Detecting the Effectiveness of Land-use Changes in the Spatial Distribution of Dust Concentration in Khuzestan Province using MODIS Sensor Products

Today, dust events in western and southwestern Iran have become one of the most important environmental hazards. The main purpose of this study is to reveal the relationship between land cover changes and dust distribution in Khuzestan province during the last two decades. In this regard, land cover data of MODIS sensor, Aerosol optical depth product of the same sensor aerosol and cross-analysis matrix technique were used to reveal the relationship among them. The results showed that firstly, the dominant coverings of Khuzestan province were generally pastures, barren lands, agricultural lands and urban areas. Analyzing the 20-year trend of these uses showed that rangelands, decreasing trend, agricultural and urban lands had an increasing trend and barren lands also had a relatively stable trend. However, the results of spatial analysis of AOD index showed that the mean and standard deviation of this index have reached from 0.35 ±09 in 2000 to 0.44 ± 0.04, in 2020 in the province during the last two decades. The important finding obtained by the cross-analysis matrix along with the analysis of periodic trends was that the use of medium to rich rangelands, which had not increased in the last two decades, the level of AOD in this use, with a slope of 6500 hectares per year, had a decreasing trend, while the agricultural land use on which the AOD index has had an increasing trend, with an annual slope of 18,700 hectares has had a significant increasing trend. Therefore, in general, it can be said that the increase in the area under cultivation of agricultural lands, and the lack of control of barren lands in the province, has led to the intensification of dust in the province over the past two decades

Land use research programs at a global scale have become central to international climate and environmental change research since the launch of land use and land cover (LULC) change project. LULC has two separate terminologies that are often used interchangeably. Land cover refers to the biophysical characteristics of earth surface, including the distribution of vegetation, water, soil, and other physical features of the land, although land use refers to the way in which land has been used by humans and their habitat, usually with an emphasis on the functional role of land for economic activities. Land use and land cover change is the conversion of different land use types which is the result of complex interactions between humans and the physical environment. LULCC is a major driver of global change and has a significant impact on ecosystem processes, biological cycles and biodiversity and also lead to some hazards such as dust storms. Today, dust events in western and southwestern Iran have become one of the most important environmental hazards. The western and southwestern regions of Iran, is faced with the phenomenon of dust and its problems significantly. In the west and southwest of Iran, there are desert areas such as the deserts of southern Iraq, Saudi Arabia and farther north in Africa, which causes frequent occurrence of dust with different intensities throughout the year in this part of the country. In addition to the mentioned deserts, the role of the local dust area is also very important in injecting dust into the air of the province. Among these, the role of extensive land use changes in Khuzestan province, including drying of wells and wetlands, degraded pastures with overgrazing, abandoned rain-feed agricultural, expansion of irrigated agricultural, are among the important changes that have coincided with the increase of dust. The main purpose of this study is to reveal the relationship between land cover changes and dust distribution in Khuzestan province of Iran during the last two decades (2000-2020).

In this study we used two types of data: the land cover data of MODIS sensor (MCD12Q1), and Aerosol optical depth product (AOD)(MOD04) during a 20-year period (2000-2020). The MCD12Q1 product of MODIS Terra+Aqua identifies 17 classes defined by the International Geosphere Biosphere Program (IGBP), including 11 natural vegetation classes, 3 human-altered classes, and 3 non-vegetated classes. The AOD data daily level-2 (MOD_04) data are produced at the spatial resolution of a 3 x 3 1-km (at nadir) pixel array. The aerosol product includes the "deep-blue" algorithm recently developed to get aerosol optical thickness over bright land areas. In this study, since the purpose was to investigate the status of spring and summer atmospheric aerosols in Khuzestan province, so MODIS sensor of satellite Terra (MOD04-3K) and Aqua (MYD04-3K) with a spatial resolution of 3 km for Khuzestan province were used out of 3650 frames of AOD product. In this study, the cross-analysis matrix technique in GIS was applied to reveal the relationship between AOD and land cover class. The temporal trend also was investigated using regression models during 2000-2020.

The results showed that firstly, the dominant coverings of Khuzestan province were generally pastures (Grassland), barren lands (Bare land), agricultural lands (Crop land) and urban areas (Built up class). Analysis of the 20-year trend of these uses showed that grasslands area has the decreasing trend, while the agricultural (cropland) and urban lands (built up area) had an increasing trend during last 2 decades. Barren lands also had a relatively stable trend, although the results of spatial analysis of Aerosols Optical Depth (AOD) index showed that the mean and standard deviation of this index in Khuzestan province during the last two decades, changed from 0.35 ±09 in 2000 to 0.44 ± 0.04, by 2020. An important result obtained by the cross-analysis matrix along with the analysis of periodic trends was that the use of medium to rich rangelands, which had not increased in the last two decades, the level of AOD in this use, with a slope of 6500 hectares per year, had a decreasing trend. However, the agricultural land use on which the AOD index has had an increasing trend, with an annual slope of 18,700 hectares has had a significant increasing trend.

In terms of foresight, it can be expected that if the situation of the two dust drivers in the region follows the same trajectory of the last 20 years, i.e. agricultural lands, especially irrigated lands, will have an increasing trend, and on the other hand, the province rangelands will trend. If they have a decrease, we should expect dust events with much more intensity and density in the province.