The Effect of Plants on Extensive Green Roofs in Urban Heat Island Mitigation Efforts in Humid Tropical Cities

One of the urban heat island mitigation strategies in reducing urban temperatures in tropical cities is the application of a green roof system. This study compares the reduction in temperature and heat flow rate provided by three types of plants on extensive green roofs (EGR). We demonstrated that a EGR constructed with three types of plants (ground cover, and shrubs) could result in a decrease in temperature relative to the normal roof (NR). The results showed that the base temperature of the EGR of the bush and ground cover was lower than the base temperature of the NR which was 10.2ºC on indoor air, 17.8ºC on the inside and 19.1ºC on the outside. The peak indoor temperature was over 50ºC for the NR prototype. In the model with pennisetum purpureum schamach as the EGR, the maximum temperature was 40.1ºC, while for portulaca grandiflora and tradescantia spathacea the peaks were 37.6ºC and 37.5ºC, respectively. This shows that plants with large leaf widths are able to reduce heat greater than plants with small leaf widths.

Satellite and Ground Estimates of Surface and Canopy-Layer Urban Heat Island

The urban heat island (UHI) effect is one of the prominent impacts of urbanization that affects human health and energy consumption. As the data is limited and inconsistent, UHI comparative studies between UHIUCL and UHISurf on the seasonal scale are limited. The use of only daytime summer imagery reporting “Inverted UHI” undermines the holistic view of the phenomenon. Therefore, this study analyses the seasonal patterns for UHISurf and UHIUCL in three climate zones (Delhi, Pune, and Montreal). The three cities experience a high traditional night-time UHIUCL (Delhi 7°C, Pune 6°C, Montreal 1.89°C). Landsat captures a prominent daytime UHISurf (15°C) in Montreal with temperate climate and daytime inverted UHISurf (-4°C) for Delhi in summer. Seasonally, the night-time UHI is prominent in summer and monsoon for Delhi, summer and spring for Pune, and summer for Montreal. Due to UHI effect, the heatwaves can be more intense in semi-arid and tropical cities than temperate cities.

A Review of How Building Mitigates the Urban Heat Island in Indonesia and Tropical Cities

A consequence of urbanization was the intensification of urban heat islands, especially in tropical cities. There have been rapid developments in infrastructure that have displaced open spaces. Meanwhile, Indonesia has a tropical climate directly affected by climate change. A high priority has been placed on adaptation measures to address issues such as sea-level rise, increased extreme weather, and threats to ecosystems and biodiversity. There is still a lack of specific knowledge regarding tropical climate in urban areas. In this paper, the author examines how building and urban planning affect urban heat islands in the tropics. According to the review, early planning and building based on local weather data can reduce the energy consumption and minimize the UHI effect. Furthermore, a media campaign and early education should increase awareness about adaptation measures between governments and citizens. Based on the findings from this study, some recommendations are offered for future urban planning, especially for tropical climates, to reduce UHI effects.

Urban Growth and Heat in Tropical Climates

This research describes the change in temperatures across approximately 270 tropical cities from 1960 to 2020 with a focus on urban warming. It associates urban growth indicators with temperature variations in tropical climate zones (tropical rainforest, tropical monsoon, and tropical wet-dry savanna). Our findings demonstrate that over time while temperatures have increased across the tropics, urban residents have experienced higher temperatures (minimum and maximum) than those living outside of cities. Moreover, in certain tropical zones, over the study period, temperatures have risen faster in urban areas than the background (non-urban) temperatures. The results also suggest that with continuing climate change and urban growth, temperatures will continue to rise at higher than background levels in tropical cities unless mitigation measures are implemented. Several fundamental characteristics of urban growth including population size, population density, infrastructure and urban land use patterns are factors associated with variations in temperatures. We find evidence that dense urban forms (compact residential and industrial developments) are associated with higher temperatures and population density is a better predictor of variation in temperatures than either urban population size or infrastructure in most tropic climate zones. Infrastructure, however, is a better predictor of temperature increases in wet-dry savanna tropical climates than population density. There are a number of potential mitigation measures available to urban managers to address heat. We focus on ecological services, but whether these services can address the projected increasing heat levels is unclear. More local research is necessary to untangle the various contributions to increasing heat in cities and evaluate whether these applications can be effective to cool tropical cities as temperature continue to rise. Our methods include combining several different datasets to identify differences in daily, seasonal, and annual maximum and minimum temperatures.

A global review of urban pollinators and implications for maintaining pollination services in tropical cities

Pollinators provide essential ecosystem services worldwide, but dependence on biotic pollination is higher in the tropics, where urbanization is expected to impact biodiversity more severely. Here, we present a global review on urban pollinator studies with emphasis on the tropics. From the 308 published studies that included information on pollinator groups, only ~25 % were conducted in tropical regions, while ~65 % were carried out in the non-tropical northern hemisphere. This overall trend was similar for all the major insect pollinator groups, but not for vertebrates, which were overall less studied in both tropical and non-tropical regions. The effects of urbanization on tropical pollinators are diverse and complex and likely depend on the extent and type of urbanization, as well as the pollinator taxa studied. For both insect and vertebrate pollinators, the existing studies suggest that tropical cities can support generalist species tolerant of human activity, but the lack of studies hampers other general conclusions. The underrepresentation of pollinator studies in tropical cities undermines the value of urban biodiversity conservation in the most biodiverse regions of the world and highlights a missing opportunity. Since promoting urban biodiversity benefits both nature and people, it could be especially relevant in the Global South, where economic and social inequalities are severe and pollinator conservation may contribute to sustainability goals. In this context, initiatives that foster more international collaborations and research in the tropics are essential for a better understanding of the effects of urbanization and the value of pollinators in urban areas. Such knowledge can provide the basis for better urban planning strategies that contribute to the conservation of biodiversity and maintenance of pollination services in tropical cities.

Wolbachia-mediated sterility suppresses Aedes aegypti populations in the urban tropics

Incompatible insect technique (IIT) via releases of male Wolbachia-infected mosquitoes is a promising tool for dengue control. In a three-year trial in Singaporean high-rise housing estates, we demonstrated that Wolbachia-based IIT dramatically reduces both wildtype Aedes aegypti populations [reductions of 92.7% (95% CI: 84.7%-95.8%) and 98.3% (97.7%-99.8%)] and dengue incidence [reductions of 71% (43%-87%) to 88% (57%-99%)] in the targeted areas. The study highlights the need to ensure adequate vertical distribution of released males in high-rise buildings, address immigration of wildtype females from neighboring areas, and prevent and mitigate stable establishment of Wolbachia in field mosquito populations. Our results demonstrate the potential of Wolbachia-based IIT (supplemented with irradiation, in Singapore's context) for strengthening dengue control in tropical cities, where dengue burden is the greatest.

Nature-Based Solutions for Urban Sustainability: An Ecosystem Services Assessment of Plans for Singapore’s First “Forest Town”

Rapid urbanization in many parts of the world has increasingly put the environment under pressure, with natural landscapes cleared to make way for built infrastructure. Urban ecosystems, and the services that they provide, can offer nature-based solutions to the challenges of urbanization. There is increasing interest in better incorporating ecosystems into urban planning and design in order to deliver greater provision of ecosystem services and enhance urban liveability. However, there are few examples of built or proposed urban developments that have been designed specifically with ecosystem services in mind–partly because there are few modeling tools available to support urban planners and designers by informing their design workflows. Through using Singapore’s latest nature-centric town as a case study, this article assesses the impacts of nature-based solutions in urban design on ecosystem services performance, through a spatially explicit modeling approach. The proposed future scenario for the nature-centric town was projected to result in substantial declines in the provision of all ecosystem services, as a result of the removal of large areas of natural vegetation cover. However, the future scenario compared favourably against three older towns that have been constructed in Singapore, showing the best performance for four out of six ecosystem services. This simulation exercise indicates that designing towns with ecosystem services in mind, and incorporating nature-based solutions into urban design, can help to achieve enhanced performance in providing ecosystem services. The models developed for this study have been made publicly available for use in other tropical cities.

Quantifying the impacts of urban gullying at the scale of the Democratic Republic of Congo

<p>Urban gullies cause major infrastructural damages and often claim casualties in many tropical cities of the Global South. Nonetheless, our understanding of this hazard currently remains limited to some case studies, while the impacts at larger scales remain poorly quantified. Here, we aim to bridge this gap by making a first assessment of the number of persons and buildings affected by urban gullies at the scale of the Democratic Republic of Congo (DRC). We used Google Earth imagery in combination with local news sources and earlier research to identify 25 cities in DRC where urban gullies occur at a significant scale (at least ten urban gullies). This list is likely exhaustive. Next, for each of these cities, we used Google Earth and other high resolution images to map all visible urban gullies, evaluate their expansion rate and inventorize detectable damages to houses and roads. In total, more than two thousand urban gullies were mapped across the 25 affected cities.  Overall, the problem of urban gullies in DRC is especially acute in the cities of Kinshasa, Mbujimayi, Tshikapa, Kananga, Kabinda, and Kikwit. Over 80% of these gullies were active during the observation period (typically from 2002 to 2020). We identified 4257 houses and 998 roads that were destroyed because of the formation and expansion of urban gullies. Nonetheless, the actual impacts are likely much larger since the limited amount of imagery available does not allow quantifying all impacts. For example, in most cases, a large urban gully was already present on the earliest image available.</p><p>We also made an estimate of the total number of persons that are directly affected, as well as the number of persons currently at risk. Using high resolution estimates of population density and taking into account the current position of urban gullies, we estimate that a total of 133000 people have already lost their house due to formation and expansion of urban gullies. Given that these gullies are typically less than 30-years old, we estimate that on average, at least 4000 people/year lose their house as a result of urban gullies in DRC. This may still be an underestimation. By considering the population that lives in the direct vicinity (<100 m) of an urban gully, we estimate that around 1.2 million people in D.R. Congo are currently at risk and/or experience significant impacts because of urban gullies (e.g. reduced land value, problems with trafficability, stress). An estimated 449000 persons live less than 100 m away from a gully head (which is typically the most active part of the gully) and are therefore likely at high risk to be significantly affected by urban gullies in the coming years.</p><p>Overall, this research shows that urban gullying is a very serious problem in the DRC, but likely also in many other tropical countries. More research is needed to better understand this processes and, ultimately, to prevent and mitigate its impacts. The results and the database of this study provide an important step towards this.</p>