Assessment of the relationship between urbanization of Mashhad metropolis and geomorphic hazards susceptibility in the Middle Kashafroud Watershed

Introduction
Urbanization is affected by multiple variables such as geomorphic landform and landscape, population growth, economic growth, and geomorphic hazards. However, during urban planning and development, more emphasis is given to social and economic factors. Usually, the cities or region’s vulnerability to hazards is not properly assessed. Hence, in areas which lie in a rugged landscape, such as alluvial fan, slope area, alluvial plain, and pediment, geomorphic hazards such as landslide, land subsidence, flash flood, and debris flow can occur frequently. This can cause severe damage to human lives and their property. To avoid such scenarios, urban planners, decision-makers, engineers, policymakers should consider not only the physical urban environment but also its susceptibility to natural hazards. The Mashhad is the second largest metropolitan area in Iran with nearly 294 square kilometers. The Mashhad is located on northeast Iran. Mashhad is one of the Iranian metropolitan cities which is located in semi-arid with annual precipitation of 260mm, and mean annual temperature of 14 °C. The Mashhad has experienced a rapid growth in recent decades and has been suffering from geomorphic hazard. Nonetheless, no geomorphological practical analysis has been carried out for Mashhad. Due to its unbalanced development, it has many environmental problems. The Mashhad is highly migratory and suffers severely from informal settlements. Groundwater overexploitation due to population pressure stimulates the occurrence of geomorphic hazard such as land subsidence, and it urgently needs planned development and management of geomorphological structures. In this regard, the multi-hazard approach helps understand how hazards and vulnerabilities are combined over territory and gives a more accurate representation of the complexity of the risks for an area. This study investigated the urbanization impacts of Mashhad Metropolis and Geomorphologic Hazards with Emphasis on the Middle Kashafroud Watershed. In this regard, the physical development of Mashhad during a 20-year period (2003-2023) was first investigated and its development trend was predicted for the next 10 years (2033). Then, a comprehensive analysis of the relationship between the current and future physical development of Mashhad and its effects on the processes of landslides and subsidence has been presented. The results of this research, by improving comprehensive understanding of the environmental challenges, provide a pathway for urban planners and managers to increase urban resilience against these hazards.
Materials and Methods
This research was designed in three main steps with the aim of studying and predicting the relationship between the urbanization of Mashhad metropolises and geomorphologic hazards with emphasis on the middle Kashafroud watershed. In the first step, the physical development of Mashhad from 2003 to 2023 was investigated using Landsat satellite images and the maximum likelihood classification algorithm, and a land use map was generated. Then, using the Land Change Modeler (LCM) and Markov chain, the physical development trend of the city was predicted for the ten years (until 2033). In the second step, the landslide susceptibility assessment was evaluated using the weighted linear combination (WLC) method and analytical hierarchy process (AHP). Then, the land subsidence susceptibility assessment was estimated using the radar interferometry technique and Sentinel-1 images. Finally, the relationship between the physical development of Mashhad and changes in the processes related to landslides and land subsidence was analyzed.
 
Results and Discussion
Based on the results of the land use classification map, during the 20-year period, the urbanization has significantly developed. Agricultural land use has been decreasing. Rainfed agricultural land use, developed in the central and eastern parts of the Kashafroud watershed, increased in 2013 and decreased again in 2023. Poor pastures, which is covered the northern basin, significantly decreased in 2013 compared to 2003. Orchards, which are mostly spread along the valleys, especially in the southwest and northern basin, have decreased in recent years. Medium pasture is covered the southwestern areas. This type of land use showed a significant increase in 2013 compared to 2003, but it did not show much change compared to 2023. Other land uses, such as water bodies and fallow lands, have not changed during the 20 years; only fallow lands have slightly increased in 2013. The results showed that the physical development of the Mashhad metropolis is closely related to two geomorphic hazards, landslide and land subsidence. Slopes of the Binalood Mountain and Hazar Masjed Mountain in the southwest and northeast of Mashhad are prone to landslide due to sensitive geological structure and high erodibility of the rocks. Urban expansion towards the highlands and steep areas and along valleys, and the destruction of vegetation, increase the risk of landslide. On the other hand, land subsidence in Mashhad is mainly due to the overexploitation of groundwater resources and subsequently declining groundwater levels. The urban expansion in the southeast and northwest of the Mashhad plain have increased the vulnerability of these areas to land subsidence, so that in some areas the subsidence rate reaches more than 45 cm per year. This phenomenon is a serious threat to infrastructure, structures, and the urban environment.
 
Conclusion
The Mashhad metropolises exhibit the rapid and significant expansion in recent years. This physical expansion has occurred due to population growth, migration, economic and cultural development. However, this expansion has been accompanied by environmental, social, and economic challenges and consequences. A critical factor in managing these challenges is the integration of geomorphological aspects and its principles into urban planning. A comprehensive understanding of how geomorphological processes affect urban areas is crucial for developing effective and sustainable urban planning and management strategies. These solutions are particularly important in dealing with natural hazards, managing risks, and enhancing urban resilience. In the present research, land use changes in the middle Kashafrood watershed were investigated over a 20-year period (2003 to 2023). Then, the changes were predicted until 2033. Residential areas, with a significant increasing trend in the past 20 years, have accounted for the most changes.  A significant decrease in the area of agricultural land indicates the impact of the physical expansion of the urban area on decreasing agricultural land. Study of lithological units shows that landslide-prone structures such as the Mozduran, Chaman-Bid, and Upper Red structures, especially in the northern watershed, have a high potential for landslide occurrence. Based on the subsidence results, the highest subsidence values have occurred in the northwestern and the northeastern Mashhad. This is due to the presence of several factors, including groundwater overexploitation and the geological conditions of the region. The northwestern and northeastern areas of Mashhad, which showed the highest subsidence rates, are usually areas where groundwater overexploitation has occurred. These areas include urban and agricultural areas that 
require special water resource management. Finally, the present research has investigated the geomorphological impacts on the urban development and the challenges arising from natural hazards such as landslides and subsidence. The expansion of Mashhad is closely related to geomorphological landforms. Accur ate knowledge of these landforms and their impacts on urban development can help to improve the planning and management process. Geomorphological landforms, due to their multifaceted impacts on various factors such as location, urban growth pattern, infrastructure, and hazard management, are considered one of the fundamental aspects of urban planning. Mashhad, as one of the metropolises of Iran, is directly influenced by geomorphological elements such as highlands, slopes, alluvial fans, streams, riverbeds, and topography. The Binaloud Mountain in the south and Hazar-Masjed in the northeast of Mashhad, as natural barriers, have limited the physical expansion of the city. Construction on these slopes faces problems such as landslides and soil erosion. In contrast, plain surfaces with alluvial soils in the southern and northwestern parts have provided a favorable condition for urban and agricultural development. However, groundwater overexploitation in these areas has caused the occurrence of land subsidence, which is a serious challenge for sustainable development. Alluvial fan areas, due to their suitable soil permeability, have been employed as suitable conditions for the urban expansion, especially in the northwest and along the Binaloud pediment. The relationship between the expansion of Mashhad and the occurrence of landslide and land subsidence is an important challenge that requires serious attention. The physical expansion of Mashhad and its surroundings, especially in the northwest of the Mashhad plain, has increased the need for water resources. Expansion in steep areas, construction in steep and unstable areas without considering geological characteristics can lead to landslides, which cause great loss of life and property. The Hazar-Masjed and Binaloud Mountains present distinct geomorphological and lithological characteristics influencing landslide susceptibility. The western Binaloud Mountains, dominated by resistant rock units like the Mashhad phyllite, exhibit a moderate landslide potential. In general, lack of proper planning for urbanization management, human manipulation, destabilization of slopes, deforestation, and geological and lithological structures are among the causes of landslides in the Mashhad plain. Overall, a detailed study of the geomorphology of a region not only helps to better understand the natural dynamics and their effects on urban development, but can also lead to the development of efficient policies for urban management and reducing the risk of natural hazard. The results of this research, by improving comprehensive understanding of the environmental challenges, provide a pathway for urban planners and managers to increase urban resilience against these hazards.