Assessing the risks of developing Kabul settlements towards flood prone areas

Introduction
Flood is one of the most important environmental hazards. Floods have natural roots, but human activities play an important role in intensifying them. In fact, the development of residential areas towards the river and the destruction of vegetation have increased the likelihood of floods and intensification of damage. One of the areas that have faced an increasing population in recent years is the city of Kabul in Afghanistan. In fact, the political and social situation of Kabul has led to large population growth in recent years, so that the population of Kabul has doubled in the last 20 years. Parallel to the population growth, ‌ Kabul encountered significant physical development. The city of Kabul has a high potential of flood hazard due to being surrounded by a mountainous unit from the surrounding area, having a large catchment area upstream, and being located in a flood plain. Nevertheless, the physical development of Kabul city has been progressed during the recent years without regarding the geomorphological characteristics, so that many residential areas are located in high-risk areas, especially those adjacent to the Kabul River. Given the importance of the flood issue, it is necessary to identify the trend of physical development of residential areas in the Kabul urban basin and the increasing trend of these areas towards the flood-prone areas. Therefore, the current study aimed at the preparation of flood potential map of Kabul Basin and spatiotemporal development of the urban city in accordance with the flood-prone areas.
Materials and methods
In this research, in order to achieve the desired goals, Landsat satellite images, a digital model of 12.5 m altitude, geological maps, and climatic information of the region have been used as research data. Many software and models were used in the research include ArcGIS (to prepare maps), and IDRISI (to assess land-use change trends), as well as fuzzy logic-AHP (to identify areas prone of flood occurrence), and LCM model (to assess the trend of land-use change and the movement of residential areas towards areas prone to floods). This research has been done in several stages. In the first stage, in order to identify flood-prone areas, 8 parameters including slope, slope direction, height, distance from the river, precipitation, cumulative flow, lithology, and land use have been used. In the second stage, in order to prepare the land use map of the study area during the studied time periods, Landsat satellite images have been used. The Landsat satellite imagery used in the research is from the years 1990, 2000, 2010, and 2020. In the third stage, in order to analyze land-use changes, the LCM model is used, and then using this model, the trend of changes for 2050 is predicted.
Discussion and results
In this study, in order to identify areas prone to floods in the urban area of ​​Kabul, eight parameters have been used. Based on the results, many parts of the Kabul urban area are in the category of very high flood potential. According to the results, 369 square kilometers, equivalent to 26.8% of the area, are in the very low and low potential for floods, these areas mainly include high, steep, and far from the river. Also, 495 square kilometers, equivalent to 35.9% of the area are located on the floor with high and very high potential. These areas mainly include areas with low slope and height, as well as areas close to the river. The increasing population in the urban area of ​​Kabul has caused many parts of the residential areas to move to flood-prone areas in recent years. In order to evaluate the progress made, first the flood-prone areas of the study area have been identified (done in the previous section), after identifying the flood-prone areas, the residential areas located in this area during the study periods have been identified. The results indicate that many parts of the residential areas of the study area are on the floor with a very high potential for floods.
Conclusion
The results show that Kabul city has a high flood potential so that 495 square kilometers of the city limits and suburbs of Kabul have a high flood potential, which mainly includes the western, eastern, and southeastern parts of Kabul. These areas have a high flood potential due to low slope and height, cumulative flow, and proximity to the river. In this study, the trend of land-use change has also been evaluated. According to the results, the use of residential areas in 1990 had an area of ​​130.3 square kilometers, which in 2020 has increased to 1.205 square kilometers. The results of assessing the progress of residential areas towards flood-prone areas indicate that in 1990, 48.2 square kilometers of Kabul urban area was on the floor with a very high flood potential, which is 2000 to / 9. 58 square kilometers, ‌ increased to 80.9 square kilometers in 2010 and 84 square kilometers in 2020. In addition, the results of the assessment of the development trend of residential areas towards flood-prone areas indicate that the area of ​​these areas will increase to 96.1 square kilometers in 2050. The results show that Kabul city has a high flood potential and the development of residential areas has been done without considering this risk because a large part of the city area has been developed in flood-prone areas and this trend is ongoing.