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Uncontrolled urban expansion with rapid population growth causes great pressure on the urban environment. The index of impervious surface area (ISA) has recently been used for the dynamic monitoring of urban expansion. This paper takes Dar es Salaam, the largest city in Tanzania, as an example, combined with multi-source data to obtain urban impervious surface component data on an annual scale, based on which the spatial–temporal characteristics of the city’s expansion are concluded: first, urban expansion showed an evidently phased pattern, with a steady annual growth rate of 2.9% during 2000–2005, and a low rate of 1.4% during 2006–2010, then a relatively high rate of 3.3% in the period of 2011–2019. Secondly, urban expansion hotspots emerged in areas along the main roads extending from the center to the south and north, but coastal expansion and infilling development became evident after 2015, with the impervious surface significantly increasing in areas with poor traffic. Third, urban land expansion, which lags significantly behind population growth, has eased, as the ratio of population growth rate to land expansion is declining, from 2.9 in the period 2002–2012 to 2.0 in the period 2012–2019. Finally, the influence of population, economy, traffic and nature on the evolution of impervious surfaces are analyzed. This paper puts forward corresponding strategic suggestions for land-use policies and analyzes the trend of urban growth spatiotemporal patterns in the future.

Tanzania is the only country bordering all three transboundary East African Great Lakes, i.e., Lake Victoria, Lake Tanganyika, and Lake Nyasa (Lake Malawi). This study investigated the spatiotemporal variability of basic physicochemical parameters of nearshore surface waters in Mwanza Gulf (Lake Victoria), Kigoma Bay (Lake Tanganyika), and Wissmann Bay (Lake Nyasa). Water quality was evaluated using the water quality index (WQI) method. Results showed that N and P nutrient pollution was relatively severe in central and southern parts of Mwanza Gulf owing to external agricultural emissions and internal release associated with physically disturbed sediment resuspension. External inputs from inflowing surface runoffs from the city of Mwanza typically enhanced N loading in northern parts of the gulf during the rainy season. Poor water quality was found in central and southern parts of Mwanza Gulf, especially in the rainy season. Algal blooms and NH

Nitrogen (N) is an essential nutrient element for life, and also a major element involved in the composition of greenhouse gases, surface water pollutants, air pollutants, etc. Quantifying and evaluating the nitrogen budget of a region is very important for effectively controlling the nitrogen discharge and scientifically managing the nitrogen cycle. In this paper, the urban Rural Complex N Cycling (URCNC) model was used to analyze the nitrogen budget of Mwanza region, a typical lakeside area with insufficient data, and the nitrogen flow process of livestock subsystem, cropland subsystem, human subsystem and landfill subsystem was clearly described and the nitrogen input sources of atmospheric subsystem and surface water subsystem were clarified. And the results demonstrated: (1) the cropland subsystem was the subsystem with the largest nitrogen flux, and the input, output and accumulation of nitrogen were 33,116 t of N, 31,925 t of N and 1191 t of N, respectively. Livestock subsystem was the second largest subsystem of nitrogen flux, and the input, output and accumulation of nitrogen were 31,013 t, 30,183 t and 830 t, respectively. The nitrogen flux of the human subsystem was also large, and the nitrogen input, output and accumulation were 17,905, 17,125 and 780 t, respectively. The nitrogen input, output and accumulation of the landfill subsystem were 3700 t, 770 t and 2930 t, respectively. (2) 8093 t of N, 6864 t of N, 3959 t of N, and 758 t of N emitted into the atmospheric subsystem from the livestock subsystem, cropland subsystem, human subsystem, and landfill subsystem, respectively. (3) The total Nr input of surface water subsystem increased from 18,545 t of N in 2010 to 20,174 t of N in 2020, with an increase of 8.78 % in the past decade. It was estimated that by 2030, the total Nr input of the surface water subsystem would reach 24,946 t of N with an increase of 23.65 % compared with 2020. The livestock subsystem was the largest source, the cropland subsystem was the second largest source and human subsystem was an important source. (4) Population growth, economic development and urbanization are the main nitrogen driving factor. (5) Technology and policy together have important contributions to the reduction of nitrogen pollution in surface water.

Anthropogenic pollution plays an important part in deteriorating the water quality of rivers all over the world, especially in urban areas of Africa where water quality monitoring is still seriously constrained by the limited test facility and capability. In this study, for evaluating the impact of urbanization on the river water quality, we investigated four typical urban rivers of Tanzania through the upper-urban-down gradient assessment approach and analyzed by water quality index (WQI) and statistical methods. The physicochemical indices monitored in these rivers revealed that the contents of those indicators of TN, TP, PO43−, NH4+, CODMn, and NO3− were accumulated significantly in the lower reaches of the cities, which indicated the life-type pollution characteristics in such urban rivers of Africa. The following main conclusions are achieved from this study. The water quality of 30% of the investigated river sections is in the medium to good status based on the subjective WQI with sensory factors included. Moreover, the sections with obvious water quality decline are mainly limited to the river segments within the urban central area, and severe pollution of water bodies is closely related to large cities, indicating an increasing pollution tendency with the quickly growing population. Therefore, to help formulate water pollution control policies in response to the rapid urban expansion in African countries, it is necessary to adopt an economical and feasible method to carry out early monitoring of surface water quality timely.

Rapid urbanization in developing countries has been accompanied by the spread of informal settlements, which is particularly prominent in sub-Saharan Africa. These settlements have become an important supplement to the inadequate formal housing supply in cities, and their spontaneously formed spatial patterns have important influences on sustainable development. In this study, qualitative and quantitative approaches were used to examine the morphological characteristics of informal settlements in Tanzania and the associated influences on urban development. Geographic spatial analyses, landscape pattern indices, and mathematical statistics, along with quick assessments, group discussions, and key informant interviews, were used to obtain detailed information on the spatial forms of informal settlements. The results indicate that the form of the settlements does not conform to the social, economic, or environmental characteristics of sustainable development. The disordered expansion of single-layered buildings with a single function, irregular road networks in poor condition, and a lack of consideration and protection of the ecological environment were found to negatively impact urban function and sustainable development. However, the structure and form of informal settlements could, in addition to formalization projects, be optimized to drive sustainable and socioeconomic development goals as well as environmental conservation.

Compact urban form has been applied as a strategy to reduce the loss of green space that occurs from development, but the impact of this policy on the provision of green space still presents many uncertainties. This research investigated the statistical relationship between urban form indicators and the loss of vegetation biomass to understand the response of quality green space provision to changes in urban morphology. A methodology combining multi-source data assimilation, statistical analysis, and spatial analysis was adopted for the Yangtze River Delta cities of China. First, six urban metrics were selected to describe the shape and layout of urban patches in each city, and the total biomass loss index was then introduced as a parameter. The values of urban metrics and total biomass loss index were calculated for the 50 Yangtze River Delta cities. Second, ordinary least squares regression and geographically weighted regression analyses were then used to establish a quantitative relationship between total biomass loss index and urban form indicators. The results revealed an extremely negative correlation between total biomass loss index and the three urban variables of Richard compactness, density gradient, and the Gini coefficient; moreover, the parameter estimates for the three variables in the geographically weighted regression model were local and varied over space. Third, the mechanisms by which the urban form influences biomass loss were discussed and different urban form planning strategies for particular urban areas were suggested. In conclusion, compact urban form in a clustered layout of urban areas with a dense central agglomeration was verified to be ecologically superior and conducive to green space protection. For the physical interpretation of the statistical relationship between urban morphology and vegetation loss, the interface effect of urban agglomeration on vegetation merits further study.

Developing countries are facing unprecedented urbanization coupled with informal peri-urban growth, characterized by inadequate basic infrastructure provision. A large proportion of peri-urban populations particularly in the Sub-Saharan African region faces limited access to drinking water. Informal water suppliers of varying size and scale have become predominant and fill drinking water supply gap left by public utilities. This paper draws on qualitative and quantitative research approach to examine the state, role and inherent practices of informal water supply system in addressing peri-urban drinking water shortages along with consumers and stakeholders' attitudes towards the system. Open-ended and semi-structured questionnaires were used to interview private water providers, public officials, households and other stakeholders to document informal water supply practices. The results indicate that informal small-scale providers account for 100% of drinking water in peri-urban settlements, but water infrastructures are in the dire state as its investment is carried out without adequate professional guidance. Furthermore over 64.1% of the communities acknowledged the importance of informal water providers in increasing water access. However, their recognition contravened with public institutions’ position where 60% maintained that public water provision remains a viable option for peri-urban water access. Nevertheless, overall condition depicts that informal small-scale water supply systems remain pertinent and leading drinking water access options for many households in peri-urban settlements. Acknowledging its contribution along with integration into public regulatory mechanism can greatly contribute towards the improvement of water supply services to the majority of informal urban and peri-urban populations.

Habitat quality (HQ) is of great significance to regional sustainable development, which is a key link for regional ecological security and human welfare. Assessing the temporal and spatial evolution of HQ caused by land-use change could provide a scientific basis for regional ecological protection and land management. Here, based on the ArcGIS platform and the InVEST model, this study quantified the spatial and temporal evolutions of land use, landscape patterns, and HQ from 1985 to 2015, in Taihu Lake Basin (TLB). Hotspot analysis tools were used to identify the spatial agglomeration and evolution characteristics of HQ in TLB. The results showed that, (1) the land use and landscape pattern in TLB experienced dramatic change process during 1985&ndash, 2015, with the dominating conversion being from farmland to construction land, which led to an increase in landscape heterogeneity and fragmentation. (2) The HQ was generally reduced in the past 30 years. In particular, the decline of HQ was extremely severe in the peripheral area of cities and roads, due to urban sprawl. (3) Regarding the spatial distribution of HQ, the northern and eastern areas were generally higher, while the western and southern areas were generally lower. The hotspots areas were mainly located in the southwestern mountain area and west-central lake area, while the cold spots areas were mainly located in urban areas in the north and the east. (4) The area and degree of habitat degradation were both increased significantly due to land-use change, and the degradation of the Taihu Lake was highlighted. Strengthening the ecological environment management and reducing the threat of urban expansion to the HQ is urgently required. This study could help understand HQ of the TLB and provide a scientific basis for decision-makers.

Land use changes in the tropics under the pressure of population growth have attracted wide attention. In this study, the riparian area with more settlements was selected to explore the land use temporal-spatial characteristics of the less developed Lake Tanganyika region. The study methods employed mainly included land use transition matrix, kernel density estimation, grid and buffer analysis of the ArcGIS software and remote sensing image processing. The changes of land use mainly reflected in the transformation between different land types, among which the conversion from forestland into arable land constituted the major event. Though the land use change rate was not so significant for the whole region, dramatic changes occurred around the towns especially in the northern area. It was found that a circle of arable land of about 6 km in width and more than 40% arable land density composed the farming hinterland of the major towns. Moreover, with the forest transition theory the change trends of land use and their influencing factors were analysed. The findings in this study should be helpful for the land use simulation and planning in similar riparian areas. For better understanding the dynamic of land use change, a future additional in-depth study at extensive spatial and temporal scale is appealed.

Many studies investigated the energy savings of buildings with green facades for different facade orientations and structures, whereas few studies have analyzed the influence of the urban form. This study evaluates the summer cooling energy savings of full-scale facade greening at blocks with different urban forms, using an integrated simulation with ENVI-met and EnergyPlus. Six idealized urban blocks (IUBs), each with two green-facade scenarios and one baseline bare-facade scenario, are established. The hourly output cooling loads of the bare- and green-facade scenarios are used to estimate the daily energy-saving rate (DER) and daily energy savings per m2 of green facades (DES). The results show that the block-scale facade greening provides a DER of 3.2–11% and a DES of 123–347 Wh/m2, representing a summer cooling energy reduction of 11–31 kWh for every m2 of the green facade. Among the six IUBs, the high-rise high-density site (HH) has the lowest DER and DES, and the mid-rise low-density site (ML) has the highest. A higher greening ratio (65%) results in a cumulative effect and a higher DER and DES than in the buildings with a lower greening ratio (35%). Shading provided by plants and substrates is the primary reason for the DES, whereas cooling and humidifying have relatively small influences, and a trade-off effect between the two is observed. The findings of this research can shed light on green-facade practices and building energy conservation in humid subtropical cities.

Phosphorus discharge in urban household consumption system has an important impact on the urban ecological environment, especially the surface water environment. In this study, a framework and its accounting model of phosphorus flow analysis in urban household consumption system by means of SFA (substance flow analysis) was constructed. Based on the accounting model, the flow of phosphorus in the urban household consumption system of Dar es Salaam was described quantitatively, and the results demonstrated: (1) the total phosphorus input, stock and output of urban household consumption system in Dar es Salaam were 4874t of P, 59t of P and 4815t of P, respectively. In terms of system input of phosphorus, residents’ food consumption had a decisive impact on the system’s phosphorus input (4765t of P, 97.76%), while the contribution of detergent to the phosphorus input of the system was small. In terms of system phosphorus output, human feces and urine phosphorus output accounted for the majority of the total system phosphorus output (2313t of P, 48.04%). The total phosphorus output of domestic garbage, wastewater and food processing loss were 1464t of P (30.41%), 561t of P (11.65%), 477t of P (9.90%), respectively. (2) There were 2314t of P discharged into surface water through human feces and urine and domestic wastewater, which had a negative impact on the prevention and control of surface water pollution. 34t of P came from scattered garbage storage and 315t of P came from centralized garbage storage due to limited treatment capacity of waste treatment plant. Centralized storage and decentralized storage increased the risk of further phosphate loss. (3) Accelerated urbanization, rapid economic development and low sewage treatment capacity would cause more phosphorus loss, and Dar es Salaam faced great challenges in P discharge reduction and pollution control. Finally, we proposed policy recommendations for P discharge reduction including the guidance to the reasonable dietary structure with low phosphorus, the promotion of cleaning products with less phosphorus and no phosphorus, and the construction of garbage treatment and sewage treatment infrastructure.

Green facades in cities have great potential for facilitating climate change adaptation and mitigation due to their well-documented energy and cooling effects. Many studies have reported that a green facade can noticeably reduce the building surface temperature and cooling loads in summer. However, little is known about the extent to which large-scale facade greening cools the ambient air or the relationship between the cooling effects and urban form. This research employed the ENVI-met model to evaluate the summer cooling effects of block-scale facade greening and their relationship with urban form in Nanjing City in China. Six idealized urban blocks (IUBs) representing typical urban forms in Nanjing combined with five hypothetical facade-greening ratios generated 30 scenarios for simulation. The results revealed a distinct spatial pattern of cooling effects in each IUB. The cooling intensity decreases with increasing elevation, and it is strongest in ground spaces on the downwind side. The maximum cooling intensity is 0.96 °C and observed in the high-rise high-density site (HH). Among the six IUBs, the low-rise high-density block (LH) appears to be optimal for facade greening since it ranks in the top 1–3 for the four cooling-effect indicators. The threshold values were evaluated to further estimate the minimum greening ratios required to achieve corresponding energy-saving targets in each IUB. The findings can provide insights into the cool air dispersion process in urban canyons that have varying geometries. Furthermore, the results can inform vertical greening practices for the determination of appropriate sites and coverage ratios.

This study assessed underlying natural and cultural determinants of tree health and ways to improve urban forest performance in compact Nanjing city. Two groups of factors were investigated: (1) habitat conditions, including planting site, ground-cover, land cover, and district; and (2) tree traits, including species provenance and seasonality, and tree dimensions. A stratified sampling strategy selected 6351 trees for detailed assessment. The data were analyzed by multivariate logistic regressions. Institutional, park-garden and industrial trees with more open-space sites with vegetated ground-cover performed better than roadside and residential ones. Poor trees in confined residential sites deviated from those in other cities. Park-garden sites did not always nurture meritorious, large and diversified trees. District differentiation in tree performance was related to land cover. Exotic and evergreen species grew better than indigenous and deciduous, offering hints on species-habitat matching. Detailed f...

Urban greenspaces are universally valued as amenity-recreation venues, wildlife refuges and essential livable-city ingredients. Western strategies of urban greenspace provision are difficult to implement or retrofit in most Asian cities, commonly constrained by a high-density compact form. With recent rapid urbanization and associated brown and green field developments, ample opportunities arise to overhaul greenspace standards and patterns. The case study of the ancient city of Nanjing in China permits planning for an integrated greenspace network, aiming at flexibility for future urban expansion, green field acquisition, recreational functions, wildlife habitats and environmental benefits. It consists of green wedges, greenways and green extensions that incorporate urban green areas at three landscape scales. At the metropolis scale, through normative and substantive analyses of urban form and urban expansion, and assessment of suburban uplands, five green wedges are demarcated to generate a star urban form. The green wedges link the extensive countryside to the central city, and define elongated finger-like spaces between them for urban expansion to avoid conflicts with green fields. At the city scale, three major greenways, including city-wall circular greenway, Inner-Qinhuai River greenway, and canopy-road greenway, are designed as a permeating framework to guide new greenspace location, configuration and continuity, and to link existing parks. These greenways are equipped with a comprehensive trail system to foster pedestrian and cycling movements that are preferred by the public and the government. At the neighborhood scale, a greenspace organization, consisting of residential public open spaces, shaded sidewalks and riparian strips, conforms to the network geometry. As well-connected entities, these small proximate enclaves provide opportunities for residents to have day-to-day contact with nature. They also serve to resist undue urban influences and intrusions. Overall, the three-tiered greenspace system provides an alternative mode for urban development to the conventional transport-dominated one, to usher substantial improvement in landscape-environmental quality and to augment the sustainable-city notion.

The urban landscape is by nature the result of many cultural and natural factors and processes. Cityscape associated with land attributes and human activities expresses a city's social and economic functions. Treescape in the form of species composition, tree dimension and tree performance echoes ecological and environmental functions. The cityscape can be denoted by urban factors, such as tree growing-space condition, tree management regime, human activities and planting history. The hypothesis that the cityscape plays a key role in molding the treescape is tested. Nanjing, an east China city notable for its high tree coverage, is chosen as the study area. A quantitative method has been developed to assess the relationship between cityscape and treescape. Based on statistical analyses on the surveyed results of 6527 trees and related cityscape attributes, this paper explores the pertinent patterns and underlying factors of treescape variations. Species composition has the strongest association with cityscape. Roadside and factories have lower species diversity. Residential and industrial land uses show smaller tree dimension. Trees in residential, commercial, heavy industrial land-uses perform below par. A three-way classification has been developed to examine the effects of urban factors on treescape at different cityscape scales. At the small scale, a well-vegetated groundcover will ensure better tree performance and a lower management burden. The medium-scale cityscape (land-use and habitat) is preferred in the study of treescape attributes and their spatial variations, and is suitable for urban tree planning and management.