though urban signals dominated the climate signal by an average factor of 12.2 (13.0) under the RCP2.6&Compact (RCP8.5&BaU) scenario, the findings showed that the urban signal distribution values were highly and significantly spatially diverse. In order to

Acknowledgement

This research was supported by the Environment Research and Technology Development Fund (S-14) of the Ministry of the Environment, Japan. We are grateful to Shinichiro Fujimori and AIM/CGE team, Center for Social and Environmental Systems Research, National Institute for Environmental Studies, Tsukuba, Japan for providing the AIM/CGE model for Indonesia (http://www.nies.go.jp/social/dp/pdf/2012-01.pdf). Global AHE data with a 1-h temporal resolution and 1-km spatial resolution can be downloaded

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