Semi-arid Urban Area Research Articles

Carbon Sequestration and Storage of Urban Trees in a Polluted Semiarid City

Cities play a critical role in anthropogenic CO2 emissions, which exacerbate climate change and impact urban populations. Urban green infrastructure, such as urban trees, provides essential ecosystem services, including reducing atmospheric CO2 levels. However, there is a significant knowledge gap regarding the impact of urban trees on climate change in semiarid, polluted cities like Tehran, the capital and largest metropolis of the Middle East. This study assesses the carbon sequestration and storage potential of Tehran’s urban infrastructure using the i-Tree Eco model. A randomized cluster sampling method was employed, collecting data on species composition, diameter at breast height (DBH), and total tree height. The results indicate that Tehran’s urban trees sequester approximately 60,102 tons of carbon per year, equivalent to 220,393 tons of CO2. The net carbon storage in urban trees is about 254,579 tons, equivalent to 933,455 tons of CO2. Parks and urban green spaces demonstrate the highest rate of carbon sequestration per hectare, followed by urban services land use. Prioritizing the planting of species with high sequestration rates like Cupressus arizonica (Arizona cypress) and Cupressus sempervirens L. var. horizontalis (Mediterranean cypress) could enhance carbon sequestration efforts in Tehran. These data provide valuable insights into the carbon sequestration potential and environmental impact of different land use types, and may aid in the development of effective environmental policies and land management strategies in semiarid urban areas and other cities in similar settings.

Identifying the barriers to green infrastructure implementation in semi-arid urban areas using the DPSIR framework: A case study of Amman, Jordan

Research has highlighted the role of green infrastructure (GI) in addressing climate change impacts and other societal and environmental challenges in semi-arid urban areas. Regardless of this potential, GI implementation and research in arid climate zones is limited. Accordingly, using Amman, Jordan as a case study, this research aims to investigate the barriers that impede and prevent GI implementation in semi-arid urban areas. The GI barriers are conceptualized using the Driving–Pressure–State–Impact–Response (DPSIR) framework which was applied on data collected from semi-structured interviews with GI stakeholders in the city. The findings highlighted 17 general implementation barriers grouped into 6 categories. The DPSIR framework specifically highlighted the role of natural and human drivers (e.g. rapid urbanization, institutional capacities, and lacking financial resources) in creating significant barriers to GI implementation. It also illustrated the focus on open spaces and green cover in GI planning in Amman, lacking performance data on GI best practices in semi-arid contexts, and the need of integrated pathways to overcome the identified barriers. The DPSIR framework presents an easy-to-communicate picture of the state of GI implementation in the city that can be utilized by decision-makers, particularly those lacking access to diverse resources. The outcomes of this study enhances our understanding of GI planning in semi-arid urban areas and are beneficial for policymakers and practitioners looking for pathways to promote resilient urban development strategies. Overall, the study calls for further GI research on semi-arid developing contexts.

Energy estimation of FSPV-based microgrid for sustainable electricity generation and water conservation in hot semi-arid urban areas

Energy estimation of FSPV-based microgrid for sustainable electricity generation and water conservation in hot semi-arid urban areas

Exploring potential trade-offs in outdoor water use reductions and urban tree ecosystem services during an extreme drought in Southern California

In Southern California cities, urban trees play a vital role in alleviating heat waves through shade provision and evaporative cooling. Trees in arid to semi-arid regions may rely on irrigation, which is often the first municipal water use to be restricted during drought, causing further drought stress. Finding a balance between efficient water use and maintaining tree health will be crucial for long-term urban forestry and water resources management, as climate change will increase drought and extreme heat events. This study aimed to quantify how urban tree water and carbon fluxes are affected by irrigation reductions, and how that relationship changes with tree species and temperature. We used an ecohydrologic model that mechanistically simulates water, carbon, and energy cycling, parameterized for 5 common tree species in a semi-arid urban area. We simulated a range of irrigation reductions based on average outdoor water use data from the city for a recent extreme drought as well as with warmer temperatures. We then analyzed the response of model outcomes of plant carbon fluxes, leaf area index (LAI), and water use. Results show that reducing irrigation up to 25%, a comparable amount as the California state mandate in 2014, has minimal effects on tree primary productivity and water use efficiency. We found that transpiration was linearly related to irrigation input, which could lead to a short-term loss of evaporative cooling with irrigation reductions during drought. However, primary productivity and LAI had a nonlinear response to irrigation, indicating shade provision could be maintained throughout drought with partial irrigation reductions. Results varied across tree species, with some species showing greater sensitivity of productivity to both irrigation reductions and potentially warmer droughts. These results have implications for water resources management before and during drought, and for urban tree climate adaptation to future drought.

Design parameters influencing the energy performance and indoor comfort of net zero energy building “NZEB” designed for semi-arid urban areas: Digital workflow methodology, sensitivity analysis and comparative assessment

In order to reach carbon neutrality targets in the built environment, worldwide designers should look toward more sustainable buildings, especially with solar integrated configurations to reduce the reliance on conventional sources of energy in urban environments.In this paper, a parametric digital workflow developed in the Grasshopper environment allowed the evaluation of the energy performance and indoor thermal and visual comforts of variable nearly Zero Energy office building configurations. More specifically, as a first step, this paper focused on the use of the global sensitivity analysis tool to evaluate the varying influence of different selected design variables on energy self-sufficiency and indoor thermal comfort of the office building. Then, based on the results of this investigation, we compared the energy performance of nearly/Net Zero Energy Buildings (ZEB) considering two opposing extreme design options, that are the worst and best configurations, using different timescales, i.e., annual, monthly, weekly, daily and hourly performances. Interestingly, the annual Solar Contribution Ratio (SCR), defined as the ratio between yearly solar production and the energy demand of the building, varies between 39 % and 146 %, while also maintaining an acceptable degree of visual indoor comfort (sDA > 0.5). Besides, the findings underscore the significant contribution of the BIPV system in shifting towards the net zero energy goal, accounting for as much as 57.14 % of the total solar energy output. Moreover, the energy self-sufficiency on an hourly basis reveals that the BIPV shading area enhances the daily load cover factor by a range of 4.39 % to 23.87 %, depending on the building’s design strategies and the season of the year.Overall, the research outcomes aim at evaluating the influence of a set of design inputs on quantitative indicators related to indoor visual, thermal comforts and energy performance that can provide practical information for building designers, urban planners as well as grid designers and operators. Also, this research provides understandable visual and graphical representations capturing the variation of the indexes in variable time-steps. Lastly, the result of this study proves that Net Zero Energy Building, even positive energy building, could be achievable within semi-arid climate conditions.

PM chemical characterization at a semi-arid urban environment in Central Mexico

The central part of Mexico, a semi-arid region, hosts many anthropogenic activities that might affect the air quality of the several large cities within; however, the processes that occur in its atmosphere are poorly understood. Here, we investigated the concentration and chemical composition of the particulate matter in the Metropolitan Area of Queretaro for one year, together with meteorological variables and other pollutants data. Seasonal concentrations were determined mainly by meteorology. The secondary components comprised the largest fraction of PM2.5, followed by resuspension and the typical primary combustion sources in an urban area. Regional processing played a very important role in the formation of secondary aerosols. Local oxidation producing nitrate and less oxidized organic aerosols occurred more rapidly at night, although photochemical production in the morning was also observed. These results represent the first report of long-term real-time chemical characterization with high time resolution in the region. In addition, they might be important for better understanding the production of secondary aerosols in other semi-arid urban areas.

CO2 flux dynamics of exotic and native species in an extensive green roof simulator with hydric deficit

The rise of urban greenhouse gas emissions creates the need to improve available mitigation strategies. The effectiveness of green roofs depends on their correct design, including vegetation choice. To this aim, we studied the performance of native and exotic plants in hydric deficit conditions of a semi-arid urban area, Bahía Blanca, Argentina, and their ability to sequester CO2. Three native (Poa lanuginosa, Sphaeralcea australis, and Phyla nodiflora) and three exotic (Oscularia deltoides, Sedum ´tokyo sun´, and Sedum nussbaunerianum) species were tested in an extensive green roof simulator with no irrigation. Exotics Oscularia deltoides and Sedum nussbaunerianum did not survive the fall, while Sedum ´tokyo sun´ survived until late spring. All native plants survived, but their growth was affected by the hydric deficit of the warmer months. Seasonal CO2 fluxes were detected, with the most C sequestration in the colder months. Warmer months had the highest CO2 release. Native Poa lanuginosa sequestered 2.2 times more CO2 than exotic Sedum ´tokyo sun´ and native Phyla nodiflora, showing that C sequestration depends on plant type and not hydric-deficit adaptation. Construction of extensive green roofs in semi-arid cities requires the use of native plants that can withstand large hydric deficits.

Potential for rain water capture in semi-arid urban areas

The semi-arid region of Paraiba is devastated by extreme climatic conditions, in which the low index and the irregularity of the rains are factors of great negative impact for the development of the region. We found in rainwater collection systems, an important alternative for the region, which can increase the volume of water available to a municipality, for the same rainfall regime. Therefore, one of the main objectives of the study was to estimate the Potential Volumes of Rainwater Capture (VPC) for the urban area of ​​São João do Cariri. These volumes will be estimated based on the proposed use of the city's impermeable surfaces as rainwater catchment areas for non-potable purposes. Such an estimation is important for the adequate dimensioning of cisterns, in order to guarantee the supply of thenon-potablewater demands of the population during the dry season.

Preliminary Model-Based Evaluation of Water Conservation Strategies in a Semi-Arid Urban Zone

The U.S. Environmental Protection Agency stormwater management model was applied to a semi-arid urban micro watershed. The sub-catchment’s current features were modeled as scenario A, while the insertion of a set of LID technologies (rain barrels, bioretention cells, permeable pavement, and infiltration trenches) was represented as scenario B. A third scenario (C), considering only the most feasible LID technologies, was also modeled. All the scenarios were evaluated under two representative storm events (30 and 9 mm in two consecutive days, and 39 mm of rainfall in one day) occurred during the sampling performed in this study. Water quality was also simulated for a 30-mm storm event and compared against field assessment results after a real 30-mm storm event. Through the model, the inefficiency of current evacuation methods after 30- and 39-mm storm events was demonstrated. Simulation of scenario B showed that LID technologies could satisfactorily diminish peak flows generated by the selected storm events as well as runoff-conveyed pollution, while the realistic scenario allowed a lower but satisfactory hydrological performance and almost the same runoff quality than scenario B. This preliminary study could contribute to spread awareness about the benefits of LID technologies in semi-arid urban areas of the developing world.

Feasibility of Rainwater Harvesting and Consumption in a Middle Eastern Semiarid Urban Area

Recent developments of Middle Eastern metropolitans, and the related soaring trend of population increase, is contemporary with the impacts of climate changes. This applies extra pressures to the centralized large-scale water treatment and distribution systems. Rainwater harvesting (RWH) for domestic urban activities can be a sustainable option of adapting with the rising demand of soft water in such an arid/semiarid area. A pilot system of rainwater draining and storage was constructed for alleviating parts of soft water scarcity in Mashhad, the second most populous city of Iran. Measurements were collected for two years at the drainage basin outlet and inside of a storage tank, which has been equipped for water harvesting purposes. We performed some preliminary stochastic analysis and evaluated probabilistic properties of the collected dataset, aiming to explain them with respect to the physical characteristics of the RWH system. Data clustering analysis confirmed that the quality of the water may change during rainwater draining and storage in the RWH tank. Particularly, sodium content of the sampled water in the drainage catchment illustrated higher variations, compared with the ones evaluated for the stored water in the reservoir tank. This can confirm that the quality of the stored water in the RWH reservoir is more stable than that obtained for each separate rainfall–runoff event. We assessed the potential of the harvested water in different consumption contexts, in light of some national and international water quality (physicochemical, biological, and toxic pollutants) guidelines. We relied on water quality indices (WQI) to interpret multiparametric properties of the collected rainwater from urban surfaces; consequently, the quality of the harvested water was categorized with moderate to almost good attributes. This makes it well suited for irrigation uses, which can play a relevant role against water shortages in the analyzed semiarid urban region. Otherwise, infiltration and treatments need to be performed if using harvested water for drinking consumptions (of human or livestock), some of which may be costly for local owners/uses. We provide some suggestions for improving efficiency of the system and enhancing the quality of the harvesting water.

Exploring the relationship between urban form and land surface temperature (LST) in a semi-arid region case study of Ben Guerir city - Morocco

Surface temperature is one of the critical factors used to study microclimate conditions through Land surface Temperature (LST), a widely used data source. This paper tests a classification approach using moderate spatial satellite resolution images to extract surface properties of Local Climate Zones (LCZs) in a semi-arid region against measured LSTs. However, LST is used to study and explore the spatial relationship between temperature and urban morphology. Therefore, it is considered an alternative and reliable data source to complement in-situ measurement, especially in developing countries.The used methodology is based on two statistical approaches: 1) auto-spatial correlation using Getis Ord Gi* statistic, and 2) ANOVA test. Results showed an inversion effect of surface urban heat island - SUHI, where a strong correlation between specific LCZs and the surface temperature was found. The urban classes represented by open-low-rise, compact-low-rise have shown a significant decrease in surface temperature for almost two decades and in both summer and winter seasons compared to non-urban ones.Therefore, the outcomes of this study may have critical implications for urban planners who seek to mitigate SUHI effects in arid and semi-arid urban areas. Also, the approach used in this study can be helpful to follow the urban environment's spatial and temporal development as an application framework of sustainable development.

Analysis of urban heat island characteristics and mitigation strategies for eight arid and semi-arid gulf region cities

The aim of the study is, therefore, to analyze the formation of the UHIs in eight different cities in arid and semi-arid regions. The analysis is based on land cover (LC) classification (urban, green, and bare areas). The study found that bare areas had the highest mean LST values compared to the urban and green areas. The results show that the difference in temperatures between the bare areas and the urban areas ranges between 1 and 2 °C, between the bare areas and green areas ranges between 1 and 7 °C, and between the urban areas and green areas ranges between 1 and 5 °C. Furthermore, the LST values varied for each of the LULC categories, and hence some areas in the three categories had lower or higher LST values than in other categories. Hence, one category may not always have the highest LST value compared to other categories. The outcomes of this study may, therefore, have critical implications for urban planners who seek to mitigate UHI effects in arid and semi-arid urban areas.

Effects of vegetation on the spatial and temporal variation of microclimate in the urbanized Salt Lake Valley

Land cover characteristics can produce changes in spatial and temporal variability in potential temperature (θ) at scales that are relevant to city inhabitants. Using data from 60 sensors positioned in five urban parks and surrounding residential neighborhoods in the semi-arid Salt Lake Valley, we evaluated the effect of turfgrass cover versus tree shading on spatial and temporal variation in microclimate in a semi-arid urban area. Our results indicated that the replacement of vegetation by impervious surfaces plays a role in microclimatic homogenization. Tree shading was associated with higher spatial variability of θ during the day, while turfgrass cover was associated with higher spatial variability of θ at night. Contrary to our expectation of tree shading governing daytime θ, we also found turfgrass cover to have an efficient cooling effect. This suggests a prominent role of turfgrass evapotranspiration enhanced by high atmospheric evaporative demand, high soil moisture availability, and increased radiation loads that are characteristic of semi-arid urban landscapes. Given that turfgrass cover was also associated with reduced θ at night, mixed tree and grass landscapes may be effective in alleviating the urban heat island effect in semi-arid urban settings.

Aerosol climatology and determination of different types over the semi-arid urban area of Tehran, Iran: Application of multi-platform remote sensing satellite data

In this study, the combination of multiple satellite data was used to improve the assessments of aerosol properties including the aerosol optical depth, Angstrom exponent, UV aerosol index, and single scattering albedo over a semi-arid urban area during the period from 2008 to 2017. The data sets were derived from MODIS and OMI. The critical threshold values for each of the aerosol properties have been defined according to the previous studies to determine different aerosol types.Results of long term analysis of aerosol properties show that all parameters present a distinct monthly variation. A slightly increasing trend is detected for aerosol index values and this indicates the presence of more absorbing aerosols in recent years. There also is an obvious, consistent cooling effect of aerosols based on the variation of single scattering albedo. The aerosol optical depth relative frequency histogram shows a wide range of values with a maximum of about 40% around the range of 0.3 which is generally higher than some other polluted cities in the world. However, the Angstrom exponent peak around 0.8 likely means the dominance of aerosols in coarse mode.The results of the determination of different aerosol type show that, right after the mixed type aerosols, the urban/industrial aerosol type is the second-highest contributor to the aerosol composition and that it is followed by dust aerosols. On the other hand, maritime aerosols and smoke, present in less than 5% of the days studied, do not have a significant contribution. Seasonal analysis of different aerosol types indicates the dominance of large absorbing aerosols, i.e. dust during summertime, and small aerosols with non-absorbing properties, i.e. urban/industrial aerosols, mostly during cold seasons.

A comparative analysis of day and night land surface temperature in two semi-arid cities using satellite images sampled in different seasons

Urban heat island (UHI) refers to the occurrence of very high temperature patches in urban areas with respect to surrounding rural areas. The behaviour of Land Surface Temperature (LST) with different land covers varies for day and night time in a given urban area. Therefore, an attempt has been made for the comparative analysis of the day and night LST in two semi-arid cities in India i.e. Ahmedabad and Gandhinagar using two Landsat 8 images (one for day and one for night time) for each city. The relations of day and night LST with three independent variables such as Normalized Difference Vegetation Index (NDVI), Normalized Difference Built-up Index (NDBI) and impervious surface fraction (ISF) were established using Landsat 8 data. Based on the relation of LST with indices, the combinations of indices were used for developing the models to improve the correlation of day and night LST with the land cover. The developed models improved the correlation of day and night LST with the combinations of indices as compared to the relation of LST with individual variables in semi-arid urban landscapes with reasonably good coefficient of determination (R2) values of 0.63 in Ahmedabad and 0.79 in Gandhinagar for day time. The reasonably good values of R2 were found to be 0.81 and 0.75 for Ahmedabad and Gandhinagar, respectively, for night time. The developed model was also evaluated using 12 MODIS satellite images i.e. six images of each city for the summer, post-monsoon and winter seasons (one for day and one for night time in each season). The results of the developed models showed high capability to explain LST in heterogeneous semi-arid urban area for both day and night time in the summer, post-monsoon and winter seasons in a year. However, the relations established in this study can further be investigated for other months and years to understand its significance for other dates in semi-arid urban areas.

An assessment of wastewater pollution, treatment efficiency and management in a semi-arid urban area of Pakistan

An assessment of wastewater pollution, treatment efficiency and management in a semi-arid urban area of Pakistan

The influence of roadside trees on the diffusion of road traffic pollutants and their magnetic characteristics in a typical semi-arid urban area of Northwest China

Leaf samples of Juniperus formosana were collected from an open road environment, in order to establish how particulate matter (PM) generated by vehicles was dispersed in both horizontal and vertical directions. Sampling was conducted at sites with trees of varying height and configuration adjacent to a major road in Lanzhou, Gansu Province, Northwest China. The concentration of remanence-bearing ferrimagnets in the leaf samples was estimated from measurements of Saturation Isothermal Remanent Magnetization (SIRM), while the weight of particles deposited on the leaves and their elemental composition were determined at different heights and in different directions relative to the road. The PM on the surface of needles was predominantly influenced by traffic emissions and by dust resuspension. Rows of roadside trees, as opposed to solitary trees, were more effective at intercepting PM and thus in filtering road traffic pollution. The results indicate that Juniperus formosana needles may be an effective bio-sensor for monitoring variations in the spatial diffusion of road pollutants.

Urban flood estimation and evaluation of the performance of an Urban Drainage system in a Semi-Arid Urban Area Using SWMM.

Estimation of urban runoff peak and volume is a fundamental step in determining the transferring capacity of urban drainage systems. The main aim of this study was to present an application of the Storm Water Management Model (SWMM) in order to estimate urban flooding of a semi-arid area (Zanjan city in the northwest of Iran). The performance of an urban drainage system in the study area was also investigated. According to the results, SWMM is an effective tool for urban flood estimation in a semi-arid area. In this study, urban peak flow was simulated via a calibrated model with acceptable accuracy. Based on the results of the model simulation, the capacity of the main canals in the study area is sufficient for peak runoff transferring for a design storm with 50-year return periods, without retrofitting. Whereas, based on local observation and model results, localized and surface flooding can be observed in some urban areas. PRACTITIONER POINTS: In this study, urban flooding of a semi-arid area located in the northwest of Iran was estimated via a water Management Model (SWMM). According to the results, the SWMM model has considerable predictive capability for runoff evaluation in semi-arid regions when it is correctly calibrated via measured data. Also Modeling results showed that the main urban drainage network of the study watershed has an acceptable capacity for transmitting the runoff and flood waters, however the large amount of building materials and garbage that have been dumped in the canals could cause inundation problems.

Reclaiming Suburbia: Differences in Local Identity and Public Perceptions of Potable Water Reuse

Urban water managers are increasingly interested in incorporating reclaimed water into drinking supplies, particularly in rapidly growing arid and semi-arid urban areas, such as the western United States. Northern Nevada is one location that is considering augmenting drinking water supplies with reclaimed water, a practice that is known as planned potable water reuse. Potable water reuse can expand water supply and reduce wastewater disposal. However, past studies have shown that the introduction of potable reclaimed water can be controversial and requires an understanding of public perceptions of the resource prior to implementation. This study explores the factors that influence whether or not respondents in northern Nevada express willingness to drink reclaimed water. We pay specific attention to the degree to which self-identification as an urban, suburban, or rural resident influences how people consider using treated wastewater for both potable and non-potable purposes. To address this, we conducted a survey to assess community perceptions of reclaimed water use and applications in northern Nevada in the spring of 2018. We find that years spent living in the home and a respondent being female are negative and significant predictors of being willing to drink reclaimed water, while having heard of reclaimed water before and self-identification as a suburban resident are positive and significant predictors. As the region becomes more developed, particularly in its growing suburbs, it is essential to understand the nature of the interests and concerns regarding water resources and the expanded use of reclaimed water.

The role of the water tankers market in water stressed semi-arid urban areas:Implications on water quality and economic burden

Population growth and development are associated with increased water demand that often exceeds the capacity of existing resources, resulting in water shortages, particularly in urban areas, where more than 60% of the world's population resides. In many developing communities, shortages often force households to depend on water tankers amongst other potential sources for the delivery of water for domestic and/or potable use. While water tankers have become an integral part of the water supply system in many countries, the sector is often unregulated and operates with little governmental supervision. Users are invariably unaware of the origin or the quality of purchased water. In an effort to better assess this sector, a field survey of water vending wells and tankers coupled with a water quality sampling and analysis program was implemented in a pilot semi-arid urban area (Beirut, Lebanon) to shed light on the environmental and socio-economic impacts of the water tanker sector. Total dissolved solids (TDS), chloride (Cl−), and microbial loads exceeded drinking water quality standards. While TDS and Cl− levels were mostly due to saltwater intrusion in coastal wells, tankers were found to be a significant source of total coliforms. Delivered water costs varied depending on the tanker size, the quality of the distributed water, and pre-treatment used, with a markup of nearly 8–24 folds of the public water supply and an equivalent economic burden of 16% of the average household income excluding environmental externalities of water quality. The study concludes with a management framework towards consumer protection under integrated supply and demand side measures.