Evaluating and Modeling Temporal-Spatial Changes of Land Use in the Expansion of Desertification Intensity in the Arid Regions of Northeast Iran (Sarakhs)

Increasing land-use changes have increased the need for managers and experts in land resources to understand how changes and developments have occurred as well as possible future changes for good and efficient policymaking and decision-making (Parker et al., 2003; Akbari et al., 2019). Today, land use change is important in terms of environmental change and has got the attention of scientists and decision makers (Mas et al., 2014).The increasing destruction of natural resources in many parts of the world is a serious threat to humanity. Therefore, desertification, which is one of the manifestations of this destruction, is currently a problem in many countries, including developing countries (Parvaneh, 2009). At present, remote sensing technology with the highest speed and accuracy is a suitable tool for assessing land use changes in order to monitor desertification (Hashemi-Nasab et al., 2018; Davari et al., 2018). Different land use models have been designed and used by researchers to predict land use changes in several studies such asDavolbit and Morari (2012) in Sudan, Lamchin et al. (2016) in Mongolia, Halabian et al. (2016) in Iran, Isfahan, using land use modeling, assessing and predicting desertification changes.Studies show that in recent years, land cover around the world has undergone many changes that can severely affect the environment and natural resources. Given that land degradation leads to desertification, this issue intensifies the importance of studying land cover changes, considering the strategic importance of Sarakhs region. In the present study, the temporal-spatial changes of land use in intensity of desertification have been investigated and modeled using satellite images.2. Study AreaThe study area of ​​Sarakhs is a small part of the great Gharakhum basin which is located in Sarakhs city. The border of the region is in the western and southwestern part of Bazangan and Shurluq mountains, in the northern part is the Iran-Turkmenistan political border and in the eastern part of Tajan river. Geographically, the ferns range is located at 60 degrees 15 minutes to 61 degrees 10 minutes east longitude and 35 degrees 50 minutes 36 degrees 40 minutes north latitude. This area is naturally prone to desert expansion, which is exacerbated by its proximity to the Qaraqoom desert, creating a dry and cold climate. Wind erosion is more common in arid climates, where soil productivity intensifies drying conditions. Sarakhs region suffers from critical desertification conditions due to arid climate, low rainfall, unfavorable soil, land use change and increased wind erosion. The study area, as the epicenter of wind erosion crisis, has created environmental problems. Therefore, due to acute environmental and human problems and strategic location, Sarakhs was selected as the study area.

In this study, Landsat TM and ETM+ sensors were used to study land use dynamics. Geometric, radiometric and atmospheric corrections were performed on the images. Satellite imagery from 2000 to 2015 was monitored to prepare the land use map and examine its changes over 15 years. In this study, Landsat satellite imagery classification maps were first prepared using the maximum likelihood method for the mentioned years. Finally, the user map for different years was prepared. The LCM Land Change Modeler was used to model land use change in 2030. Modeling in this model was done in three stages. In the first stage the influential variables were selected and introduced to the model and the role of each of them according to the Kramer coefficients was determined. In the second stage, the potential transfer map was prepared based on the effective variables and land use maps of the previous periods and in the third stage, the future land use map was prepared. The validity and reliability of the modeling and classification maps are based on the estimation of the kappa coefficient and overall accuracy. Common validation maps of classification lands and changes model prediction maps were used for validation. In this way, the predicted map of the model was compared with the land use map produced by the supervised method and obtained by calculating the standard kappa coefficient, position accuracy status and pixel quantities of each class.

Map of land use classes of Sarakhs area in six classes of water level, agricultural lands, poor, and bay rangelands, medium and rich rangelands, wind deposits and residential areas and Landsat satellite imagery classification for the years under study were prepared. To determine the percentages of land use changes in the study period, each of the classes obtained in different years was individually placed on the sum of the classes obtained the following year, and then the number of changes of each of these uses was calculated in 2015. To import the variables into the land change modeler, it is necessary to map the variables. Altitude variables, distance from residential areas, distance from the road, distance from river and distance from agricultural land were selected as input variables of the model. It is possible to estimate the correlation of each variable with the existing land use and its ability to predict land use changes by calculating the Kramer coefficient. After revealing land use changes over the years 2000 to 2015, the number of changes in each transfer was predicted using the Markov Chain and the total land-use change map in the LCM model for 2030. To validate the power of the LCM model to produce land use maps for 2030, the 2000 and 2005 maps were first used to predict the 2015 map. To make this prediction, the change probability matrix and the probability area matrix of changes were prepared and based on defined sub-models and change probability maps, the 2015 land use map was prepared. Comparison of the model predicted map with the land use map prepared by the supervised method and calculation of standard kappa coefficient, accuracy condition for position and quantity of pixels of each class were obtained. The 2015 ground truth map was then compared with the simulated map of the land-change modeler. The accuracy of the model was evaluated based on the Kappa index. The error matrix results showed that the kappa coefficient of variation in the land change model is 0.85. Using the multilayer Preston neural network approach, the user change map for 2030 was obtained. According to the results, the process of reducing the average and rich rangelands and agricultural lands continues. The extent of wind deposits will also increase, covering about 17% of the area in 2030.

In the present study, land use changes in the north east of the country over the three-time periods 2005 to 2015 were investigated using Landsat satellite imagery and the ability to predict land-use changes based on the LCM modeling approach. Comparative results of land use maps in the three mentioned periods show the level of change in all land uses. The degradation of medium and rich rangelands in the third period was higher than the degradation of the second and first periods, indicating more severe degradation in the 2015–2010 period. One of the reasons for most of the degradation of rich rangeland during this period is the reduction of rainfall, drought and surplus livestock in recent years. The most varied land use changes over the years can be attributed to a decrease of about 3 percent in medium and rich rangelands, an increase of three percent in poor and barren rangelands and an increase of about one percent in agricultural lands. The total area of ​​the sand has increased by more than 1% over the whole period. The decrease in rangeland and the increase in waste and agricultural land indicate the inappropriate use of these lands for agricultural purposes. Damage to rangelands, increased levels of agricultural land with the degradation of land, use of land outside their ability and potential have led to increased desertification. During this period, the area of ​​residential areas grew by about 0.2%. The results of predicting changes over the next 11 years using the LCM modeler show that if the current trend continues in the region, the development of sand dunes and increased rangeland destruction will continue. In the 2030 horizon, sandy zones will cover about 17 percent of the area, and the extent of the desert and poor rangelands will be about 60 percent.