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Nature-based solution enhances resilience to flooding and catalyzes multi-benefits in coastal cities in the Global South
Abstract
Coastal cities are facing a rise in groundwater levels induced by sea level rise, further triggering saturation excess flooding where groundwater levels reach the topographic surface or reduce the storage capacity of the soil, thus stressing the existing infrastructure. Lowering groundwater levels is a priority for sustaining the long-term livelihood of coastal cities. In the absence of studies assessing the possibility of using tree-planting as a measure of alleviating saturation excess flooding in the context of rising groundwater levels, the multi-benefit nature of tree-planting programs as sustainable Nature-based solutions (NBSs) in coastal cities in the Global South is discussed. In environments where groundwater is shallow, trees uptake groundwater or reduce groundwater recharge, thereby contributing to lower groundwater levels and increasing the unsaturated zone thickness, further reducing the risk of saturation excess flooding. Tree-planting programs represent long-term solutions sustained by environmental factors that are complementary to conventional engineering solutions. The multi-benefit nature of such NBSs and the expected positive environmental, economic, and social outcomes make them particularly promising. Wide social acceptance was identified as crucial for the long-term success of any tree-planting program, as the social factor plays a major role in addressing most weaknesses and threats of the solution. In the case of Nouakchott City (Mauritania), where a rise in groundwater levels has led to permanent saturation excess flooding, a tree-planting program has the potential to lower the groundwater levels, thereby reducing flooding during the rainy season.
... NbS offer transformative strategies to enhance hydrological resilience by leveraging the inherent adaptive capacities of ecosystems (Ben Amor et al. 2024;Dubois et al. 2024;Sun et al. 2024). These approaches focus on restoring and escalating climate risks. ...
Climate change is fundamentally transforming global hydrological systems, exacerbating water scarcity, degrading water quality, and amplifying flood risks. This review critically examines the impacts of climate change on hydrological resilience, focusing on the increasing frequency and severity of extreme hydrological events such as floods and droughts, and their disproportionate effects on vulnerable regions with limited water resources. The review explores the role of nature-based solutions (NbS)—such as wetland restoration, reforestation, riparian buffer protection, and sustainable land management—as key strategies for mitigating climate-induced hydrological extremes. NbS leverage ecosystem services to reduce flood risks, improve water quality, and support groundwater recharge, offering adaptive, multi-functional approaches when combined with engineered infrastructure. In addition, the review discusses advancements in hydrological modeling, including the use of process-based models, machine learning algorithms, and scenario-based approaches, highlighting their potential for improving predictions of hydrological system responses to climate perturbations. Despite these advancements, significant gaps remain in understanding the interactions between cascading climate-induced extremes—particularly drought-to-flood transitions—and in addressing the challenges posed by limited data in transboundary water systems. This review underscores the importance of integrating ecological and infrastructural approaches in water resource management. It identifies emerging methodologies, such as real-time data assimilation and Bayesian frameworks, as crucial for enhancing the precision of hydrological predictions and informing effective decision-making. By synthesizing the latest research, this paper offers a comprehensive framework for addressing the challenges of climate-induced water crises and advancing hydrological resilience.
... Coastal cities are also economic hubs for trade and tourism, leading to intensive land use and potential environmental conflicts. Effective management in coastal cities necessitates balancing development with environmental protection and disaster preparedness [25,26]. However, relatively few studies have been conducted to assess and simulate the ecological environment quality in coastal cities. ...
In the face of persistent global environmental challenges, evaluating ecological environment quality and understanding its driving forces are crucial for maintaining the ecological balance and achieving sustainable development. Based on a case study of Changle District in Fuzhou, China, this research employed the Remote Sensing Ecological Index (RSEI) method to comprehensively assess ecological environment quality and analyze the impact of various driving factors from 2000 to 2020. Based on the GeoSOS-FLUS model, this study simulated and predicted land use classifications if maintaining the RSEI factors. The results reveal an overall improvement in the southern and southwestern regions, while the northwest and eastern areas face localized degradation. The RSEI index increased from 0.6333 in 2000 to 0.6625 in 2022, indicating significant ecological shifts over the years. The key driving factors identified include vegetation coverage, leaf area index, and aerosol levels. Industrial emissions and transportation activities notably affect air quality, while land use changes, particularly the expansion of construction land, play a critical role in altering ecological conditions. If maintaining the current RESI factors without any improvement, Changle District will experience continued urbanization and development, leading to an increase in built-up areas to 32.93% by 2030 at the expense of grasslands. This study offers valuable insights for policymakers and environmental managers to formulate targeted strategies aimed at reducing industrial and traffic emissions, optimizing land use planning, and enhancing ecological sustainability. The methodology and findings provide a robust framework for similar assessments in other rapidly urbanizing regions, contributing to the broader discourse on sustainable land use and ecological conservation. By advancing the understanding of ecological environment quality and its driving forces, this research supports the development of informed environmental protection and sustainable development strategies for coastal regions in developing countries globally.
Climate change has become a global issue and affects various regions at different levels. The hydro-climatic conditions and the natural fragility of Sub-Saharan Africa (SSA) make it prone to floods. The review was intended to comprehensively explore the determinants of floods in the continent and their effects on public health. An extensive systematic literature search in English was conducted for peer-reviewed papers, abstracts and internet articles, grey literature, and official Government documents and analysed to identify common themes, findings, and outcomes. Finally, the findings were categorized into common themes.
The review revealed that the frequency and intensity of precipitations have increased in recent decades in SSA. This is worsened by anthropogenic activities including urban sprawl, population growth, and land use changes. The health effects of floods are diverse, varied, and specific to a particular context which can be immediate and long-term. The economic losses due to the flood events in the continent are huge.
In conclusion, Governments across the continent need to give flood management a top priority as part of national disaster preparedness, response, and mitigation. Floods cannot be managed in isolation; it has to be incorporated into national urban planning with urbanization to make cities resilient and sustainable.
In Africa, vector-borne diseases are a major public health issue, especially in cities. Urban greening is increasingly considered to promote inhabitants’ well-being. However, the impact of urban green spaces on vector risk remains poorly investigated, particularly urban forests in poor hygienic conditions. Therefore, using larval sampling and human landing catches, this study investigated the mosquito diversity and the vector risk in a forest patch and its inhabited surroundings in Libreville, Gabon, central Africa. Among the 104 water containers explored, 94 (90.4%) were artificial (gutters, used tires, plastic bottles) and 10 (9.6%) were natural (puddles, streams, tree holes). In total, 770 mosquitoes belonging to 14 species were collected from such water containers (73.1% outside the forested area). The mosquito community was dominated by Aedes albopictus (33.5%), Culex quinquefasciatus (30.4%), and Lutzia tigripes (16.5%). Although mosquito diversity was almost double outside compared to inside the forest (Shannon diversity index: 1.3 vs. 0.7, respectively), the species relative abundance (Morisita–Horn index = 0.7) was similar. Ae. albopictus (86.1%) was the most aggressive species, putting people at risk of Aedes-borne viruses. This study highlights the importance of waste pollution in urban forested ecosystems as a potential driver of mosquito-borne diseases.
Nature-based solutions (NbS) have gained traction in Southeast Asia and the Pacific region over the last decade. While the benefits of NbS are established for most urban contexts, more research is necessary to examine the potential of these solutions in the Global South, particularly in historically disadvantaged contexts such as informal settlements. Responding to this gap, we analyse both grey and academic sources to examine past NbS projects in informal settlements in Southeast Asian and Pacific countries. We identified six main types of NbS that are used to address various social, ecological, and cultural challenges in informal settlements. Some NbS are different from those described in the Global North, ranging from the use of traditional community gardens to enhance food security to the implementation of constructed wetlands as wastewater treatment systems. NbS in the region are often framed as grassroots initiatives spearheaded by local communities or as technical systems implemented within “upgrading programs” delivered by multilateral banks, researchers or international organisations. Analysing the motivations behind these projects, we provide insights into which systems have been used in response to specific needs such as efforts to promote climate adaptation, support food security or compensate residents for disruptions. We outline important social and political implications of the implementation of NbS still understudied in the literature, such as the framing of NbS as “placeholders” for future development or as “compensation” for the disruptions caused by resettlement projects.
Funding and financing challenges remain a persistent barrier to implementing nature‐based solutions that enhance ecosystem services, facilitate adaptation to climate change, and combat environmental stressors in cities. In the absence of adequate public financial resources, private funds are often expected to fill the gap. But market‐driven, nature‐based solutions can contribute to an inequitable distribution of urban ecosystem services by focusing on net benefits provided by nature. To help foster sustainable development and ensure that nature‐based solutions reach diverse and historically marginalized populations and communities, this scoping review explores the ecosystem services provided by nature‐based solutions and the payment mechanisms that produce and maintain them, focusing on literature on the United States. Findings suggest that the net benefits provided by nature‐based solutions and the available payment mechanisms vary based on the solution utilized (e.g., urban trees, parks, community gardens). Further, the distribution of benefits from nature‐based solutions is influenced by local historical, cultural, political, economic, and environmental contexts, the voices included in decision‐making, and the payment mechanisms used. Inspired by social equity principles, we present a framework for ecosystem service provision that is sensitive to market‐driven funding, financing, and partnerships. Practitioners can use this framework to assess whether payment schemes work in tandem with place (the local context) and process (governance and planning approaches) to ameliorate or exacerbate disparities in nature‐based solutions and the benefits they provide to people.
Background
Plasmodium vivax malaria is one of the major infectious diseases of public health concern in Nouakchott, the capital city of Mauritania and the biggest urban setting in the Sahara. The assessment of the current trends in malaria epidemiology is primordial in understanding the dynamics of its transmission and developing an effective control strategy.
Methods
A 6 year (2015–2020) prospective study was carried out in Nouakchott. Febrile outpatients with a clinical suspicion of malaria presenting spontaneously at Teyarett Health Centre or the paediatric department of Mother and Children Hospital Centre were screened for malaria using a rapid diagnostic test, microscopic examination of Giemsa-stained blood films, and nested polymerase chain reaction. Data were analysed using Microsoft Excel and GraphPad Prism and InStat software.
Results
Of 1760 febrile patients included in this study, 274 (15.5%) were malaria-positive by rapid diagnostic test, 256 (14.5%) were malaria-positive by microscopy, and 291 (16.5%) were malaria-positive by PCR. Plasmodium vivax accounted for 216 of 291 (74.2%) PCR-positive patients; 47 (16.1%) and 28 (9.6%) had P. falciparum monoinfection or P. vivax – P. falciparum mixed infection, respectively. During the study period, the annual prevalence of malaria declined from 29.2% in 2015 to 13.2% in 2019 and 2.1% in 2020 ( P < 0.05). Malaria transmission was essentially seasonal, with a peak occurring soon after the rainy season (October–November), and P. vivax infections, but not P. falciparum infections, occurred at low levels during the rest of the year. The most affected subset of patient population was adult male white and black Moors. The decline in malaria prevalence was correlated with decreasing annual rainfall (r = 0.85; P = 0.03) and was also associated with better management of the potable water supply system. A large majority of included patients did not possess or did not use bed nets.
Conclusions
Control interventions based on prevention, diagnosis, and treatment should be reinforced in Nouakchott, and P. vivax -specific control measures, including chloroquine and 8-aminoquinolines (primaquine, tafenoquine) for treatment, should be considered to further improve the efficacy of interventions and aim for malaria elimination.
Recent studies have focused on the effect of large tropical cyclones (hurricanes) on the shore, neglecting the role of less intense but more frequent events. Here we analyze the effect of the offshore tropical storm Melissa on groundwater data collected along the North America Atlantic coast. Our meta‐analysis indicates that both groundwater level and specific conductivity significantly increased during Melissa, respectively reaching maximum values of 1.09 m and 25.2 mS/cm above pre‐storm levels. Time to recover to pre‐storm levels was 10 times greater for groundwater specific conductivity, with a median value of 20 days, while groundwater level had a median recovery time of 2 days. A frequency‐magnitude analysis indicates that the percent of time with salinization is higher for Melissa than for energetic hurricanes. Given the high frequency of these events (return period of 1–2 years), and the long time needed for groundwater conditions to return to normal levels, we conclude that increasingly frequent moderate storms will have a significant impact on the ecology of vegetated shorelines.
Evaporative loss of interception (Ei) is the first process occurring during rainfall, yet its role in large-scale surface water balance has been largely underexplored. Here we show that Ei can be inferred from flux tower evapotranspiration measurements using physics-informed hybrid machine learning models built under wet versus dry conditions. Forced by satellite and reanalysis data, this framework provides an observationally constrained estimate of Ei, which is on average 84.1 ± 1.8 mm per year and accounts for 8.6 ± 0.2% of total rainfall globally during 2000–2020. Rainfall frequency regulates long-term average Ei changes, and rainfall intensity, rather than vegetation attributes, determines the fraction of Ei in gross precipitation (Ei/P). Rain events have become less frequent and more intense since 2000, driving a global decline in Ei (and Ei/P) by 4.9% (6.7%). This suggests that ongoing rainfall changes favor a partitioning towards more soil moisture and runoff, benefiting ecosystem functions but simultaneously increasing flood risks. Canopy rainfall interception (Ei) is a key component of global water cycle. Here, the authors quantify Ei using flux tower data and machine learning, and find that rainfall gets less partitioned into Ei as it gets more intense and less frequent.
The paper discusses the persistence of floods focusing attention on the city of Dar es Salaam (DSM), where over 10% of the Tanzanian population resides. Beyond the metaphor of exploding population growth, the city has witnessed recurring floods. Whilst studies abound on the vulnerability and socioeconomic losses associated with flood hazards, limited studies exist about the persistence of flood hazards in DSM. This study attempts to analyse (i) the various factors that exacerbate flooding in Dar es Salaam; and (ii) the extent of interdependency and interconnection of the various factors. A thorough systematic desk review of the literature was conducted focusing on Dar es Salaam. The literature surveyed shows how colonial planning legacy has (in)directly shaped the geomorphology of DSM, and instigated the persistence of present-day floods. Specifically, rapid spatial urbanization in informality, weak capacity in spatial development control, limited coverage of drainage infrastructure, geomorphology, climate change and variability, and low coverage of solid waste collection were discovered as the major factors exacerbating floods in DSM. Besides the interdependency and interconnected nature of these factors, the review showed how the persistence of flood hazards in Dar es Salaam is influenced by the coexistence and synergistic forces of the aforementioned: rapid spatial urbanization with informality, weak capacity in spatial development control, limited coverage of drainage infrastructure, geomorphology, climate change and variability and low coverage of solid waste collection. The study recommends that urban planners pay attention to city-specific context and the interlinked nature of the factors exacerbating floods in tailoring interventions.
The recognition of nature-based solutions (NbS) is on a growing trend worldwide in an era of climate change, and intensified demand for improved human health, better preparedness for disasters, food and water security. The solutions seek to restore, protect and sustainably manage natural and modified ecosystems to optimize biodiversity and human wellbeing benefits. In this study, a scientometric analysis of works indexed in Web of Science database until April 2022 was carried out to analyze 123 studies on NbS in Africa. The most active institutions, authors, and countries involved in publication on the topic and their evolution with time was assayed. African countries with exception of South Africa conducted limited research on the topic. About 38.2% of total searched outputs were affiliated to South African institutions. Most research output on the search query was in the environmental sciences and ecology subjects. A sluggish growth in research on the topic was established from the bibliographic coupling of authors and countries as well as keyword analysis. The study recommended for institution and policy overhaul, creation of NbS awareness and better financing of related projects to enhance the documentation and research on the topic in Africa by African researchers to supplement research already conducted by developed countries.
This report assesses the current state of knowledge on the size of the contribution that nature-based solutions can make and the types of action they will involve. It discusses the importance of social and environmental safeguards, how nature-based solutions can be financed and the role of offsets. Most importantly, it considers the potential of nature-based solutions for mitigation to also contribute to climate adaptation and other pressing challenges.
Nature-based solutions (NBS) to climate change and other environmental challenges face a well-documented shortfall in financing and resource allocation. Economic evaluations of NBS that apply stated preference methods increasingly use time contributions instead of the traditionally used monetary contributions, especially in developing countries. These studies have focused on measuring the benefits of NBS and have not investigated the potential of freely provided community time contributions to reduce the financial needs of NBS. In this paper we investigate this potential through a systematic literature review and an analysis of four datasets from case studies in Ghana and Vietnam that apply similar questionnaires and discrete choice experiments with time contributions. We study a range of (de)motivating factors to contributing time to NBS and provide examples on the extent to which time contributions could reduce financial needs of NBS in developing countries. The results indicate that time contributions from households for the implementation and maintenance of NBS are motivated by social capital and coping appraisal. Time contribution schemes are therefore more likely to succeed in communities where social capital and coping appraisal are high and could be increased or maintained over time through the preservation and fostering of both these factors. The analysis also reveals that implementing time contributions would in general not lead to the exclusion of specific socio-demographic groups in society, such as lower income households. Finally, using two specific projects in Vietnam as examples, we calculate that time contributions can reduce 29% and 44% of the financial needs of NBS by covering the projects’ labour requirements. These results are of high importance to those working on NBS financing, awareness and behavior change campaigns, and practitioners that apply stated preference methods in developing countries.
Digitalisation is an increasingly important driver of urban development. The ‘New Urban Science’ is one particular approach to urban digitalisation that promises new ways of knowing and managing cities more effectively. Proponents of the New Urban Science emphasise urban data analytics and modelling as a means to develop novel insights on how cities function. However, there are multiple opportunities to broaden and deepen these practices through collaborations between the natural and social sciences as well as with public authorities, private companies, and civil society. In this article, we summarise the history and critiques of urban science and then call for a New Urban Science that embraces interdisciplinary and transdisciplinary approaches to scientific knowledge production and application. We argue that such an expanded version of the New Urban Science can be used to develop urban transformative capacity and achieve ecologically resilient, economically prosperous, and socially robust cities of the twenty-first century.
As human living environments face increasing challenges with resilience, the concept of nature-based solutions (NBS) was proposed in recent years as a way to promote sustainable living in urban environments. Urban forests and trees play important roles in urban ecosystems, while their potential as an NBS is promising. A bibliometric analysis was first conducted to explore the research pattern of NBS in urban environments. Studies of urban forest and tree-based green infrastructure in NBS research were further investigated using a systematic literature review method. The initial studies on NBS have increased since 2015 with 493 documents published from 142 sources in over 70 countries and regions. Keyword analysis showed green infrastructure had a rather high frequency of utility and received considerable attention. As for urban forests as nature-based solutions (UF-NBS) research, the most prominent study approaches used at different scales and the main benefits and typologies of urban forest studied in the articles were identified. UF-NBS research is still relatively scarce at present. Despite the role of urban forest and trees in addressing environmental challenges being well recognized, UF-NBS studies still need to be conducted in a more comprehensive context, taking social and economic aspects into account.
To ensure and maintain ecosystem service delivery in cities undergoing densification, strategic tree planting is important. The effects of tree location on ecosystem service delivery have been emphasised. However, there is no integrated overview of the different aspects of tree location, here called spatial contextual factors, that mediate urban tree ecosystem services. This paper presents the results of a systematic literature review and provides a comprehensive overview of spatial contextual factors recognised by research as relevant for ecosystem service delivery by urban trees. To support creating such an overview, we first gain insight into the current common understanding of what spatial context is conceptually and how it participates in the co-production of ecosystem services. We find that generally, spatial context is represented by both social and ecological structures and processes and that it mediates ecosystem services by four mechanisms along the ecosystem service cascade. In the next step, we identify 114 unique spatial contextual factors mediating 31 ecosystem services of urban trees. Of all factors, people, represented by physical location, socio-demographics or building functions, mediate the highest number of services, highlighting the importance of urban planning and design in mediating urban tree ecosystem services.
Spatiotemporal redistribution of incident rainfall in vegetated ecosystems results from the partitioning by plants into intercepted, stemflow, and throughfall fractions. However, variation in patterns and drivers of rainfall partitioning across global biomes remain poorly understood, which limited the ability of climate models to improve predictions of biome hydrological cycle under global climate change scenario. Here, we synthesized and analyzed the partitioning of incident rainfall into interception, stemflow, and throughfall by trees and shrubs at the global scale using 980 observations from 236 independent publications. We found that (1) globally, median levels of relative interception, stemflow, and throughfall accounted for 21.8, 3.2, and 73.0% of total incident rainfall, respectively; (2) rainfall partitioning varied among different biomes, due to variation in plant composition, canopy structure and macroclimate; (3) relative stemflow tended to be driven by plant traits, such as crown height:width ratio, basal area, and height, while relative interception and throughfall tended to be driven by plant traits as well as meteorological variables. Our global assessment of patterns and drivers of rainfall partitioning underpins the role of meteorological factors and plant traits in biome‐specific ecohydrological cycles. We suggest to include these factors in climate models to improve predictions of local hydrological cycles and associated biodiversity and function responses to changing climate conditions.
Dense impenetrable thickets of invasive trees and shrubs compete with other water users and thus disrupt ecosystem functioning and services. This study assessed water use by the evergreen Prosopis juliflora, one of the dominant invasive tree species in semi-arid and arid ecosystems in the tropical regions of Eastern Africa. The objectives of the study were to (1) analyze the seasonal water use patterns of P. juliflora in various locations in Afar Region, Ethiopia, (2) up-scale the water use from individual tree transpiration and stand evapotranspiration (ET) to the entire invaded area, and 3) estimate the monetary value of water lost due to the invasion. The sap flow rates of individual P. juliflora trees were measured using the heat ratio method while stand ET was quantified using the eddy covariance method. Transpiration by individual trees ranged from 1–36 L/day, with an average of 7 L of water per tree per day. The daily average transpiration of a Prosopis tree was about 3.4 (± 0.5) mm and the daily average ET of a dense Prosopis stand was about 3.7 (± 1.6) mm. Using a fractional cover map of P. juliflora (over an area of 1.18 million ha), water use of P. juliflora in Afar Region was estimated to be approximately 3.1–3.3 billion m ³ /yr. This volume of water would be sufficient to irrigate about 460,000 ha of cotton or 330,000 ha of sugar cane, the main crops in the area, which would generate an estimated net benefit of approximately US 470 million per growing season from cotton and sugarcane, respectively. Hence, P. juliflora invasion in the Afar Region has serious impacts on water availability and on the provision of other ecosystem services and ultimately on rural livelihoods.
Growing urbanisation is a threat to both mental health and biodiversity. Street trees are an important biodiversity component of urban greenspace, but little is known about their effects on mental health. Here, we analysed the association of street tree density and species richness with antidepressant prescribing for 9751 inhabitants of Leipzig, Germany. We examined spatial scale effects of street trees at different distances around participant’s homes, using Euclidean buffers of 100, 300, 500, and 1000 m. Employing generalised additive models, we found a lower rate of antidepressant prescriptions for people living within 100 m of higher density of street trees—although this relationship was marginally significant (p = 0.057) when confounding factors were considered. Density of street trees at further spatial distances, and species richness of street trees at any distance, were not associated with antidepressant prescriptions. However, for individuals with low socio-economic status, high density of street trees at 100 m around the home significantly reduced the probability of being prescribed antidepressants. The study suggests that unintentional daily contact to nature through street trees close to the home may reduce the risk of depression, especially for individuals in deprived groups. This has important implications for urban planning and nature-based health interventions in cities.
Key message
Our manuscript discussed salt tolerance mechanisms in trees, genes associated with salt stress tolerance, methods to improve the salt tolerance of trees, and research frontiers.
Abstract
Soil salinization is a global problem that seriously affects plant growth and development. Improving the salt tolerance of trees is an import economic and ecological aim in forestry. Recent studies have provided insight into resistance mechanisms in trees. Here, we present an overview of salt tolerance in trees and discuss mechanisms, genes associated and methods to improve the salt tolerance of trees, as well as research frontiers.
Projected sea-level rise will raise coastal water tables, resulting in groundwater hazards that threaten shallow infrastructure and coastal ecosystem resilience. Here we model a range of sea-level rise scenarios to assess the responses of water tables across the diverse topography and climates of the California coast. With 1 m of sea-level rise, areas flooded from below are predicted to expand ~50–130 m inland, and low-lying coastal communities such as those around San Francisco Bay are most at risk. Coastal topography is a controlling factor; long-term rising water tables will intercept low-elevation drainage features, allowing for groundwater discharge that damps the extent of shoaling in ~70% (68.9–82.2%) of California’s coastal water tables. Ignoring these topography-limited responses increases flooded-area forecasts by ~20% and substantially underestimates saltwater intrusion. All scenarios estimate that areas with shallow coastal water tables will shrink as they are inundated by overland flooding or are topographically limited from rising inland. Sea-level rise raises water tables, causing flooding from below and saltwater intrusion. A modelling study predicts that coastal California groundwater flooding will expand 50–130 m inland with 1 m of sea-level rise, with areal flooding extent strongly dependent on topography and drainage capacity.
Global models of tide, storm surge, and wave setup are used to obtain projections of episodic coastal flooding over the coming century. The models are extensively validated against tide gauge data and the impact of uncertainties and assumptions on projections estimated in detail. Global “hotspots” where there is projected to be a significant change in episodic flooding by the end of the century are identified and found to be mostly concentrated in north western Europe and Asia. Results show that for the case of, no coastal protection or adaptation, and a mean RCP8.5 scenario, there will be an increase of 48% of the world’s land area, 52% of the global population and 46% of global assets at risk of flooding by 2100. A total of 68% of the global coastal area flooded will be caused by tide and storm events with 32% due to projected regional sea level rise.
Aiming to explore the species-specific responses of biomass allocation and whole-tree transpiration in urban trees to pavement and drought, a field manipulation experiment grew saplings of two common greening trees, ash (Fraxinus chinensis Roxb.) and ginkgo (Ginkgo biloba L.). Pavement slightly increased leaf area and leaf biomass in ginkgo under sufficient water supply. When water deficit occurs, the height, basal diameter, and biomass in ash reduced and more biomass was allocated to roots, pavement aggravated the reduction of stem biomass in ash. Pavement slightly increased soil evaporation and total evapotranspiration, irrespective of whether the water supply was sufficient or not. However, whole-tree transpiration and stem sap flow increased under pavement when the water supply was sufficient for ginkgo but not so for ash. The down-regulation of water use generated by an insufficient water supply was aggravated and retarded by pavement for ginkgo and ash, respectively. Ash grows faster and can maintain its transpiration better under pavement and drought stress, making it the preferred tree for planting on paved land in urban areas.
Abstract Flood risk to urban communities is increasing significantly as a result of the integrated effects of climate change and socioeconomic development. The latter effect is one of the main drivers of rising flood risk has received less attention in comparison to climate change. Economic development and population growth are major causes of urban expansion in flood‐prone areas, and a comprehensive understanding of the impact of urban growth on flood risk is an essential ingredient of effective flood risk management. At the same time, planning for community resilience has become a national and worldwide imperative in recent years. Enhancements to community resilience require well‐integrated and enormous long‐term public and private investments. Accordingly, comprehensive urban growth plans should take rising flood risk into account to ensure future resilient communities through careful collaboration between engineers, geologists, socialists, economists, and urban planners within the framework of life‐cycle analysis. This paper highlights the importance of including urban growth in accurate future flood risk assessment and how planning for future urbanization should include measurement science‐based strategies in developing policies to achieve more resilient communities.
The conventional urban stormwater management practices focus on carrying away runoff quickly by lined conveyors, which increase the surface runoff and reduce the time of concentration, subsequently causing floods in downstream areas. Ecological Management Practices (EMPs) provide nature-based solutions for reducing flood risks in a sustainable and economically viable manner. However, in the rapidly urbanizing setups in developing nations, the application of EMPs is limited due to space availability, data scarcity and limited funding. This study uses a Non-Linear Programming Optimization Technique to provide modelling solutions in optimizing the land-use and costs under EMPs to reduce flood risks in the Quebrada Aries watershed in the Municipality of Heredia in Costa Rica. Depending on the availability and ease of execution, a combination of three EMPs (bio-retention areas, infiltration trenches and green roofs) were tested. The effect of the application of derived optimal combinations has been analysed. The optimal combination of EMPs analysed for different channel capacity was able to reduce the peak discharge for the worst flood causing event of 50 years return period from 16.86 m³/s (under current land-use) to 9 m³/s, 9.51 m³/s, 8.38 m³/s and 9.13 m³/s in four hypothetical scenarios considered. In urbanized catchments, EMPs cannot be applied indefinitely to avoid floods. However, an optimal combination of EMPs can drastically reduce the requirement of large capacity drainage channels. This information can help policy-makers to analyse trade-offs between urban development and flood control measures. The study is suitable for other data-scarce regions as well.
The aging of sewer networks is a serious issue in urban areas because of the reduced functionality of the system that can have negative impact on the urban environment. Aging pipes are not water-tight anymore and they can leak untreated sewage or allow infiltration of groundwater. In the latter case, more frequent combined sewer overflows (CSOs) may occur. Generally, prompt intervention to repair damaged conduits is envisaged. However, in low-lying coastal regions, sewer systems may provide an unplanned drainage that controls the groundwater table from flooding the urban ground. Here, a study is presented to investigate the influence of the repair of damaged sewer on the water table of an urban shallow aquifer. Sewer and groundwater models were built to describe the effect of sewer replacement. Based on a real dataset, simulations were run for a city located along an estuary. Results show that the presence of infiltration into the sewer system increases the frequency of CSOs, which trigger the discharge of untreated sewage after a minor precipitation or even in dry weather conditions. As the sewer is repaired, CSO spills diminish occurring only upon significant precipitation. However, the water table rises and eventually, during the high tide, the groundwater floods the low-lying part of the city. Overall, this work highlights the susceptibility of shallow aquifers in coastal urban areas and suggests that they should be regarded in flooding predictions.
Root damage from urban street trees represents a substantial concern arising from the conflict between root growth and limited growth spaces. Nonetheless, the phenomenon of root damage, which threatens the safety of urban facilities, appears to have received little scholarly attention. Moreover, the effectiveness of some proposed measures for root damage prevention and control has not yet received consistent evaluation. Accordingly, this review aims to examine root damage, including its causes and available prevention and control measures. Urban trees are found to have a high potential to exert root damage on infrastructures when the following factors exist. These include large and mature tree, fast-growing trees, trees planted in limited soil volumes, shallow-rooted tree with buttress roots, trees whose diameter at breast height exceeds 10 cm, old and cracked road paving, high soil surface moisture content, short distances between trees and sidewalks (<2 to 3 m), and underground pipes that are already broken and made of metals or stones. The phenotypic traits of trees may be the primary factor causing root damage when there is a mismatch between the root-soil requirements of urban street trees and the actual soil environment. The poor effectiveness of root damage prevention and control measures may be attributed to the lack of connection between the development of control measures and the mechanism of root damage.
An increasing number of businesses is funding tree planting. Several intermediaries intervene between the funding company and those planting trees, each playing a specific role. To ensure quality tree planting, intervention and leverage points need to be identified. We aim to understand the chain between the corporations that finance tree planting and those planting trees. We reviewed 61 multinational companies from France, Switzerland and the UK, involved in tree planting, and identified the partners with whom they work to attempt to characterise this chain. Our results show that there are at least eight different functions starting with the multinational company, then financiers, regulators, quality controllers, enablers, project developers, brokers and finally, implementers. Most corporations mobilise three to four actors or levels to carry out tree planting. The multiplicity of actors is both positive (e.g., quality assurance) and negative (e.g., adds costs). Growing pressure for corporations to demonstrate social and environmental responsibility signifies that more tree planting is likely. Yet, many challenges exist in this sector, which we aim to describe. Critical challenges we identify include transparency, equity and quality. In conclusion, this booming multilayer sector should be better structured; understanding the actors and their respective roles provides a first step in this direction.
Urban tree planting initiatives have been blooming worldwide to help tackle climate change and nurture healthy living environments for people and biodiversity. Many initiatives are characterized by ambitious targets based on the number of trees planted but are not defined by clear objectives, which hampers the success of these initiatives in achieving the desired benefits. Growing an urban forest is a long-term endeavour that requires sustained commitment and support by urban communities to fully realize the provision and even distribution of multiple benefits. In this perspective article, we discuss the characteristics of tree planting initiatives and argue they should be better connected to urban forest management objectives. We propose seven principles that can help improve the success of tree planting initiatives by ensuring that the right types of trees are planted where they are needed most and where they will have the greatest impact. These principles include: (1) connecting initiatives with long-term management, including defining desired benefits, objectives, targets, and indicators; (2) facilitating community engagement on tree planting and maintenance; (3) focusing on tree canopy cover targets rather than on the number of trees planted; (4) focusing on post-planting care and encouraging retention of existing trees; (5) monitoring tree losses and gains to determine whether the specified targets are being met; (6) increasing species diversity, through careful species selection, as well as age and size diversity to enhance urban forest resilience; and (7) addressing the inequitable distribution of tree canopy, specifically where low tree cover overlaps with socioeconomic needs.
Environmental pollution induced by heavy metals has been identified as a leading threat in the modern era. Woody tree species may play a crucial role in the removal of heavy metals from soil and air, thus minimizing pollution potential. The present study was designed to evaluate the phytoremediation potential of six tree species; Azadirachta indica, Cassia fistula, Conocarpus erectus, Eucalyptus camaldulensis, Morus alba, and Populus deltoids, respectively, in the industrial and residential areas of Faisalabad based on the concentrations of lead (Pb), zinc (Zn), cadmium (Cd), and copper (Cu) in their leaves and barks in winter (2018) and summer (2019) seasons. The seasonal contents of heavy metals in both the leaves and barks of these trees decreased in the order of: Zn > Pb > Cu > Cd at both study sites. The highest heavy metal contents were recorded in the leaves and barks of trees grown in the industrial areas as compared to residential areas, with leaves and barks having higher contents of heavy metals in the summer than winter. The tree species exhibited significantly different capacity for heavy metal accumulation, with the accumulation of Cd decreased in the order of: E. camaldulensis > M. alba > C. erectus > A. indica > P. deltoids > C. fistula, and while the order varied for different heavy metals. Overall, M. alba, E. camaldulensis and A. indica performed well in accumulating the targeted heavy metals from the ambient environment. Among the six tree species grown commonly in Faisalabad city, M. alba, E. camaldulensis, and A. indica are recommended for the industrial and residential areas due to their phytoremediation capacity for heavy metals.
Youth growing up in places with more greenspaces have better developmental outcomes. The literature on greenspace and youth development is largely cross-sectional, thus limited in terms of measuring development and establishing causal inference. We conducted a systematic review of prospective, longitudinal studies measuring the association between greenspace exposure and youth development outcomes measured between ages two and eighteen. We searched Cochrane, PubMed, CINAHL, Scopus, and Environment Complete, and included prospective cohort, quasi-experimental, and experimental studies on greenspace and youth development. Study quality was assessed using a 10-item checklist adapted from a previously published review on greenspace and health. Twenty-eight studies met criteria for review and were grouped into five thematic categories based on reported outcomes: cognitive and brain development, mental health and wellbeing, attention and behavior, allergy and respiratory, and obesity and weight. Seventy-nine percent of studies suggest an association between greenspace and improved youth development. Most studies were concentrated in wealthy, Western European countries, limiting generalizability of findings. Key opportunities for future research include: (1) improved uniformity of standards in measuring greenspace, (2) improved measures to account for large latency periods between greenspace exposure and developmental outcomes, and (3) more diverse study settings and populations.
In this paper, we present a study focused on the effect of sea level rise (SLR) on nuisance flooding due to groundwater (or groundwater flooding). A densely populated coastal urban area along a river estuary was selected for this work. We developed a three-dimensional (3D) shallow unconfined aquifer model of the site. We calibrated it with field measurements and used it to predict areas prone to groundwater flooding under different SLR scenarios. Results show that the water table is controlled by the river level as well as by aging infrastructure such as aging combined sewer and drinking water networks which drain and recharge the unconfined aquifer. Steady-state simulations run considering current river level scenarios show a very shallow aquifer throughout the area and simulations under different SLR scenarios predict that the water table starts to emerge from the ground in the low-lying parts of the site for 0.4 m of SLR.
Overall, this work suggests that groundwater in coastal urban areas is regulated by anthropogenic and natural systems and is susceptible to climate change contributing to inundation together with marine flooding and intense precipitation.
This chapter explains the importance for nature-based solutions as resilience infrastructure of cities. It sets the scene for the challenges and opportunities
presented by a city-wide uptake and implementation of nature-based solutions as
integrative and systemic solutions to planning for urban resilience and sustainability. We present not only the origins and the reasons for preferring nature-based solutions over conventional grey infrastructure for dealing with climate change pressures
but also how different planning aspects of nature-based solutions need to be reconsidered, reimagined and thereafter, transformed. In conclusion, an outlook towards
future cities is given on revolutionizing urban planning practice through nature-based solutions.
Given a lot of elusive information on the use and implementation of Nature-based Solutions (NbS) in the Global South, this review provides a synthesis of the evidence on the: - (1) distribution of urban green technologies in form of arboriculture and urban agriculture as a part of NbS packages for the sustainability of cities against population growth and impact of climate change; and (2) options of integrating and mainstreaming various NbS packages into city development policies, planning processes, and decision-making agendas. The sustainability of urban green as part of NbS packages and the usefulness for improvement of livelihoods is determined by the spatial (geographical location) and temporal (time of action) scales, and socio-ecological and institutional factors. Various NbS packages have shown the ability for use as climate change adaptation measures throughout the world. These functions include protection from soil erosion, protection from inland flooding, buffering natural resources against drier and more variable climates, protection from coastal hazards and sea-level rise, moderation of urban heatwaves and effects of heat island, and managing storm-water and flooding in urban areas. Furthermore, the benefits of urban agriculture and arboriculture include use as sources of food and generation of income; improve recreation and social interactions, and the sustainability of biodiversity. They also mitigate the impact of environmental pollution and climate change through reduction of gas emissions and act as carbon sinks. While the starting capital and lack of policy on urban agriculture and arboriculture in many countries, the importance of the industry is inevitably a useful agenda especially in the Global South due to vulnerability to the impact of climate change. This review also suggests the inclusion of all institutions, governments, and relevant stakeholders to emphasize gender sensitization at all levels of planning and decision-making in food production and adaptation measures to climate change.
Urban areas are home to more than half the world’s population, but also habitats for a wide range of plant and animal species. While street trees in urban areas have been recognized as important for human well-being, however, how they can contribute to wildlife conservation is less explored. Here we compiled a database of street tree inventories in China, that included species diversity, abundance and origin information of street trees from 59 cities to explore how different cities rank with regards to the use of native and diversity of street trees, which are both considered beneficial to urban biodiversity. We found the most abundant species contributed an average of 35.8% of all street trees in the studied cities, and non-native species contributed an average of 40.6% of the street trees. Most cities are dominated by only a few species of trees, and a large proportion of these trees are non-native tree species, indicating that streetscapes are likely not friendly to biodiversity. Our proposed ranking schedule provides an easy tool for classifying cities according to their street tree wildlife friendliness, while also providing clear management directions on how to improve city tree composition for biodiversity conservation. To build a sustainable society in which nature and humans can coexist, we recommend that city planners should consider biodiversity conservation as a core value of urban planning. Specifically, we encourage the planting of more native trees and use of a more diverse set of species capable of attracting wildlife, thus promoting biodiversity in cities. Furthermore, awareness of biodiversity friendly tree planting systems needs special attention in developing regions and densely populated areas. We emphasize that more regional research needs to go into identifying local species that can be used as street trees while simultaneously functioning as wildlife attractants.
The alleviation of global poverty is a major objective of the 2030 UN Sustainable Development Goals (notably SDG1 “to end poverty in all its forms everywhere”). Many rural people experiencing poverty often rely on forests and tree-based systems, such as agroforestry, suggesting the existence of links between such systems and poverty outcomes. This paper reviews the evidence of such links across multiple dimensions of poverty and well-being, based on an expert panel convened by the International Union of Forest Research Organizations (IUFRO) and an extensive literature search. We consider whether, how, where, when, and for whom forests and trees in the wider landscape influence poverty dynamics. We organize the evidence according to four pathways through which forests and trees influence household poverty dynamics: 1) helping households move out of poverty; 2) maintaining well-being levels through subsistence, food security, health, and cultural and spiritual values; 3) preventing declines by mitigating risks and stabilizing consumption; 4) decreasing well-being by generating negative externalities that could trap or move households into poverty. We found that local context matters considerably, with the roles of forests and trees strongly varying across geographical, social, economic, and political settings. Another key finding is that evidence of forests and trees providing livelihood diversification and benefits that help households move out of poverty remains limited, based primarily on a small number of case studies. Evidence on the impact of gender gaps in relation to forest landscapes and poverty pathways is also lacking. However, our findings do suggest that ecosystem services provided by forests and trees play critical roles in maintaining well-being and food security and have the potential to contribute more to helping households move out of poverty and mitigating risks amplified by climate change. This review also highlights cautionary findings related to negative forest externalities that can maintain or move households into poverty. Together, these findings call for policy efforts to support the conservation and sustainable management of forest landscapes and agroforestry systems that are more targeted towards meeting the diverse needs of the rural poor. Our results also point to a need for greater effort to address gender disparities, which have been largely overlooked yet provide a critical opportunity to not only enhance gender equality but also advance sustainable poverty reduction goals.
Vegetation establishment in urban areas is a potential solution to combat elevated particulate matter (PM) pollution, create cleaner environment for residents and enhance the sustainability of cities. However, vegetation effect at the points of interest in street-canyon on traffic pollutant from multiple interconnected factors (e.g., plant species, vegetation configurations, aerodynamic effect, deposition effect and complex wind regimes) is still not well studied. Therefore, taking roadside vegetation and street canyon as research objects, we evaluated vegetation effect (VE) for vegetation configurations (VCs) with several tree species on the dispersion, deposition, and distribution of traffic generated PM pollutant under different wind regimes. Results showed that (1) the transportation and distribution of traffic PM pollutant were different from wind regimes; (2) total VEs varied from -88.3% to 25.5%, depending on different VCs and wind regimes; perpendicular wind had the best VEs, while oblique wind had the worst VEs among the three wind directions; VEs of cypress were better than pine and poplar; VEs of one side planting were better than two sides planting. (3) the optimal VCs were found by each wind direction; two sides planting by shrub was suitable for parallel and oblique winds; for the perpendicular wind, the optimal VC was that two sides planting by cypress-shrub and increased canopy volume in the street center; and (4) VE were significantly correlated (P<0.05) with vegetation parameters at lower wind speed, however, no correlations were found at higher wind speed under parallel wind; leeward wall VEs were significantly correlated with aerodynamic parameter (P<0.001) while windward wall VEs and pedestrian-level VEs with deposition parameter (P<0.05) under perpendicular wind; VEs were significantly decreased (P<0.001) with aerodynamic parameter under oblique wind. The study highlights the impact of urban vegetation on air environment and provides insights for vegetation establishment from the viewpoint of improving air quality.
As drought variability increases in forests around the globe, it is critical to evaluate and understand ecosystem attributes that ameliorate drought impacts. Trees in arid and semi‐arid ecosystems can sustain tree growth and transpiration during drought by accessing shallow groundwater, yet the extent to which groundwater influences forest growth and transpiration in humid environments has largely been unexplored. We quantified groundwater’s influence on tree growth and transpiration in Northern humid forests with sandy soils. We hypothesized that even in wet regions, soil droughts occur relatively frequently in forests with sandy soils and result in water stress and reduced tree growth. Further, we hypothesized these reductions in productivity are ameliorated if the forest can access shallow groundwater during dry conditions. We evaluated tree growth responses using tree cores in Pinus resinosa trees and estimated forest groundwater use from diel water table fluctuations across sites covering a 1‐9 m depth to groundwater (DTG) gradient. In areas of shallow groundwater (DTG<2.5 m), we observed twice as much tree growth and high, frequent groundwater use (up to 81% of non‐rainy summer days). Groundwater’s influence on tree growth and transpiration declined as groundwater deepened along the DTG gradient in the range 1‐5 m below land surface. These findings suggest that water provided by a shallow watertable subsidizes evapotranspiration in humid forests and results in enhanced tree growth. Our research provides a basis for understanding the role of groundwater in conferring drought resistance in humid forests to help guide sustainable water and forest management decisions.
The present study aims to trace out the signatures of seawater intrusion into the
groundwater and the irrigation hazards in the coastal region of West Bengal, India
based on 56 groundwater samples. The result reveals that 48.21 % of the groundwater
samples have exhibited the values of seawater mixing index greater than 1 indicating
the effect of seawater mixing into the fresh groundwater. The electrical conductivity
(EC) in the studied samples ranges from 338 to 4330 µS/cm and as per the United
States Salinity Laboratory (USSL) classification of EC for irrigation water quality, about
31% of samples come under medium (251-750 µS/cm), 53% under high (751-2250
µS/cm), and 16 % under very high (2251-5000 µS/cm) salinity hazard classes.
Besides, the potential salinity (PS) reveals that about 52 % of samples have high
salinity problems while 16 % are moderately suitable (water may be used for medium
to coarse-textured soils) and 32 % are suitable which can safely be used for fine and
medium, and coarse-textured soils. The problem of salinity intrusion acts as a catalyst
to impair agricultural practice. For example, the average yield of rice production is low
(1.5 - 2.0 t ha-1) for South 24 Parganas compared to the neighbouring districts. The
study finds that ~ 49 % of samples having Na+/Cl- ratio greater than 1 indicates that
silicate weathering is the dominant process controlling groundwater hydro-chemistry
and sodium concentration. Moreover, a higher sea-level rise (3.90 ± 0.13 mm a-1),
frequent storm surge (142 events of moderate to severe cyclone during 1582 to 1991)
and overexploitation of groundwater and fall of piezometric level (e.g. 10.96 m in
1956- 2005 at Gobra, Kolkata) are major driving forces of seawater intrusion.
Afforestation can reduce desertification and soil erosion. However, the hydrologic implications of afforestation are not well investigated, especially in arid and semi-arid regions. China has the largest area of afforestation in the world, with one-third of the world’s total plantation forests. How the shrubs affect evapotranspiration, soil moisture dynamics, and groundwater recharge remains unclear. We designed two pairs of lysimeters, one being 1.2 m deep and the other one 4.2 m deep. Each pair consists of one lysimeter with bare soil, while on the other one a shrub is planted. The different water table depths were implemented to understand how depth to groundwater affects soil moisture and water table dynamics under different hydrological conditions. Soil moisture, water table depth, sap flow, and rainfall were measured concurrently. Our study confirms that for the current meteorological conditions in the Ordos plateau recharge is reduced or even prohibited through the large-scale plantation Salix psammophila. Shrubs also raise the threshold of precipitation required to increase soil moisture of the surface ground. For the conditions we analyzed, a minimum of 6 mm of precipitation was required for infiltration processes to commence. In addition to the hydrological analysis, the density of root distribution is assessed outside of the lysimeters for different water table depths. The results suggest that the root-density distribution is strongly affected by water table depth. Our results have important implications for the determination of the optimal shrub-density in future plantations, as well as for the conceptualization of plant roots in upcoming numerical models.
Climate change in combination with increasing urbanization is a major challenge for our cities. Ecosystem services from the urban green play a significant role in mitigating the negative effects. Urban tree growth models are appropriate tools for the quantification of ecosystem services in some cases in dependence of the plant growth dynamics and of the changing environment. We report about the state of the art in modelling urban tree growth and ecosystem services and describe the background of urban tree growth and the provision of ecosystem services. Furthermore, we present basic growth model principles and describe and compare existing urban tree growth models. Finally we discuss the use of urban tree growth models, uncover advantages and disadvantages of the single urban tree growth models and indicate current limitations and future venues in modelling.
The provision of ecosystem services is a prominent rationale for urban greening, and there is a prevailing mantra that 'trees are good'. However, understanding how urban trees contribute to sustainability must also consider disservices. In this perspective article, we discuss recent research on ecosystem disservices of urban trees, including infrastructure conflicts, health and safety impacts, aesthetic issues, and environmentally detrimental consequences, as well as management costs related to ecological disturbances and risk management. We also discuss tradeoffs regarding species selection and local conservation concerns, as well as the central role of human perception in the interpretation of ecosystem services and disservices, particularly the uncritical assertion that 'everybody loves trees'. Urban forestry decision-making that fails to account for disservices can have unintended negative consequences for communities. Further research is needed regarding life cycle assessments, stakeholder decision-making, return-on-investment, and framings of services and disservices in urban forestry.
Coastal shoreline forests are vulnerable to seawater exposure, the impacts of which will increase due to sea-level rise, but the long-term adaptation strategies and vulnerability of coastal forests are not well understood. We used whole-tree transpiration, leaf water potential, tree-ring width, and tree-ring δ 13 C (a proxy for intrinsic water use efficiency, iWUE) to examine the long-term adaptation strategies of red maple (Acer rubrum) trees at the coastal interface (i.e., shoreline) and nearby upland in Maryland, USA. Red maple trees that grew along the shoreline and were exposed to slightly saline water (up to two PSU) had higher transpiration rates than those growing in the nearby upland forest during a wet year, but these differences disappeared during a normal precipitation year. Shoreline trees grew more slowly than upland trees over the last four decades, but these growth differences have disappeared in the last six years. Shoreline and upland red maple trees had similar variation in iWUE, indicating that higher transpiration rates of the seawater-exposed trees did not translate into differences in water use efficiency. There were no differences in predawn and midday water potential between upland and shoreline trees, suggesting no additional water stress occurs in shoreline trees. These findings indicate that mature red maple in our coastal study site maintains gas exchange and growth at a consistent or homeostatic level under slight soil salinity.
This review paper is the first that summarizes many aspects of the ecological role of trees in urban landscapes while considering their growth conditions. Research Highlights are: (i) Plant growth conditions in cities are worsening due to high urbanization rates and new stress factors; (ii) Urban trees are capable of alleviating the stress factors they are exposed to; (iii) The size and vitality of trees is related to the ecological services they can provide. Our review shows, in a clear way, that the phenomenon of human-related environmental degradation, which generates urban tree stress, can be effectively alleviated by the presence of trees. The first section reviews concerns related to urban environment degradation and its influence on trees. Intense urbanization affects the environment of plants, raising the mortality rate of urban trees. The second part deals with the dieback of city trees, its causes and scale. The average life expectancy of urban trees is relatively low and depends on factors such as the specific location, proper care and community involvement, among others. The third part concerns the ecological and economic advantages of trees in the city structure. Trees affect citizen safety and health, but also improve the soil and air environment. Finally, we present the drawbacks of tree planting and discuss if they are caused by the tree itself or rather by improper tree management. We collect the latest reports on the complicated state of urban trees, presenting new insights on the complex issue of trees situated in cities, struggling with stress factors. These stressors have evolved over the decades and emphasize the importance of tree presence in the city structure.
Sap flow sensors are crucial instruments to understand whole-tree water use. The lack of direct calibration of the available methods on large trees and the application of several data-processing procedures may jeopardize our understanding of water uptake dynamics by increasing the uncertainties around sensor-based estimates. We directly compared the heat ratio method (HRM) sap flow measurements to water uptake measured gravimetrically using the cut-tree method on a large mature aspen tree to quantify those uncertainties for ten consecutive days. The influence of the azimuthal position of the sensors and the application of different data-processing procedures on the accuracy of the sap flow sensors’ estimates was assessed using different metrics. Overall, the sap flow measurements showed high temporal precision with the gravimetric data. Azimuthal and radial variability of measured sap flux density showed the most substantial effect on the accuracy of the sensors’ estimates of whole tree sap flow. The zero-flow corrections applied altered the accuracy and linearity of the sensors’ measurements at the hourly scale, while the sapwood area method used had a lesser impact. Across the ensemble of available data-processing procedures, the cumulative whole-tree water uptake estimates for five consecutive days from the sensor diverged from the gravimetric measurements by less than 1% to more than 50% depending on the sensors azimuthal position and data corrections applied. This study illustrates some of the uncertainties associated with the methodological approaches chosen when using sap flow sensors to estimate water uptake in tall and large diameter trees.
Urban development induced land transitions affect urban hydrology, resulting in increased flooding risks. Climate change-related precipitation changes are an added complexity to the flood risks of cities. This study examines the role of land use changes in determining the occurrence of urban flooding events across 42 Indian cities under current and future climate change scenarios. Landsat images for 1990, 2000, 2010, and 2017 have been processed using a hybrid classification technique to determine the land use shares for all cities. A typical event-count study using newspaper archives has been conducted to create a flooding event database. A multilevel model employing logistic mixed-effects approach was used. Future projections of the occurrence of flooding events for nine models under three climate change-related Representative Concentration Pathways (RCPs)—2.6, 4.5, and 8.5—and three urban development scenarios have been carried out. The results suggest that cities should preserve the land uses that act as a sponge—the green, open and blue spaces. As these spaces decrease, the projected flooding events increase. Under the RCP 2.6 scenario, the number of flooding events is significantly lower (95 % confidence) than under RCPs 4.5 and 8.5. The expected flooding occurrences between RCP4.5 and RCP8.5 are not significantly different (95 % confidence) for many scenarios, suggesting that Indian cities should aim for a world temperature increase of below 2 °C, or devastating consequences are imminent. This study highlights the need for Indian cities to undertake integrated spatial planning measures for a resilient, sustainable urban future.
Ethnopharmacological relevance:
The genus Tamarix L., with the common name of tamarisk, consists of more than 60 species of halophyte plants which are used for medicinal purposes such as infections, wounds, and liver and spleen disorders by local people mostly in Asian and African countries.
Aim of the review:
In spite of the potential health benefits of Tamarix spp., the plant is not yet well-known in modern medicine; thus, the aim of the present review is to provide a critical appraisal of the current state of the art regarding the ethnomedicinal uses, phytochemistry, and pharmacological properties of Tamarix spp.
Materials and methods:
Electronic databases (Medline, Cochrane library, Science Direct, and Scopus) were searched with the words "Tamarix" and "Tamarisk" to collect all available data regarding different Tamarix species from the inception until May 2019.
Results:
Tamarix spp. is traditionally used for gastrointestinal disorders, wounds, diabetes, and dental problems. Phenolic acids, flavonoids, and tannins constitute the main phytochemicals of these plants. Preclinical pharmacological evaluations have demonstrated several biological activities for Tamarix spp. including antidiabetic, hepatoprotective, wound healing, and anti-inflammatory; however, no clinical evidence have yet been provided to support the health benefits of these plants.
Conclusions:
Tamarix spp. are plants rich in polyphenolic compounds with valuable medicinal properties; though, there are several methodological problems such as lack of a mechanistic approach and taxonomic ambiguities in the current available data. High-quality preclinical studies, as well as well-designed clinical trials are necessary to confirm the safety and efficacy of these plants in humans.