| چکیده انگلیسی مقاله |
Abstract
Flooding is a significant natural hazard that has increasingly threatened numerous Iranian cities, particularly in the western regions of Esan and Golestan in recent years. One notable event was the flood of April 2018, which resulted in substantial loss of life and financial damage across various western cities in Golestan Province. This research focused on monitoring the flooded areas in western Golestan and analyzing the environmental factors contributing to these events. The study utilized several key data sources, including Sentinel 1 and 2 radar images, MODIS, CHIRPS, Landsat 9 satellite imagery, and a 30-m digital elevation model. The primary research tools employed were Google Earth Engine, IDRISI, and ArcGIS. Initially, flood-affected areas were identified using Google Earth Engine followed by an analysis of their relationship with various environmental factors. Finally, flood-prone areas were delineated using the Weighted Linear Combination (WLC) model. The analysis of radar images indicated that in April 2018, significant flooding impacted urban and suburban areas, including Aqh Qhala, Siminshahr, and Gomishtappeh. The study revealed that altitude, slope, and vegetation density were the most influential environmental factors with correlation coefficients of 0.652, 0.619, and 0.543, respectively. Additionally, the WLC model identified the northern and western regions of the study area—comprising the urban and suburban areas of Gorgan, Aqh Qhala, Siminshahr, Gomishtappeh, Kordkoy, and Bandar Turkaman—as having high flood potential due to their low elevation, gentle slopes, sparse vegetation, and proximity to rivers.
Keywords: Flood, Environmental Factors, Google Earth Engine, West of Golestan Province.
Introduction
A flood is characterized by a sudden rise in river water levels or a rapid and often destructive flow of water. Flood risk affects populations worldwide, primarily because many people reside in areas prone to flooding. This widespread natural phenomenon poses significant challenges for regions vulnerable to floods, particularly as human activities and environmental interventions have intensified. In recent years, the increasing population and human activities have heightened the likelihood of floods, exacerbating the associated risks. According to the International Hazard Database, floods, alongside earthquakes and droughts, account for the highest rates of human and financial losses. Statistics from 2010 indicate that floods represent over 40% of natural disasters globally. Different regions exhibit varying potentials for flood risk based on geomorphological, hydroclimatic, and land cover factors. The northern regions of Iran, especially the eastern areas bordering the Caspian Sea, are particularly susceptible to flooding due to high rainfall and specific geomorphological conditions. This vulnerability has led to significant flood events in recent years, including the notable flood of April 2018. Given the importance of this issue, this research employed remote sensing methods to identify vulnerable areas in the western regions of Golestan Province and analyze the factors influencing flood occurrence. The study focused on parts of western Golestan Province and the eastern Caspian Sea selected for their flood potential. Geomorphologically, this area lies between the Alborz and Caspian Plain units. Its topography is predominantly low-lying with elevations below 50 m above sea level. Despite receiving an average annual rainfall of approximately 800 mm—less than that of the western Caspian coasts—the region's topography has facilitated the occurrence of numerous floods.
Materials & Methods
This research utilized several key datasets, including Sentinel 1 and 2 radar images, MODIS, CHIRPS, Landsat 9 satellite imagery, and a 30-m digital elevation model. The main tools employed in this study were Google Earth Engine (for generating maps of flooded areas and land cover), IDRISI (for running the Weighted Linear Combination (WLC) model), and ArcGIS (for map preparation). The research was conducted in several stages:
Identification of Flood-Affected Areas: In the first stage, flood-affected regions were identified using the Google Earth Engine.
Analysis of Environmental Factors: The second stage involved analyzing the influence of various environmental factors on flooding, including rainfall, distance from rivers, elevation, slope, vegetation density, and soil type. The selection of these parameters was informed by the specific conditions of the region and previous research. To create a map of regional rainfall, both Google Earth Engine and CHIRPS satellite images were utilized. Additionally, vegetation density maps were developed using Google Earth Engine, MODIS satellite imagery, and the NDVI index. For mapping elevation, slope, and distance from rivers, the SRTM 30-m digital elevation model was employed.
Vulnerability Assessment: In the third stage, the results and parameters from the previous stages—including precipitation, distance from rivers, elevation, slope, vegetation density, and soil type—were analyzed to identify areas vulnerable to flooding. Information layers for each parameter were prepared and standardized. These layers were then weighted based on the correlation coefficients obtained in the earlier analysis, which indicated the relationship between each parameter and areas prone to flooding. After applying the calculated weights to each layer, the information layers were imported into IDRISI software, where they were combined using the WLC model to generate the final map of flood-prone areas.
Research Findings
The research findings indicated significant insights into the flood events of April 2018 in Golestan Province, particularly regarding the environmental factors influencing flood risk.
Flood-Affected Areas
The analysis confirmed that substantial flooding occurred in urban and suburban areas, notably Aqh Qhala, Siminshahr, and Gomishtappeh. The data derived from Sentinel 1 and 2 radar images, along with other remote sensing tools, highlighted the extensive reach of the floodwaters.
Environmental Factors
The study evaluated the correlation between the flooded areas and several environmental parameters, yielding the following correlation coefficients: altitude (0.652), slope (0.619), vegetation density (0.543), rainfall (-0.517) (indicating an inverse relationship), and distance from river (0.437). These coefficients illustrated that lower altitudes and gentle slopes significantly contributed to the flooding. Additionally, areas with reduced vegetation density were particularly susceptible.
Soil Type Impact
The findings also identified that Aridisol soils were the most affected during the flood, suggesting a specific vulnerability linked to soil characteristics.
Flood Risk Mapping
Using the Weighted Linear Combination (WLC) model, flood-prone areas were delineated. The northern and western sectors of the study area characterized by low altitude, low slope, minimal vegetation, and proximity to rivers, were classified as having high flood potential.
Implications for Urban Planning
Given the high flood risk in western Golestan Province, the research underscored the necessity of integrating flood risk considerations into environmental planning and urban development strategies. The results advocate for heightened awareness and preparedness among local authorities and communities to mitigate future flood impacts.
Overall, the study provides a comprehensive assessment of the factors contributing to flooding and serves as a critical resource for future flood risk management in the region.
Discussion of Results & Conclusion
The findings indicated that during the floods of April 2018, a significant portion of the region, particularly the urban and suburban areas of Aqh Qhala, Siminshahr, and Gomishtappeh, experienced extensive flooding. After identifying the flooded areas, this research analyzed the relationships between these areas and various environmental factors, including average annual precipitation, distance from rivers, elevation, slope, vegetation density, and soil type. The correlation coefficient between flooded areas and average annual rainfall was found to be -0.517, suggesting an inverse relationship. In contrast, the correlation coefficients for vegetation density and distance from rivers were 0.543 and 0.437, respectively. The analysis revealed that low-slope and low-altitude areas were particularly susceptible to flooding with coefficients of 0.652 and 0.619 for elevation and slope, respectively, indicating a strong correlation. Additionally, flooding was most prevalent in areas with Aridisol soil types.
The western regions of Golestan Province demonstrated a high potential for flooding due to various environmental factors. This vulnerability had posed significant threats to residential areas and agricultural lands in recent years. The April 2018 flood exemplified this risk, affecting numerous cities in the region. The analysis of environmental factors revealed that altitude, slope, and vegetation density were the most influential with coefficients of 0.652, 0.619, and 0.543, respectively. Areas with low elevation, gentle slopes, and sparse vegetation experienced the highest levels of flooding. This research also produced a map indicating flood-prone areas based on the relationship between radar imagery and environmental parameters. The results highlighted that the northern and western regions of the study area, including urban and suburban areas of Gorgan, Aqh Qhala, Siminshahr, Gomishtappeh, Kordkoy, and Bandar Turkaman, were classified as having high flood potential due to their low altitude, gentle slopes, low vegetation density, and proximity to rivers. Given these findings, it is crucial to consider flood risks in environmental planning and urban development strategies. Special attention should be given to the flood-prone areas in the western regions of Golestan Province to mitigate future flooding impacts and enhance community resilience.
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