چکیده:
Desertification is a serious ecological, environmental, and socio-economic threat to the world, and there is an urgent need to develop rational methods for its evaluation at different spatio-temporal scales. This study aimed to address the main directions of desertification changes in Semnan County, Iran. Monthly precipitation was used to calculate a 12-month SPI (Standardized Precipitation Index) and the normalized difference vegetation index (NDVI) obtained by LandsatThematicMapper (TM) sensor of April month were used for the three years, viz. , 1987, 1998, and 2011. Five major categories were identified at level-I and they were subdivided into 11 categories including, 1. Residential areas, 2. Vegetation, 3. Bare and rocky areas, 4. Salt lands and 5. Sand areas. The results indicated that the reduction of the NDVI values was consistent with the changes in land use/land cover. This progress was taken place in some areas with the development of bare soil to salt land, and in some areas with the expansion of sand land, particularly from 1987 to 1998. The results indicated that the salt lands increased 348. 24 and 721. 57 square kilometers from 1987 to 1998 and from 1998 to 2011, respectively. The results revealed that desertification occurred at a rapid rate, especially towards the east and southeast directions in the study area. That was, towards the Dasht-e-Kavir and Damghan City. The results showed that besides using NDVI and SPI for drought monitoring, the meteorological variables such as temperature, sunshine hours and evaporation could improve the accuracy of interpretation of the results.
خلاصه ماشینی:
ir Desert 24-2 (2019) 217-227 Assessing Direction of desertification changes in an Arid Region (A Case study: Semnan County, Iran) S.
Other factors that affect desertification include wind and water erosion, rising runoff and flood risk, salinity of agricultural land and reducing soil fertility, reducing surface and ground water, threatening residential areas, industries, health threats to the inhabitants of the region and poverty and migration, (Rayegani et al.
Remote sensing data for natural resources management and food security has become in recent years a very powerful tool (Alavipanah, 2003; Kumar, and Shekhar, 2015; Fellah et al.
Other studies also reported that severe drought and desertification could reduce vegetation and soil by water and wind erosion resulting in reduction of agricultural productivity (Whiteford, 2002; Ranjpishe et al, 2018).
This study aimed to assess direction of changes in desertification and land degradation process in the Semnan County using remote sensing and meteorological indices.
1. Land use/land cover Change detection Table 4 shows the yearly SPI values and drought conditions from 1987 to 2012.
NDVI changes in Semnan County during 1987, 1990, 1998, 2001, 2009 and 2011 In addition to assess variations of precipitation, the other climate factors such as evaporation should be analyzed for desertification process (Kardavani, 2007; Amiraslani and Dragovich, 2012).
In addition to, our results showed that the normalized difference vegetation index (NDVI) obtained by remote sensing could widely used to monitor desertification change detection, which is in good agreement with those obtained from Li et al.
Assessment of land cover change and desertification using remote sensing technology in a local region of Mongolia.