Assessment and Ranking of Mashhad urban district to refer ecological quality of urban green spaces using Topsis method

IntroductionThe ecological benefits of green space is not limited only to absorption CO2 and producing O2, purifying air pollution, decreasing noise, improving soil condition and groundwater recharge and moderating microclimates and reducing the heat island effect in cities .But also by creation a living and dynamic system has improved urban ecological structure and function and promote the quality of the urban environment. Basically, green space is a part of urban Landscape structure which has an important influence on a wide range of ecological patterns and processes. As well as multiple social and economic benefits, Ecological value of urban green space can improve through synergies with the urban spatial structure and function. Spatial structure of landscapes is a central object of investigation in landscape ecology. This structure finds its expression in landscape pattern, which integrates both complex conditions of the natural environment. In order to landscape literature review, spatial structure is a major subset of the concept of spatial heterogeneity, usually referring to the spatial configuration of the system property. Ecological processes and the relationship between them can be identified by determining spatial configuration and urban green spaces composition. However, findings from the literature show that the quality concept was carried out by ecological and environmental variables. In particular, the quality of urban green space is defined by quantitative and qualitative factors, that if understood and analyzed properly, it can be concluded the concept of quality. Based on quality of life and attractiveness measures, it applied to urban green space when created delightful and beautiful environment for outdoor activities and provide key ecosystem functions and services as “green sources”. Strengthening ecological quality and ability provide species, nutrients and energy for “green sinks”. From ecological perspective, the explicit consideration of the quality is related to spatial structure and spatiotemporal interaction of processes in ecological research that involved the main contribution of landscape ecology to this paradigm shift. With an emphasis on structural aspects of landscape and urban green spaces, landscape ecology approach have provided a powerful tool to assess changing green patches and landscape. In this study, conceptualized framework of quality, based on landscape ecology approach and method which can facilitate the representation and analysis of changes and environmental processes and therefore, address the environmental quality and specify the requirements. By landscape ecology approach, we can interpret the effects of above-mentioned processes for environment ecological features and achieve a primarily classification of green space quality and function .According to this, the quality concept dependent on the nature of the ecological process that occurred in different level of scale, measured at the plot context analyzed in several time and displayed and represented in spatial patterns. Conceptually, landscape structure referred to spatial composition and configuration of environmental and ecological units and relationships among them. Due to the effects on ecological processes independently and interactively, the quality of landscape can be characterized by composition and configuration properties.
Material and MethodMashhad, the capital of Khorasan Razavi, is located in the northeast of Iran at latitude: 36°18′N 59°36′E. With an area of 382 km2 and current population 2.9 million, Mashhad is the second most populous city in Iran. In recent decades, it has witnessed rapid growth, mostly because of its economic, social and religious attractions. Due to the physical development of Mashhad in most areas, urban green spaces have been replaced with different buildings, so it is necessary to study urban green spaces in term of quality. Based on the divisions of Mashhad Municipality, it has 13 regions, which each of them, has different area, population and green spaces types and conditions. As quantity, Table 1 shows distribution of green space and urban parks.
Data processing and green space distribution mapSatellite images were utilized to derive urban green space maps. The detail of satellite image data (Landsat 8 ETM) used in this study obtained from the U.S. Geological Survey (USGS), dated on 21st June 2014. All image processing, classification and GIS analyses were performed using ENVI 4.7 software and Arc GIS 10. To provide a green space map, the unsupervised classification method was used to generate patch layer map (i.e., a polygon layer) in ENVI 4.7 software environment. Types and features were created based on integrated land use map and calculating and extracting the normalized difference of vegetation cover index (NDVI). To obtain a green spaces distribution map, the NDVI map was rectified and geo referenced by the Arc GIS 10.
Landscape metricsTo select and application the landscape metrics, previous studies have introduced landscape metrics according to objectives and methodology of research. Although, a series of landscape metrics, have been developed to characterize the spatial patterns of landscapes and to compare ecological quality across the landscapes, however, the number of metrics can be used in evaluating the ecological quality, but not all landscape metrics can easily be classified as representing landscape composition or landscape configuration. For example, mean patch size and patch density of a particular patch type reflect both the amount of a patch type present (composition) and its spatial distribution (configuration).
Rank and TOPSIS methodFor ranking and assessment of ecological quality, one of the MCDM methods named TOPSIS has been applied in this research. In this section, TOPSIS method is explained. TOPSIS (Technique for Order Preference by Similarity to Ideal Solution), developed by Hwang and Yoon, is one of the MCDA/MCDM methods for resolving real-world decision problems satisfactorily.TOPSIS attempts to indicate the best alternative that simultaneously has the shortest distance from the positive ideal solution and the farthest distance from the negative ideal solution. The positive ideal solution is a solution that tries to maximize the profit criteria and minimize the cost criteria, whereas the negative ideal solution is just opposite to previous one. The positive ideal solution is composed of all the good values attainable of criteria, whereas the negative ideal solution consists of all worst values attainable of criteria. In the TOPSIS method, precise scores that each alternative receives from all the criteria are used in the formation of a decision matrix and normalized decision matrix. By taking into consideration the rates of all attributes, positive and negative ideal solutions are found. By comparing the distance coefficient of each alternative, the preference order of the alternatives is determined.
Results and ConclusionUrban green space has many usages and benefits on quality of human life. The results indicate that green spaces of Mashhad have no adequate relative frequency and patches of green spaces have undesirable conditions in terms of spatial composition and configuration. Now it has no enough extent and continuity for providing ecological services and improving ecological quality. Appropriate distributions of patches are recognized in these areas, proximity of patches is extremely uniform and there is heterogeneous distribution of patches. There is no appropriate distribution of green space patches in other regions of the city; green spaces patches have been distributed non-uniformly and heterogeneous. Most patches are small and fragmentation is recognized, there are no appropriate ecological conditions, therefore there would be no appropriate ecological quality. Ranking ecological urban areas is done with TOPSIS. The results of this study showed that the best quality ecological area is 5 Mashhad And area 12 have the most undesirable ecological quality.