•A thin green roof with 40-mm substrate can provide satisfactory peak mitigation.•Peak mitigation can still occur after depletion of retention capacity.•Peak mitigation potential can recover ...relatively quickly.•For long heavy rainfalls, detention may be more important than retention.
Urbanization replaces permeable surfaces with relatively impervious ones to intensify mass and temporal response of stormwater runoff. Under heavy rainfalls, urban runoff could impose tremendous stress on the drainage systems, contributing to combined sewer overflow and flooding. Green roof offers an on-site source-reduction sustainable stormwater management measure that mimics pre-development hydrologic functions. It can retain and detain stormwater as well as delay and suppress peak discharge. However, previous studies were conducted mainly outside the tropics. Since green-roof hydrologic performance can be notably influenced by local meteorological conditions, dedicated investigation in the tropics are necessary. Moreover, substrate depth has long been regarded as an influential factor in green-roof stormwater retention, but recent findings have implicated that such relationship may be more complex. This study (1) evaluates green roof stormwater mitigation performance and potentials in humid-subtropical Hong Kong; and (2) investigates systematically the effect of substrate depth and addition of rockwool, a high water-retention growth medium, on quantitative performance. Using multiple 1.1-m2 raised green-roof platforms placed on an urban rooftop, the effect of four substrate-depth treatments on stormwater mitigation performance was examined over a 10-month study period. The results show that, while the retention under Hong Kong's frequent and heavy rainfall regime seems to be less effective, remarkable peak reduction and peak delay were evidently expressed even when the green-roof systems have reached full moisture-storage capacity. No statistical significance was found between treatments, despite the slightly higher mean performance of the 80-mm soil substrate. Satisfactory peak performance of the 40-mm soil substrate implies that a thin substrate can provide effective peak mitigation, especially if building loads are of concern. Extensive green roof remains as a promising alternative mitigation strategy to urban stormwater management in Hong Kong with potential application to other tropical areas.
Green roof, an increasingly common constituent of urban green infrastructure, can provide multiple ecosystem services and mitigate climate-change and urban-heat-island challenges. Its adoption has ...been beset by a longstanding preconception of attracting urban pests like mosquitoes. As more cities may become vulnerable to emerging and re-emerging mosquito-borne infectious diseases, the knowledge gap needs to be filled. This study gauges the habitat preference of vector mosquitoes for extensive green roofs vis-à-vis positive and negative control sites in an urban setting. Seven sites in a university campus were selected to represent three experimental treatments: green roofs (GR), ground-level blue-green spaces as positive controls (PC), and bare roofs as negative controls (NC). Mosquito-trapping devices were deployed for a year from March 2015 to 2016. Human-biting mosquito species known to transmit infectious diseases in the region were identified and recorded as target species. Generalized linear models evaluated the effects of site type, season, and weather on vector-mosquito abundance. Our model revealed site type as a significant predictor of vector mosquito abundance, with considerably more vector mosquitoes captured in PC than in GR and NC. Vector abundance was higher in NC than in GR, attributed to the occasional presence of water pools in depressions of roofing membrane after rainfall. Our data also demonstrated seasonal differences in abundance. Weather variables were evaluated to assess human-vector contact risks under different weather conditions. Culex quinquefasciatus, a competent vector of diseases including lymphatic filariasis and West Nile fever, could be the most adaptable species. Our analysis demonstrates that green roofs are not particularly preferred by local vector mosquitoes compared to bare roofs and other urban spaces in a humid subtropical setting. The findings call for a better understanding of vector ecology in diverse urban landscapes to improve disease control efficacy amidst surging urbanization and changing climate.
Display omitted
•Mosquito-abundance data on green roofs and control sites were monitored for a year.•A majority of the captured vector mosquitoes belonged to global invasive species.•Our model revealed significantly lower vector abundance on the studied green roofs.•Site type, season and weather were significant predictors of vector abundance.•Findings could gauge disease transmission risk and inform urban greening policies.
Urbanization engenders habitats with distinctive and often adverse microclimates. Green spaces are actively incorporated in urban designs to make cities resilient against climate-change, disease ...spread and other environmental challenges. Adoption of green roof as an innovative urban green infrastructure has been hindered by the perceived disservice of attracting urban pests like mosquitoes. This study evaluated important microclimatic attributes that explain vector abundance differences between urban extensive green roofs and two control site types in humid-subtropical Hong Kong. Mosquito-trapping data were collected fortnightly for a year (March 2015 to 2016) from seven sites representing three experimental treatment groups: green roofs (GR), low-elevation blue-green spaces as positive controls (PC), and bare roofs as negative controls (NC). Concurrent ambient microclimate parameters were measured on site. Human-biting female mosquitoes of species known to transmit infectious diseases locally and globally constituted the vector abundance data. Generalized linear models evaluated the effects of site-specific microclimatic factors on abundance. Time-lagged microclimatic measurements were analyzed to reveal latent effects. The models consistently identified temperature and wind speed as significant factors. Wind speed accounted for differences in abundance across site types, while temperature exerted its effect on abundance chiefly through seasonal variation. Contrary to common preconception, urban green roofs had significantly lower vector abundance relative to controls. High wind exposure on elevated buildings, which acted as a deterrent of mosquito flight, was found to be the underlying microclimatic factor. Our findings could inform urban greening design and policy, as well as disease control and transmission risk assessment.
•The studied green roofs had significantly lower vector abundance than controls.•Temperature and wind speed were statistically significant microclimatic factors.•Strong winds on elevated urban rooftops present adverse conditions for mosquitoes.•Temperature affects vector abundance mainly through seasonal variations.•Findings call for a better understanding of urban microclimate and vector ecology.
Increasing visits to protected areas in China have drawn public attention on the negative impacts on ecologically sensitive areas. Understanding potential determinants of the environmentally ...responsible behavioral intention of nature-based tourists has become a common focus in tourism studies. Scholars seek to explore potential determinants of visitors’ behavior, and the findings can be referenced by the managers of protected areas to formulate visitor management strategies. On the basis of a sample of 402 questionnaires collected in protected areas in South China, namely, Nanling National Forest Park and Dinghu Mountain National Nature Reserve, we explore the association between visitors’ place attachment and their satisfaction and environmentally responsible behavioral intention. The results show that place dependence and place identity are positively correlated with the satisfaction and environmentally responsible behavioral intention of visitors; thus, our results differ from those of previous studies on Western visitors. The lack of significant results regarding place social bonding revealed the shortcomings associated with visitor management in China’s protected areas. Chinese culture has a great influence on various findings in this study. All of the findings provide significant insights for management and policy-making regarding protected areas worldwide to accommodate the rising number of nature-based visitors to China.
Context
Urban green space (UGS) is widely espoused in sustainable urban design. Notwithstanding its ecosystem services, UGS is commonly perceived as inadvertent habitats for urban mosquitoes. ...Moreover, the lack of ecological understanding of mosquitoes and their urban habitats renders vector control in green spaces without reliance on chemical and bio-pesticides especially challenging.
Objectives
This study envisages the application of a comparative analytical method for the evaluation and optimization of vector management in different urban spaces. The research examines the extent of male habitat preference as measured by population characteristics of urban adult mosquitoes on green roof and control sites.
Methods
Adult mosquito traps were deployed on green roofs (GR), bare roofs (negative control, NC), and low-elevation gardens (positive control, PC). Distribution of male and female members of vector species were analyzed
Results
Urban adult male mosquitoes exhibited highly-selective habitat use of the studied urban spaces, in that they were clustered chiefly in PC. Their spatial distributions are consistently explained by site group even under the stringent measure of presence/absence. The sex ratios of GR and NC were highly skewed toward females, which lends further to the interpretation of strong male habitat preference for the studied PC gardens.
Conclusions
Urban mosquitoes do not display similar degrees of affinity for different types of green infrastructure. The methodology used can help prioritize urban sites and optimize control strategies. The uses of amenable environmental features salient to mosquito survival in landscape design should be explored as a sustainable and environmentally-friendly vector management approach.
Climate change and urbanisation have exacerbated social inequities. Increasing urban heat has made high-density housing units a vulnerability hotspot. Alternatives to extended air-conditioning are ...required. This research sought evidence on using urban parks as a sustainable alternative by low-income households deprived of adequate living space. We interviewed occupants of tiny flats (approx. 10 m2), known as subdivided units, and compared their park visiting routines and thermal comfort practices with other urban dwellers in Hong Kong. The substandard conditions of these small units have contributed to dwellers' sensitivity and lower capacity to adapt to summer heat, resulting in heat-related illness. The space-poor households have taken a wider range of adaptive actions and visited urban parks more frequently for cooling. Their higher mobility between home and nearby parks has shortened their home-stay time that would otherwise demand residential space cooling. The findings are important for reconsidering and redressing the uneven distribution of urban green spaces. Poor housing conditions and heat stress have forced disadvantaged households to seek refuge from natural cool spaces, such as vegetated and shaded areas of urban parks. Measures for increasing their accessibility, availability and capacity for heat mitigation are conducive to pro-poor and pro-climate spatial planning.
•We examine the vulnerability to urban heat of households who live in tiny flats.•They are economically disadvantaged and have experienced greater heat stress.•They more frequently use urban parks as a cool public space to mitigate heat stress.•Those who often visit parks for cooling use air-conditioner for shorter hours.•Park improvements in high-density tropical cities can be pro-poor and pro-climate.
•Antecedent condition and duration play an auxiliary role in green-roof retention.•Solar radiation and wind speed contributed significantly to retention.•Urban roofs may experience wider temperature ...extremes than ground conditions.•Higher maximum temperatures enhance evapotranspiration and subsequent retention.•Key factors could inform site choice and green-roof design to maximize benefits.
Green roofs have received considerable attention for multiple ecosystem services which include stormwater amelioration. Offering sustainable stormwater source-control, green roofs utilize otherwise unused impervious urban surfaces to restore pre-development hydrologic functions such as infiltration and retention. Its ability to retain stormwater is related to external and internal factors. Meteorological conditions prior to a rainfall event can influence antecedent evapotranspiration, the only water-exit pathway of the green-roof system besides discharge. Whereas evapotranspiration may be difficult and costly to measure directly, other common meteorological conditions can be monitored conveniently and inexpensively even prior to actual green-roof installation. Identifying salient on-site meteorological factors may provide valuable insights into hydrologic dynamics, and inform green-roof design and planning decisions. A statistical regression approach identified potential antecedent meteorological factors and moisture indicators of extensive green-roof retention. Continuous field-monitoring data revealed the combined effects of rainfall depth, wind speed, solar radiation, and antecedent dry weather period to explain the measured stormwater retention under a humid subtropical rainfall regime. Amongst the studied environmental factors, solar radiation and wind speed contributed notably to green-roof stormwater retention and may provide a dependable basis to assist green-roof site selection when resources are limited. It is important to incorporate site-specific planning and assessment prior to green infrastructure design and implementation to maximize hydrologic and evaporative cooling services in cities with complex topographical features.
Urban green spaces provide multiple benefits but incur some negative impacts. We employed the contingent valuation method to investigate Hong Kong residents’ willingness‐to‐pay to improve urban green ...space provision. A questionnaire collected 316 responses from urban‐park visitors. It assessed perceptions of positive benefits and negative impacts and influences on willingness‐to‐pay. Health benefits attracted top scores, followed by environment and ecology. For negative impacts, road safety ranked first, followed by risks and hazards, and health and sanitation concerns. More educated and younger respondents were more willing to pay. One third of respondents, mainly the less educated and older people, registered protest votes for diverse reasons. Logistic regression was used to analyse the probability of positive bids with a socio‐demographic model and an extended model incorporating explanatory perception variables. Ordinal regression identified willingness‐to‐pay determinants. Both statistical tests found perceived environmental and ecological benefits as key willingness‐to‐pay predictors. The perceived negative impacts of health and sanitation concerns were correlated with willingness‐to‐pay, indicating a desire to improve and contradicting past studies and expectations. The results highlighted the importance of exploring willingness‐to‐pay from a rarely studied perspective of valuating the potential improved utility of urban green space through suppressing negative impacts. The findings can inform park and urban management to meet user expectations.
We investigated willingness to pay (WTP) to improve urban green space in Hong Kong. We incorporated perceived benefits and negative impacts as predictors of WTP. Perceived environmental and ecological benefits were crucial determinants of WTP. Health and sanitation concerns indicate a significant association with WTP.
Climate change has induced increasingly alarming impacts on urban environment. Adaptation is one of the most common measures to mitigate the impacts and reduce vulnerability. This study explored the ...individual adaptation from a cognitive and psychological perspective that has rarely been adopted. The current study aims to measure the risk perception (RP) and perceived adaptive capacity (PAC) of individuals and explore the relationships of the two factors with the attitude and behavior on sustainable adaptation. Some 483 successful questionnaire samples were collected through telephone surveys in Hong Kong. Our major findings include: (1) the inconsistent results from regression analysis of PAC as a single construct and results from factors of PAC obtained from exploratory factor analysis; (2) higher level of PAC in terms of “Mental flexibility, knowledge and interest in global warming” promotes sustainable attitude on adaptation and frequency of use of electrical fan; (3) sustainable attitude of individuals is weaker when they perceive a high effectiveness in their adaptive action and availability of resource; and (4) individuals demonstrating higher level of risk perception uses air-conditioners more frequently. The results showed that some individuals might express maladaptations which may potentially lead to a deterioration of overall public adaptation and long-term sustainability in the society. Such an aberrant response would imply a need for education on concepts of risk and sustainability on climate change adaptation to rectify the misconception.
•Questionnaire survey and statistical analysis evaluated perception of climate change.•Two factors of perceived adaptive capacity (PAC) of residents were identified.•Risk perception and PAC were positively correlated with attitude.•High risk perception tends to engage in more unsustainable adaptive behavior.•Educating people on sustainable adaptive attitude and behavior are essential.
Urban green space (UGS) offers users multiple ecosystem services and amenities. This study investigated whether residents used UGS visitation in summer as a sustainable measure to tackle hot weather ...and associated climate-change impacts in humid-subtropical Hong Kong. Attributes of the indoor residential environment, seldom examined in park-visitation studies, were evaluated as push factors to visit UGS through a push–pull theoretical framework. A questionnaire survey of 483 respondents targeted urban park users. The results indicated that UGS visit frequency and stay duration were relatively low in hot summer. Ordinal multiple regression showed that indoor living conditions, residence location, living routine, and habit and personal health impacts were significantly correlated with UGS visits. Interdependence between push and pull factors was detected, demonstrating that intrinsic UGS environmental conditions could constrain UGS visits despite the motivations of push factors. The results indicated the need to improve the microclimate-regulating function in UGS. It could be achieved mainly by optimizing the nature-based design to promote UGS as an adaptive measure to combat the thermal stress brought by climate change. The findings yielded hints to shape visiting habits and suggestions to improve UGS management.
PDF
