Monitoring Changes in Rice Cultivation Area Using Multi-Temporal Satellite Images (Case Study: Beiranshahr Region, Iran)

In arid and semi-arid regions, cultivating crops with high water demand can seriously threaten water resources. This research was conducted to investigate the expansion of rice cultivation areas from 2013 to 2021 in this region. For this purpose, using Landsat 8 and Sentinel 1 satellite images, the changes in rice cultivation in this area were determined. After radiometric and atmospheric corrections, the Normalized Difference Vegetation Index (NDVI) was calculated. The vegetation area in hectares was obtained using the pixel size of the images. Finally, the change in vegetation area with time was plotted graphically. For more certainty, the cultivated area in August 2021 was also determined with radar images. After performing the preprocess corrections (thermal noise removal, calibration, terrain flattering, multilink, speckle filter and terrain correction), a suitable RGB image was created. Then sampling was done on different classes of land. The final land cover map was prepared using a random forest algorithm. In order to estimate the trend in the time series of area change, the MannKendall test was used and the nonparametric Sen’s method was used to determine the slope of a linear trend. The results showed that the area under rice cultivation has increased from 2,564 hectares in 2013 to 4,771 hectares in 2021. The results of the Mann-Kendall test showed that a positive increasing trend exists in the data series. Investigating the underground water level showed that the depth of the water in some parts of the region has reached 10 meters, while in the past, the depth of the underground water in this region was less than 2 meters. These findings show that increasing rice planting in this region can endanger the region’s water resources, and in the long term, the region will face serious challenges. Therefore, it is recommended to limit rice cultivation in the region and cultivate crops with less water demand instead.