عنوان مقاله [English]
Playas, in the arid and semiarid regions of Iran, due to recent climate changes and human activities such as extractions of mineral resources and irregularities in input water, have experienced new evolution which events lead to changes in the playa’s surface and forms. Sometimes human activities create changes in the natural environment that their firm conclusions can not be predicted. In the present investigation, superficial changes in the Hoze Soltan’s playa were examined some indexes as principal component analysis, normalized difference salinity index and temperature from the landsat satellite images over a period of 26 years from 1991 to 2016.
Materials and Methods
In the present study, three images from Landsat satellite 5, 7 and 8 related to 1991, 2000 and 2016 (i.e. a 26-year ) have been used to detect the changes in this playa. In order to determine the rate of resulted marginal changes, NDSI, PCA, and LST were calculate in the in a range of about 10 km from mentioned playa.
In order to calculate the surface temperature of the playas, No.6 thermal band image in 1991, band No.6-1 image in 2000 and band No.10 image in 2016 were used. In this playa, four-period-field observations during spring and Autumn of 2013 and Spring and Summer of 2016 were carried out; 25 samples of the various regional forms elicited.
Results and Discussion
Playa borders with PCA index in 1991, zone of 10.0; in 2000, zone of -0.06; and in 2016, zone of 0.07 were specified. Therefore, in all three images, these zones are made distinct from all PCA indexes which indicate the increase in playas’ square areas from 1991 to 2016 with a rate of 10.09 of square kilometers; this decline, furthermore, was around 33.59 square km more in 2000. As it was determined, the most changes in the playa borderlines were observed in the eastern regions. Reducing the surface area from 1991 to 2016 in the margin and it’s great retrogression from the east side is significant. The obtained results in the surface salinity level reveal that this surface has experienced about 1296 square meters’ decline in 1991 to 2000 and 1579.277 square km increase from 1991 to 2016. Due to the increase at the recorded temperature in the city of Ghom synoptic station, the maximum rate of the playas’ surface has increased, too; which, reveals the significant relationship in the temperature changes with the increase of salt layers accumulation in the playa’s surface in order to with increase in the salt layers accumulation, surface temperature decrease.
The findings of the present study demonstrate that the area square of the playa has diminished from 1991 to 2016; this decline seemed to have been more severe in the first ten years. Furthermore, while the most observed alterations in the playa areas have taken place in the eastern regions. In other words, the increase in the salinity areas during the years 1991 to 2016 has happened in the west and southwest margins of the playas and the retreat of this surface has occurred from the eastern side during 1991 to 2016. These records suggest that studied playas had spatial changes from the east to the west and southwest. These place changes have grown more sever in about 15 years.
The regression analyses between the salinity and temperature indexes exhibit that the increase in the salinity of the playas is accompanied by the decrease in the surface’ temperature as such that the least degree of surface temperature belongs to the zone of salt and mud and salt zone and the central and marginal regions of the playas. Moreover, these regions have the most density of salt layers and salinity index ratios in comparison to the entire surface of the region.
As regards the Hoze Soltan playa received the eastern part of it’s water from the mountains along the northern margin in the northern branches of the Shoor river’s alluvial fan, from the northern branches of Ghareh Chai’s alluvial fan; Moreover, this playa is surrounded by volcanic mountains from the southwest, west and northwest parts. It can be construed that given the decrease in the salinity of the playa surface from the east side, probably the flow of the incoming water reduces the salinity of the eastern sections of the playa. On the other hand, since the increase in the salt concentration is associated with decrease in the temperature, the place movement of these playas towards the southwest and west heights is justified.