Variability of monthly soil erosion by different land use/land covers of large Caspian Sea basin using G2 model
Document Type : Original Article
Authors
1
Former Ph.D. Student, Department of Watershed Management, Faculty of Natural Resources, Tarbiat Modares University, Noor, Iran
2
Department of Watershed Management , Faculty of Natural Resources, Tarbiat Modares University, Noor, Iran
3
Associate Professor, Department of Natural Resources, Faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili
10.22034/gmpj.2024.437820.1483
Abstract
Introduction
Soil erosion in Iran is one of the most important problems of drainage basins that can be mentioned as main barriers to the sustainable development of agriculture, geoscience, and natural resources. Therefore, soil erosion control is one of the most urgent environmental issues which need to identify in erosion-prone areas in the watersheds. In many watersheds, the role of land use in soil erosion is greater than of other factors. Knowing the contribution of different types of land use to soil erosion leads to managing land use and reducing the severity of soil erosion, and even increasing the income of the watershed stakeholders. Evaluation and identification of soil erosion in coastal regions are one of the most important measures for comprehensive coastal management. Therefore, the current research was carried out with the aim of estimating soil erosion in different temporal and spatial scales with the G2 model, according to the land use/land covers of the Caspian Sea basin.
Methodology
The northern region of Iran encompasses the Caspian Sea basin, which spans approximately 91,176 km2, equivalent to around 10% of the country’s total area. It is situated between latitudes 45°39'-35'N and longitudes 59°59'-44'E. With an average elevation of 1,195 m, the watershed exhibits significant variation, ranging from the highest point at Mount Damavand with an elevation of 5,699 m to the lowest point along the Caspian Sea coast at -28 m. The Caspian Sea basin is divided into seven primary basins and further subdivided into 108 sub-basins using the Strahler stream ordering method. In order to prepare soil erosion map in the study area, the input factors of G2 model were prepared in appropriate spatial and temporal scales using meteorological data, satellite images, application of GIS and RS. The G2 model combines five input erosion parameters in a multiplicative equation to produce month-time step maps and statistics of soil erosion. Ideally, a single layer suffices for S, T, and L factors, while a collection of 12 layers (one for each month) is required for the dynamic factors R and V. Also, the values of soil erosion were estimated for different types of land uses/covers in different time scales for the Caspian Sea basin.
Results and Discussion
The results showed that the average annual soil erosion for the study area is reported to be 11.24 t ha-1, the highest soil erosion rates observed in the West Azarbaijan, Mazandaran, North Khorasan, and East Azarbaijan provinces. On the other hand, the highest monthly soil erosion with the rates of 1.49, 1.48, 1.32, and 1.27 t ha-l were in November, October, April and May, and the lowest monthly soil erosion with the rates of 0.54 and 0.59 t ha-1 were in August and December, respectively. The highest amount of soil erosion occurred in autumn and spring compared to winter and summer. One of the reasons for the increase in soil erosion in the autumn season is the high intensity of rainstorms that occur in lands with little vegetation and in the spring season, may be due to the increase in rainfall and snow melting in this season and its effect on the increase of soil erodibility. Also, minimal soil erosion in summer and winter seasons can be caused by the decrease in the amount and intensity of rainfall or the absence of effective rainfall. In addition, it was found that with the increase of rainfall erosivity, soil erosion increased on a monthly time scale. The highest annual soil erosion with the rates of 16.87, 15.96, 11.51, and 11.22 t ha-1 were in rangeland, shrubland, barren lands and forest II, respectively. As a result, annual soil erosion values in the western, central, and eastern parts were estimated equal to 11.94, 13.47, and 10.53 t ha-1, respectively. Although the difference of soil erosion in monthly, seasonal and annual time scales in all different land use/land covers is significant at the 99% level, but it is not significant in a number of large land use/land covers in the Caspian Sea basin in the western-central, central-eastern and western-eastern parts.
Conclusion
According to the current research, 40.53% of the lands in the studied area have soil erosion of less than 1 t ha-1 yr-1, which are in the range of low erosion, because this amount of wastage is almost equal to the annual soil construction limit and is normal, and these areas do not need watershed operations and the risk of soil erosion is low. While about 18.73% of the land surface of the studied area, soil erosion exceeds 20 t ha-1 yr-1, and it is recommended that in these areas, in addition to biological operations, mechanical operations are also performed to reduce and control soil erosion. The results obtained from the present research provide managers and policymakers with information and appropriate decision-making bases for the management and sustainable use of soil and water resources.
Soil erosion in Iran is one of the most important problems of drainage basins that can be mentioned as main barriers to the sustainable development of agriculture, geoscience, and natural resources. Therefore, soil erosion control is one of the most urgent environmental issues which need to identify in erosion-prone areas in the watersheds. In many watersheds, the role of land use in soil erosion is greater than of other factors. Knowing the contribution of different types of land use to soil erosion leads to managing land use and reducing the severity of soil erosion, and even increasing the income of the watershed stakeholders. Evaluation and identification of soil erosion in coastal regions are one of the most important measures for comprehensive coastal management. Therefore, the current research was carried out with the aim of estimating soil erosion in different temporal and spatial scales with the G2 model, according to the land use/land covers of the Caspian Sea basin.
Methodology
The northern region of Iran encompasses the Caspian Sea basin, which spans approximately 91,176 km2, equivalent to around 10% of the country’s total area. It is situated between latitudes 45°39'-35'N and longitudes 59°59'-44'E. With an average elevation of 1,195 m, the watershed exhibits significant variation, ranging from the highest point at Mount Damavand with an elevation of 5,699 m to the lowest point along the Caspian Sea coast at -28 m. The Caspian Sea basin is divided into seven primary basins and further subdivided into 108 sub-basins using the Strahler stream ordering method. In order to prepare soil erosion map in the study area, the input factors of G2 model were prepared in appropriate spatial and temporal scales using meteorological data, satellite images, application of GIS and RS. The G2 model combines five input erosion parameters in a multiplicative equation to produce month-time step maps and statistics of soil erosion. Ideally, a single layer suffices for S, T, and L factors, while a collection of 12 layers (one for each month) is required for the dynamic factors R and V. Also, the values of soil erosion were estimated for different types of land uses/covers in different time scales for the Caspian Sea basin.
Results and Discussion
The results showed that the average annual soil erosion for the study area is reported to be 11.24 t ha-1, the highest soil erosion rates observed in the West Azarbaijan, Mazandaran, North Khorasan, and East Azarbaijan provinces. On the other hand, the highest monthly soil erosion with the rates of 1.49, 1.48, 1.32, and 1.27 t ha-l were in November, October, April and May, and the lowest monthly soil erosion with the rates of 0.54 and 0.59 t ha-1 were in August and December, respectively. The highest amount of soil erosion occurred in autumn and spring compared to winter and summer. One of the reasons for the increase in soil erosion in the autumn season is the high intensity of rainstorms that occur in lands with little vegetation and in the spring season, may be due to the increase in rainfall and snow melting in this season and its effect on the increase of soil erodibility. Also, minimal soil erosion in summer and winter seasons can be caused by the decrease in the amount and intensity of rainfall or the absence of effective rainfall. In addition, it was found that with the increase of rainfall erosivity, soil erosion increased on a monthly time scale. The highest annual soil erosion with the rates of 16.87, 15.96, 11.51, and 11.22 t ha-1 were in rangeland, shrubland, barren lands and forest II, respectively. As a result, annual soil erosion values in the western, central, and eastern parts were estimated equal to 11.94, 13.47, and 10.53 t ha-1, respectively. Although the difference of soil erosion in monthly, seasonal and annual time scales in all different land use/land covers is significant at the 99% level, but it is not significant in a number of large land use/land covers in the Caspian Sea basin in the western-central, central-eastern and western-eastern parts.
Conclusion
According to the current research, 40.53% of the lands in the studied area have soil erosion of less than 1 t ha-1 yr-1, which are in the range of low erosion, because this amount of wastage is almost equal to the annual soil construction limit and is normal, and these areas do not need watershed operations and the risk of soil erosion is low. While about 18.73% of the land surface of the studied area, soil erosion exceeds 20 t ha-1 yr-1, and it is recommended that in these areas, in addition to biological operations, mechanical operations are also performed to reduce and control soil erosion. The results obtained from the present research provide managers and policymakers with information and appropriate decision-making bases for the management and sustainable use of soil and water resources.
Keywords
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