Evaluation of land use changes and its effects on soil erosion in the basin upstream of Yamchi Dam in Ardabil, using ARAS multi-criteria decision algorithm and modern remote sensing methods

Introduction

One of the environmental hazards and ecological crises that the world is facing today is the phenomenon of land use change (Mousavi et al., 2015) and awareness of land use changes over a period of time for planners and managers. It is very important (Tachizuka et al., 2002). On the other hand, soil is one of the most important natural resources that plays an important role in agricultural production and food security (Moghadasi et al., 1397) that during the erosion process, soil particles are separated from their main bed and with the help of a transfer agent to They are transported to another place (Maslink et al., 2017; Research et al., 2011). Surface soil erosion reduces the depth, reduces the moisture capacity and the loss of organic matter and nutrients and thus reduces soil fertility (Parvizi et al., 1399).



Methodology

The research is an applied research and the result is the study of land use change and analysis of soil erosion potential in the basin upstream of Yamchi Dam in Ardabil province. This study is based on the use of remote sensing methods to achieve land use change over a period of 21 years and the use of ARAS multi-criteria analysis method in GIS environment to zoning the potential of soil erodibility of the basin. It is above the Yamchi Dam. ENVI, Ecognition, Arc GIS, Idrisi and Excel softwares have been used for image processing and data analysis. In order to investigate the risk of erosion in the data collection stage, first according to the natural and human conditions of the region, slope factors, lithology, land use, rainfall, distance from the communication road, distance from waterway and soil, as effective factors in Basin soil erosion was identified. In the next step, information layers related to each factor were prepared in the GIS environment. The information layers of communication routes and waterway network were prepared and measured using the map of communication lines and rivers of Ardabil province. The slope layer was prepared using a digital model of 12.5 m altitude, Alos satellite, Palsar sensor, obtained from the site (vertex.daac.asf.alaska.edu). To extract a layer of information related to lithology (resistance of rocks), from the geological map of Ardabil province; Used at a scale of 1: 100000. The precipitation map of the basin was drawn according to the data of meteorological and rainfall stations using the precipitation gradient equation (P: 0.227H-85.04).



Results and Discussion

It can be said that in the erosion map of both study periods, mainly high-risk and high-risk areas in agricultural uses, poor and medium rangelands, man-made areas and barren lands are located. According to the erosion zoning maps in the study area, in 2000, the area of high-risk and high-risk floors was 74.35 and 206.51 square kilometers, the amount of these risk classes in 2021, respectively; Increased by 79.40 and 219.98 square kilometers. The reason for the increase in areas with the risk of erosion can be considered in the reduction of good pastures, medium pastures and mountainous lands and their conversion into agricultural areas, poor pastures and man-made areas. Saffari et al. (1397), Asghari Saraskanrud et al. (1398), Miyahi et al. (1400), Santos et al. (2017), Kiden et al. (2019), Kojo et al. (2020), Lee et al. (2021), Also, increasing the area of agricultural lands, barren lands and residential areas and in contrast to reducing pastures have been mentioned as the main reasons for increasing the potential risk of soil erosion.

At the level of the study basin, by the villagers of the region, most rangeland lands; They have changed the use of agricultural lands, especially low-loss land. Although rainfed fields play an important role in increasing agricultural production and food supply, but land use change due to the impact on vegetation and soil surface erosion, intensifies soil loss and surface runoff and thus soil quality It affects. This change of use, if it is combined with not paying attention to land capability and observing the correct principles of tillage, leads to the production of surface runoff and thus intensifies erosion, which ultimately results in reduced fertility and reduced yields. According to the combination of slope and land use map, most of the sloping meadows in the basin, which are the focus of erosion, are scattered in the middle half and to some extent in the southern parts on slopes of 15 to 35%. Given that most agricultural lands in particular; The meadows of the region are located on sloping slopes, so plowing in the direction of the slope, especially during heavy rains, leads to soil erosion. Thus, in parallel plowing, the water from rainfall flows more easily in the cultivation furrows and is removed from the arable land and as a result, water and soil loss increase. On the other hand, uncontrolled harvesting of forage from pastures to feed livestock in the cold season and early grazing in spring has reduced the amount of pastures and intensified runoff with the onset of the rainy season, and this affects the morphology of rivers. It also has a direct effect and leads to a change in bed behavior.



Conclusion

Knowing the ratio of uses and how it changes over time is one of the most important things in planning and policy making. In addition, soil erosion can be considered as one of the biggest obstacles to achieving sustainable development in agriculture and the use of natural resources. For this reason, the phenomenon of erosion has been considered globally. It can be added that land use change is one of the important factors in causing soil erosion. Therefore, in the present study, land use change and its role in soil erosion using telemetry techniques and ARAS multi-criteria analysis for the two periods of 2000 and 2021, has been investigated.