Tropical Urban Research Articles

Heavier Precipitation in Response to Longer-Lasting Tropical Cyclones and Rapid Urbanization over the Yangtze River Delta of Eastern China

Abstract Precipitation induced by tropical cyclones (TCs) over cities is associated with both TC duration and urbanization; however, observational evidence of the impacts of TC duration and urbanization on precipitation in megalopolises is limited. In this study, the Yangtze River Delta (YRD) of eastern China is taken as a typical region because this region has been experiencing both rapid urbanization processes and frequent TC attacks. During 1979–2018, we find reduced translation speed and increased meandering of TCs over the YRD, resulting in increased TC duration and the proportion of TC stalling in this region. The correlation between TC duration and TC-induced precipitation amount is significant across the YRD region but is relatively weak in areas with faster urbanization expansion rates. Long-term increases in TC-induced precipitation are found in both rural and urban areas but are larger for urban areas. Urbanization plays an important role in enhancing TC-induced precipitation over urban areas of the YRD region. Areas with faster urbanization expansion rates and longer TC durations have larger TC-induced precipitation, suggesting that urban expansion and TC duration jointly amplify TC-induced precipitation. Our findings suggest that urban planners, in areas potentially affected by TCs, should consider adaptation measures to mitigate the impacts of urban rainstorms amplified by the combined effects of TCs and urbanization. Significance Statement The combined impacts of tropical cyclone (TC) duration and urbanization on precipitation have received limited attention, especially in populated urban areas. Here, we focus on the Yangtze River Delta (YRD) of eastern China, an urban agglomeration frequently impacted by TCs. We find that slowed translation and increased meandering of TCs have led to longer TC duration and stalling over the 500-km YRD buffer during 1979–2018. Significant positive correlation between TC duration and TC-induced precipitation indicates that longer-lasting TCs trigger greater precipitation. The greater TC-induced precipitation due to increased TC duration is further amplified by urban expansion.

The Dynamics of Soil Mesofauna Communities in a Tropical Urban Coastal Wetland: Responses to Spatiotemporal Fluctuations in Phreatic Level and Salinity

Coastal wetlands, vital for ecological diversity, have been significantly altered by anthropogenic activities, particularly in the Caribbean. These changes have created a complex mosaic of habitats and physicochemical conditions, further stressed by climate variability and sea-level rise. This study, conducted in Las Cucharillas Natural Reserve, a tropical urban coastal wetland in Puerto Rico, aimed to determine the effects of spatiotemporal variations in phreatic levels and salinity on soil mesofauna assemblages, crucial bio-indicators of environmental change. In 2020 and 2021, soil samples were collected from five diverse habitat types during different hydroperiods. Each sample was taken under four randomly selected plant types and processed using lighted Tullgren–Berlese extractors. Phreatic level and salinity were also measured. A total of 43 families were quantified, underscoring distinct habitat differences, similarities, and overall ecosystem diversity. Moderate correlations between phreatic levels, salinity, and mesofauna richness and abundance were determined. Peak richness and abundance were quantified at shallow (−0.03 to −0.07 m) and slightly moderate (−0.12 to −0.17 m) phreatic levels where oligohaline salinity (>0.5 to 5.0 ppt) prevails. The study highlights the adaptability of mesofauna to environmental shifts and their potential as biosensors for effective coastal wetland management amid climatic and anthropogenic pressures.

Bayesian regression versus machine learning for rapid age estimation of archaeological features identified with lidar at Angkor

Lidar (light-detection and ranging) has revolutionized archaeology. We are now able to produce high-resolution maps of archaeological surface features over vast areas, allowing us to see ancient land-use and anthropogenic landscape modification at previously un-imagined scales. In the tropics, this has enabled documentation of previously archaeologically unrecorded cities in various tropical regions, igniting scientific and popular interest in ancient tropical urbanism. An emerging challenge, however, is to add temporal depth to this torrent of new spatial data because traditional archaeological investigations are time consuming and inherently destructive. So far, we are aware of only one attempt to apply statistics and machine learning to remotely-sensed data in order to add time-depth to spatial data. Using temples at the well-known massive urban complex of Angkor in Cambodia as a case study, a predictive model was developed combining standard regression with novel machine learning methods to estimate temple foundation dates for undated Angkorian temples identified with remote sensing, including lidar. The model’s predictions were used to produce an historical population curve for Angkor and study urban expansion at this important ancient tropical urban centre. The approach, however, has certain limitations. Importantly, its handling of uncertainties leaves room for improvement, and like many machine learning approaches it is opaque regarding which predictor variables are most relevant. Here we describe a new study in which we investigated an alternative Bayesian regression approach applied to the same case study. We compare the two models in terms of their inner workings, results, and interpretive utility. We also use an updated database of Angkorian temples as the training dataset, allowing us to produce the most current estimate for temple foundations and historic spatiotemporal urban growth patterns at Angkor. Our results demonstrate that, in principle, predictive statistical and machine learning methods could be used to rapidly add chronological information to large lidar datasets and a Bayesian paradigm makes it possible to incorporate important uncertainties—especially chronological—into modelled temporal estimates.

Urbanization alters the spatiotemporal dynamics of plant-pollinator networks in a tropical megacity.

Urbanization is a major driver of biodiversity change but how it interacts with spatial and temporal gradients to influence the dynamics of plant-pollinator networks is poorly understood, especially in tropical urbanization hotspots. Here, we analysed the drivers of environmental, spatial and temporal turnover of plant-pollinator interactions (interaction β-diversity) along an urbanization gradient in Bengaluru, a South Indian megacity. The compositional turnover of plant-pollinator interactions differed more between seasons and with local urbanization intensity than with spatial distance, suggesting that seasonality and environmental filtering were more important than dispersal limitation for explaining plant-pollinator interaction β-diversity. Furthermore, urbanization amplified the seasonal dynamics of plant-pollinator interactions, with stronger temporal turnover in urban compared to rural sites, driven by greater turnover of native non-crop plant species (not managed by people). Our study demonstrates that environmental, spatial and temporal gradients interact to shape the dynamics of plant-pollinator networks and urbanization can strongly amplify these dynamics.

Optimization of Technical Parameters for Detecting Mycobacteria in Hospital Wastewater in Tropical Urban Areas: The Case of the City of Abidjan (Côte d’Ivoire)

Optimization of Technical Parameters for Detecting Mycobacteria in Hospital Wastewater in Tropical Urban Areas: The Case of the City of Abidjan (Côte d’Ivoire)

Plant Diversity along an Urbanization Gradient of a Tropical City

This study aimed to investigate the plant diversity, plant traits, and environmental variables along the tropical urbanization gradient in Ipoh, Perak, Malaysia. The study areas comprised 12 sampling plots sized 1 km2 that represented different urbanization intensities. Urbanization intensity was quantified as the percentage of the built-up area within a 1 km2 area. A total of 96 woody plant species belonging to 71 genera and 42 families were found in the study areas. In general, species diversity, richness, and evenness declined significantly as urbanization intensity increased. The number of native species reduced by 67.6% when urbanization intensity increased from wildland to suburban while the non-native species remained stable along the urbanization gradient. Regarding the plant traits, tree height decreased with increasing urbanization intensity, while no significant result was found for specific leaf areas. All environmental factors were significantly associated with urbanization where air temperature and light intensity showed a positive relationship with increasing urbanization intensity while the opposite trend was found for air humidity. This study emphasizes the importance of built-up areas as the predictor of native species in the tropics. The findings of this study may help town planners and policymakers to create more sustainable urban development in the future.

Incorporating Ecological Constraints into the Simulations of Tropical Urban Growth Boundaries: A Case Study of Sanya City on Hainan Island, China

The rapid expansion of cities in tropical regions has triggered a series of problems such as the destruction of rare natural resources and decreases in the environmental resource carrying capacity and ecological security, which seriously threaten the sustainable development of tropical cities. In this study, the city of Sanya, Hainan, China, is taken as an example. A bottom-line ecological security pattern is constructed based on the remote sensing ecological index (RSEI) and the patch-generating land use simulation (PLUS) for urban growth boundary (UGB) delineation. The results show that Sanya has a good ecological background, but the overall ecological quality decreased from 2014 to 2018 due to the expansion of construction in hot spot areas. Under the natural growth scenario, the urban built-up area in Sanya in 2030 will be 73.81% greater than in 2018, mainly occupying a large amount of agricultural and ecological space, and urban expansion will not be effectively suppressed. Delineation of the UGBs combined with the ecological constraints can effectively protect the regional ecological security and control the urban sprawl, which is relatively consistent with the current planning. The results of this study demonstrate that the RSEI-PLUS-based UGB delineation perspective has a high scientific and applicability, and they provide a reference for the coordinated ecological–economic sustainable development of ecologically fragile cities in tropical areas.

Avian species richness and tropical urbanization gradients: Effects of woodland retention and human disturbance.

Urbanization is a major driver of tropical biodiversity loss. In temperate regions avian species richness–urbanization intensity relationships typically exhibit unimodal patterns, with peak richness at intermediate urbanization levels. In tropical regions, the form of such relationships and the extent to which they are moderated by patches of seminatural habitat are unclear. We address these questions in Bangkok, Thailand (one of the largest and most rapidly expanding tropical mega‐cities) and generate conservation recommendations for tropical biodiversity in urban locations. We use repeated point count surveys at a random location, and the largest available woodland patch, in 150 1 km × 1 km grid cells selected along the urbanization gradient. Woodland patches support higher species richness compared with randomized locations (except for non‐natives), and avian species richness declines linearly with increasing urbanization. The contrast with unimodal patterns in temperate regions is probably driven by divergent patterns of habitat heterogeneity along tropical and temperate urbanization gradients. Moreover, we provide novel evidence that retaining patches of urban woodland moderates adverse impacts of urbanization on avian species richness. For most species groups, the benefits of woodland increase as urbanization intensifies, despite such woodland patches being very small (mean of 0.38 ha). Avian species richness in woodland patches is maximized, and community composition less similar to that in randomized locations, when woodland patches are larger and visited by fewer people. Assemblages of forest‐dependent species (which provide additional ecological functions) have higher richness, and are less similar to those in randomized locations, in patches of woodland with higher tree species richness and biomass. Finally, species richness in randomized sites is greatest when they are closer to woodland patches, and such assemblages more closely resemble those of woodland sites. Our work highlights four strategies for tropical urban bird conservation: (1) conserving woodland patches across the urbanization gradient regardless of patch size, (2) improving the quality of existing woodland by increasing tree biomass and diversity, (3) creating additional woodland that is well distributed throughout the urban area to minimize effects of habitat isolation and (4) reducing human disturbance, especially in areas of the highest habitat quality, while ensuring that the benefits of connecting people to nature are realized in other locations.

The Impact of Vegetation Arrangement on Outdoor Thermal Comfort: A Simulation Study in a Tropical Urban Public Square

Thermally comfortable urban squares attract people and provide various social benefits to the urbanites. Compared to urban parks, squares are more vulnerable to thermal discomfort due to surrounding buildings and the high percentage of hard surface coverage, especially in tropical climates. The spatial arrangement of green infrastructures can improve Outdoor Thermal Comfort (OTC) by reducing hot air flows, evapotranspiration, and shading to reduce the negative effect of warming urban environments. However, it is not yet adequately discovered the specific correlation of different vegetation arrangements on OTC. Still, urban policymakers are looking for new, quantitative methods to assess the performance of their designs in terms of the cooling effects provided by vegetation. Therefore, the current study investigates the effect of different vegetation arrangements on OTC in a tropical urban public square (Independence Arcade in Colombo) using micrometeorological fluid dynamics (CFD) modeling validated by field measurements. Air temperature (Ta), relative humidity (RH), wind speed (WS), and wind direction (WD) were measured at 1.5 m above ground level as the inputs for the ENVI-met simulation model to assess the cooling performance of proposed scenarios employing Physiological equivalent temperature (PET). Nine scenarios were developed using trees with high leaf area density (LAD) and spherical canopy form to compare OTC improvements of cluster, random and individual planting patterns, and the size of trees (large, medium, small). The results showed that vegetation improves the OTC levels irrespective of the planting pattern. However, linear individual planting pattern with large trees performed the best cooling performance, and scenarios were ranked according to improved PET values. Vegetation parameters are recommended to arrange in different ways to achieve OTC and aesthetics. The study was limited to the existing vegetation database of the ENVI-met software package, but further research could consider the context-specific tree species and the impact of combined landscape scenarios using grass, shrub coverage, and water bodies to find proper arrangements to improve the microclimate and OTC. This study guides urban planners and landscape architects to assess the cooling performance of the proposed designs and arrange urban vegetation to create thermally comfortable urban outdoors in the tropics. 
 Keywords: Vegetation arrangement, Urban square, Outdoor thermal comfort, ENVI-met, PET
 Acknowledgement: Authors acknowledge the assistance of the Accelerating Higher Education Expansion and Development (AHEAD)-DOR Grant, funded by the World Bank

Lidar reveals pre-Hispanic low-density urbanism in the Bolivian Amazon

Archaeological remains of agrarian-based, low-density urbananism1–3 have been reported to exist beneath the tropical forests of Southeast Asia, Sri Lanka and Central America4–6. However, beyond some large interconnected settlements in southern Amazonia7–9, there has been no such evidence for pre-Hispanic Amazonia. Here we present lidar data of sites belonging to the Casarabe culture (around ad 500 to ad 1400)10–13 in the Llanos de Mojos savannah–forest mosaic, southwest Amazonia, revealing the presence of two remarkably large sites (147 ha and 315 ha) in a dense four-tiered settlement system. The Casarabe culture area, as far as known today, spans approximately 4,500 km2, with one of the large settlement sites controlling an area of approximately 500 km2. The civic-ceremonial architecture of these large settlement sites includes stepped platforms, on top of which lie U-shaped structures, rectangular platform mounds and conical pyramids (which are up to 22 m tall). The large settlement sites are surrounded by ranked concentric polygonal banks and represent central nodes that are connected to lower-ranked sites by straight, raised causeways that stretch over several kilometres. Massive water-management infrastructure, composed of canals and reservoirs, complete the settlement system in an anthropogenically modified landscape. Our results indicate that the Casarabe-culture settlement pattern represents a type of tropical low-density urbanism that has not previously been described in Amazonia.

Transitory Courtyards as a Feature of Sustainable Urbanism on the East African Coast

The tropical urbanism of coastal East Africa has a thousand-year-long history, making it a recognized example of sustainable urbanism. Although economically dependent on trade, the precolonial Islamic towns of the so-called Swahili coast did not feature markets or other public buildings dedicated to mercantile activities before the European colonial involvement. In this regard, Swahili urban tradition differed from other tropical Islamic cities, such as in Morocco, Mali, Egypt or the Middle East, where markets fulfilled the role of social and economic hubs and, in terms of movement, major transitory/meeting spaces in the trading towns. Yet, the Swahili urban tradition thrived for centuries as a well-connected cosmopolitan type of tropical urbanism. As research has suggested, the public role of spaces associated with trade might have been fulfilled by houses. Using approaches of space syntax and network analysis, this article studies the morphology of the houses considering whether it could have been the courtyards that simulated the role of markets thanks to their transitory spatial configuration. The results are discussed reflecting on other models of houses with courtyards, especially the modern Swahili house appearing later in the colonial era when markets began to be established, and Islamic houses known from elsewhere.

Buried solutions: How Maya urban life substantiates soil connectivity

Soils are a pivot of sustainable development. Yet, urban planning decisions persist in compromising the usability of the urban soils resource. Urban land cover expansion to accommodate an increasing population results in soil sealing. Concealment of and physical obstructions to soils prevent urban populations from engaging with their soil dependency. The concept of soil connectivity recognises that nurturing mutually beneficial soil–society relations is an essential dimension for achieving soil security. The concentrated populations of urban environments acutely require productive soil–society relations and offer the greatest potential for enhancing soil connectivity. Soil connectivity remains notably under-researched, however, resulting in deficient evidence to substantiate exactly how soil connectivity can contribute to sustaining urban life. The entanglement of soil and urban development has been critical throughout history, but seldom recognised in soil security discourse. We review the manifestation of effective soil connectivity in Precolumbian lowland Maya tropical urbanism. Archaeological evidence reveals, first, that lowland Maya urban settlement patterns largely preserved the availability, proximity, and accessibility of soils in the subdivision and configuration of urban open space. Second, Maya urban life included practices that proactively contributed to the formation of soils by adding to the stock of soils and improving beneficial soil properties of the thin and often nutrient-poor soils resulting from the regionally dominant karstic lithology. Third, a range of Maya landscape modifications and engineering practices enabled the preservation and protection of soils within urban environments. We derive evidence-based insights on an urban tradition that endured for well over two millennia by incorporating intensive soil–society relationships to substantiate the concept of soil connectivity. Inspiring urban planning to stimulate soil connectivity through enhancing the engagement with soils in urban life would promote soil security.

Towards a Tropical Urbanism for Cairns, Australia

This paper engages with debates about tropical cities and climate responsive design to consider the emergence of two local government master plans and one planning scheme provision explicitly addressing the tropical climate in Cairns, Australia. The undergirding concept of these initiatives is a terminology of Tropical Urbanism, a simultaneously environmental and social/cultural term that captures issues such as climate, lifestyle and identity in the constitution of the urban fabric. Through a detailed reading of the documents, combined with interviews with local architects and planners, this paper positions Tropical Urbanism as an environmentally aware version of New Urbanism and as a distinctive language of urban design emerging in the regional context of tropical Australia. Place-based initiatives such as these are important to improving the design outcomes and sustainability of regional cities, and we suggest Tropical Urbanism could be further reinforced by the social/cultural and political nuances of a more progressive Critical Regionalist approach.

Sustainable Tropical Urbanism: Insights from Cities of the Monsoonal Asia-Pacific

The Tropics is experiencing the fastest growing urbanisation on the planet and faces serious sustainability issues. This introduction to the eTropic Special Issue on ‘Sustainable Tropical Urbanism’ calls for a notion of plural sustainabilities in order to critique how urban sustainability has mainly been developed in temperate zones and transferred to tropical regions; but also, to recognise shared aspects of the Tropics, including climate change and environmental challenges, as well as histories of colonialism and their continuing postcolonial cultural and socioeconomic effects on peoples of the Tropics and their futures. These threads are drawn together under a conceptual trio of Place, Past, and People in order to further explore these similarities and differences. Narrowing the focus to the monsoonal Asia-Pacific region, this Special Issue presents case studies from Khulna and Chittagong in Bangladesh; Singapore and the Indonesian city of Semarang in Southeast Asia; and the regional city of Cairns in tropical northeast Australia. This Special Issue of eTropic brings together research articles, scoping reviews and viewpoints from multiple disciplines and interdisciplines to explore the dynamics of sustainable tropical urbanism.

Anicteric Leptospirosis-Associated Meningitis in a Tropical Urban Environment, Brazil.

While studying aseptic meningitis in Salvador, Brazil, we diagnosed anicteric leptospirosis in 1.7% (5/295) of patients hospitalized for aseptic meningitis. Leptospirosis-associated meningitis patients had lower mean cerebrospinal fluid cell counts and protein than other-cause aseptic meningitis (p<0.05). Clinicians must consider leptospirosis-associated meningitis in appropriate clinical-epidemiologic contexts.

Light Absorbing Properties of Primary and Secondary Brown Carbon in a Tropical Urban Environment.

Brown carbon (BrC) has significant climatic impact, but its emission sources and formation processes remain under-represented in climate models. However, there are only limited field studies to quantify the light absorption properties of specific types of primary and secondary organic aerosols (POAs and SOAs) in different environments. This work investigates the light absorption properties of the major OA components in Singapore, a well-developed city in the tropical region, where air quality can be influenced by multiple local urban sources and regional biomass burning events. The source-specific mass absorption cross-section (MAC) and wavelength dependence of different BrC components were quantified based on highly time-resolved aerosol chemical composition and absorption measurements. In particular, the combustion-related emission sources were the primary contributors to BrC light absorption and they were moderately absorbing. The SOA materials, which were freshly formed under atmospheric conditions with industrial influences, were also moderately light absorptive. The aged SOA components that were composed of aged regional emissions, including biomass burning and coal combustion emissions from nearby regions, were weakly light absorbing, highlighting the possibility of photobleaching of BrC during their atmospheric aging and dispersion. Lastly, our estimations illustrate that typical urban POAs and SOAs can contribute up to approximately 36-58% of the BrC absorption, even in some urban locations that are influenced by biomass burning emissions.

Influence of Rainfall on Leptospira Infection and Disease in a Tropical Urban Setting, Brazil.

The incidence of hospitalized leptospirosis patients was positively associated with increased precipitation in Salvador, Brazil. However, Leptospira infection risk among a cohort of city residents was inversely associated with rainfall. These findings indicate that, although heavy rainfall may increase severe illness, Leptospira exposures can occur year-round.

Assessing the response of odonates (dragonflies and damselflies) to a tropical urbanization gradient

Abstract Understanding species responses to urbanization is important to realize their specific conservation needs. Odonates (dragonflies and damselflies) are freshwater insects perceived as good ecological indicators. To investigate responses of tropical odonates to an urbanization gradient, we sampled adult odonates along an urbanization gradient at six sites along the Mula River across Pune City, Maharashtra, India. For species–habitat analysis, we first performed a variable reduction using principal component analysis. we analyzed species–habitat data using redundancy analysis and canonical correspondence analysis. We documented 15 odonates across 6 sites. Our statistical analyses on patterns of odonate assemblages across sites and environmental variables did not return significant results. However, we detected site-exclusivity in a few species based on occurrence data and identified urban sensitive, urban tolerant and generalist species. We found that the odonate diversity was highest at a moderately urbanized site. We believe that increase in diversity due to moderate amounts of disturbance can be explained by the intermediate disturbance hypothesis. Based on our data, we suggest that for the conservation of odonates in the urban context, anthropogenic disturbance needs to be regulated. Here, we demonstrate that understanding species–habitat associations is the first step towards understanding their ecological and conservation requirements. To conserve odonates and rivers in metropolitan cities like Pune, restoring original river-side habitat and reducing the disturbance at highly urbanized sites to at least intermediate levels needs to be done on an urgent basis.

Bryophyte Communities along a Tropical Urban River Respond to Heavy Metal and Arsenic Pollution

Aquatic and rheophilous bryophytes can indicate water pollution as they bioaccumulate toxic water elements. We evaluated (1) bioaccumulation of eight heavy metals and arsenic by Marchantia polymorpha L., and (2) changes in bryophyte community structure, as responses to urban pollution in southern Ecuador. To this end, we registered presence/absence and coverage of submerged bryophytes in 120 quadrats across three zones of the Zamora river inside Loja city, and a control zone in a nearby forest. We found that the concentrations of five (Al, Cd, Cu, Fe, and Zn) of the eight chemical elements and arsenic were highest in urban M. polymorpha. Moreover, bryophyte species richness decreased in urban zones. Bryophyte community structure also differed between control and city zones, but no differences were found among city zones. The control zone was composed by a more distinct set of bryophyte species, e.g., an indicator species analysis showed that 16 species had high and significant indicator values for control zone, but only 11 species were indicators of at least one of the three urban zones. We concluded that bryophytes, in general, and M. polymorpha, in particular, can be suitable biomonitors of water quality in tropical urban rivers.

Effect of Rainfall on the Microbial Water Quality of a Tropical Urban Catchment.

Wet weather conditions have been associated with increased bacterial and viral counts in surface waters. Moreover, heavy rainfall and flooding were found to be the most common events preceding waterborne disease outbreaks associated with extreme weather conditions. This study aimed to examine the effect of rainfall on the quality of surface waters and to determine its suitability for primary contact recreation during wet weather conditions. A total of 228 catchment water samples were collected during wet and dry periods. Parameters that were found to increase with increasing rainfall were , enterococci, somatic coliphages, and turbidity, whereas total dissolved solids were found to decrease. Positive correlations ( < 0.05) were observed between cumulative rainfall and geometric mean concentrations of , enterococci, somatic coliphages, and turbidity ( = 0.69-0.95), whereas a negative correlation was observed between cumulative rainfall and total dissolved solids ( = -0.58). In addition, a rapid decline in water quality was observed during heavy rainfall that resulted in failure to meet recreational water quality guidelines. In view of public health and safety, primary recreational activities in the water catchment may not be advisable during or immediately after a rainfall event due to poor water quality.