Remote sensing application for urban landscape assessment in arid regions (Case study: Yazd city, Iran)

Population growth and urbanization have caused many changes in land use and land cover that has been greatly affected by the structure, function and service of the ecosystem. Since 2008, more than half of the world's population has lived in urban areas, which, according to the United Nations, 80 percent of the world's population will be urban by 2050, and this continuous increase will lead to the rapid expansion of urban areas. Most of these cities are located in developing countries, especially in Asia and Africa, where a considerable part of them are arid and semi-arid countries. Estimates show that 85 percent of total Iran's lands are under arid and semiarid conditions climate. Arid areas with dry climate, poor vegetation, lack of water, limited rainfall and very fragile environment are identified. These characteristics cause the vulnerability of urban ecosystems. Considering that the function and performance of the environment depended on the composition and distribution of their structural elements, to better understand the dynamics of land, it is necessary to study the changes in spatial patterns. Information on land use changes over time can predict future changes and also be used to identify land a principled and sustainable design and planning,  also to determine the improper process of land change and prevent its spread. Landscape metrics can be used to identify this spatial pattern and it's change.  Applicability of landscape metrics is for the Quantifying of the landscape change and also it's used for analysis and planning of land uses. Metrics is a useful tool for designing and finding exact relationships between the structure and function of landscape functions. Accordingly, this study has tried to study and measure changes in landscape structure of Yazd city by using landscape metrics for three decades in this region from destruction and fragmentation of natural patterns and help planners and policymakers for the orientation of sustainable urban development. The aim of this study is to quantify and measure changes in spatial patterns of land use in Yazd city by using landscape metrics in two levels of class and landscape during the period of 27 years. Also, the distribution and composition of spatial patterns of land use have been investigated in two levels of green and built-up patches that have a major role in ecosystem function.

In this study, Landsat 5 at 1991 and Landsat 8 at 2017 satellite images have been used. After performing the necessary corrections on the satellite images, the classification was done using the maximum likelihood method. according to the diversity of vegetation in the area, three categories including bare land, vegetation and built-up were identified and classified. In order to investigate the accuracy of classification, error matrix and statistical parameters of the kappa coefficient and overall accuracy were used. The kappa coefficient and overall accuracy of the classification images for 2017  and 1991 are 0.81, 90%, 0.83 96%, respectively. The Fragstats 4.1 software was used to calculate the landscape metrics. In the present study, according to the aim of the study, Class Area (CA), Number of patches (NP), Percentage of Landscape (PLAND), AREA, Radius of Gyration (GYRATE), Euclidean Nearest Neighbor Distance (ENN), and Contagion landscape metrics (CONTAGE) were selected and evaluated at the class and landscape level.

In this research, by studying different metrics in the two scales of class and landscape, it was inferred that the landscape in open land and green spaces are being crushed and discrete over a period. While built-up has become more integrated and more expansive over the period, it shows the destructive effects of human activities on the environment. During the studied period, the highest increase in area to other classes belongs to the built-up class. In this study, the maximum number of patches is related to other classes of a green space class. The number of vegetation patches increased and the number of patches opens land and urban class decreased. The results of this metric along with area metrics show the phenomenon of fragmented in Yazd city. Changes in agricultural and gardening land use to residential areas cause disintegration of vegetation patches. The mean patch size of the built-up class has increased and in two vegetation and open land decreased. It shows that the impervious area in the studied city has increased. The average distance metric of each cell in the patches with the center of gravity in two classes of open land and vegetation decreased and the largest reduction is in the green space class. The Euclidean nearest-neighbour distance metric of patches in all uses has been increased which is related to open land.

The results of the study of metrics changes in the class area show that the built-up has increased by 4346.82 ha in the studied period. The reason for this is the increase in the population of Yazd city, which in 1991 and 2017 were 275298 and 529673  respectively. Therefore, more space is needed for the growth and expansion of the city, which causes the physical development of the construction. Due to the spatial expansion of the city, about 1667.61 ha of the agricultural lands and gardens in Yazd city has been destroyed and integrated into urban infrastructures. Increasing human infrastructure and activities without considering the capacity and ecological capability of this area can cause many environmental problems. Therefore, in order to prevent further degradation of the environment and reduce its quality. Monitoring and evaluation of land use patterns should be measured continuously so that they can be used as a guide to assess the current status of the urban ecosystem.