Investigation of soil salinity changes related to landforms of desert areas in the northern Isfahan province

Soil salinity in recent decades due to increasing population in the world and especially in developing countries, has been considered as an environmental hazard that is a very serious threat to the lives of residents of areas prone to desertification, especially in arid and semi-arid regions. This issue has intensified the process of desertification in these areas due to the decrease of precipitation and the gradual increase of temperature. However, soil salinity, like other environmental hazards, has no immediate effects (Metternich and Zink, 2013); but because of its consequences in human life, it is highly studied in today's world and is considered as a serious risk (Yu et al., 2010). At the same time, salinity is considered as one of the 7 factors of desertification and is 80% of the cause of desertification (Karam et al., 2019). Since the expansion of soil salinity and the destruction of fields and rangelands in the north of Isfahan province is one of the environmental hazards in this geographical area, the present study aims to identify and investigate this unfortunate phenomenon in this area using It deals with satellite numerical data as one of the important factors of land degradation. It may provide a platform for planning de-desertification and soil management in the region to achieve sustainable development and improve environmental conditions.

Soil salinity is one of the most important processes that limit plant growth and causes the spread of desertification and land degradation in arid and semi-arid regions. Distribution of soil salinity in different landforms and its changes over time and prediction of salinity patterns have a significant contribution in environmental management in arid and semi-arid and desert areas. The purpose of this study is to investigate the changes of soil salinity phenomena in desert landforms in the north of Isfahan province using Landsat satellite images, TM5 and OLI-TIRS sensors in the period 1987- 2020. For this purpose, 200 images were extracted in the 27 warm months of the year from June 1 to the end of August during this period. After the necessary preprocessing and mosaic and the composition of the band of the 4 images covering the image covering the study area, the salinity indices of NDSI, BI, SI-1 and SI-2 were evaluated and the relevant maps were drawn. The topographic position index and classification of landforms based on TPI were also examined.

The results showed that the trend of changes in salinity index increases from mountainous areas to low lands. The status of salinity indices in landforms extracted from TPI showed that the unit of mountains and heights have the lowest and the unit of flat plains (playa, mud and clay pan) have the highest values. The difference between these two landform units in all indicators is about 0.2. Investigation of salinity indices in the elevation tints shows that these indices decrease severely with elevation, up to the threshold of 1400 m, then the rate of the change decreases. Salinity indices decrease more with increasing slope; up to a slope of 15°, then the rate of change get gentler up to a slope of 65°. Salinity indices showed three temporal phases of change that the third phase has continued from 2008 - 2020 (12 years) with an increasing trend. The predicted maps (for the year 2030) illustrated that the southern region of Daq-E-Sorkh, including the pediments between Kashan and Ardestan, is in a critical situation, which requires the attention of environmental and natural resources managers and engineers to this issue.

The results showed that the trend of changes in salinity index increases from mountainous areas to low lands. The status of salinity indices in landforms extracted from TPI showed that the unit of mountains and heights have the lowest and the unit of flat plains (playa, mud and clay pan) have the highest values. The difference between these two landform units in all indicators is about 0.2. Investigation of salinity indices in the elevation tints shows that these indices decrease severely with elevation, up to the threshold of 1400 m, then the rate of the change decreases. Salinity indices decrease more with increasing slope; up to a slope of 15°, then the rate of change get gentler up to a slope of 65°. Salinity indices showed four temporal phases of change that the fourth phase has continued from 2014 - 2020 (6 years) with an increasing trend. The predicted maps (for the year 2030) illustrated that the southern region of Daq-E-Sorkh, including the pediments between Kashan and Ardestan, is in a critical situation, which requires the attention of environmental and natural resources managers and engineers to this issue.