Mapping agricultural activities and their temporal variations in the riverine ecosystem of the Brahmaputra River using geospatial techniques

Abstract

The study of spatiotemporal variations in agricultural activities in a riverine ecosystem is extremely important to understand the growth of crops during different seasons. The trend and pattern of change, help in understanding the suitability of different crops, cropping patterns practiced, and the scope of expanding agricultural activities for a better economy. In this study, the landuse land-cover (LULC) within the Brahmaputra River is categorized into different classes using unsupervised classification. The area under cropland and vegetation in the sandbars within the riverine is estimated, and the cropping pattern is analyzed on a decadal scale. Assessment of these classified maps is performed based on the overall accuracy and kappa statistics. Further, an agricultural portion in the mid sandbars of the river in the Lower Brahmaputra Valley (LBV) is considered to analyze the spatial cropping pattern as well as the expansion of cropland areas during different months in two different years. The temporal variation of the vegetation status of different classes is monitored using the Normalized Differential Vegetative Index (NDVI) and Normalized Differential Water Index (NDWI) for 2016 and 2019. Landsat MSS, Landsat 8 OLI and TIRS, IRS-1B LISS I, and IRS-P6 LISS III satellite images are used to understand the spatial and temporal variations as well as to evaluate the cropping pattern changes. On analyzing the trend of land cover changes during the period 1976–80, 1993–95, 2003–04, and 2008–11 from Sadiya to Dhubri, it is seen that the cropland area has decreased, vegetation area increased, and the sandbar area remained more or less unchanged. The average area of total sandbars within the Brahmaputra River is found to be 742002 Ha. Out of total area, 245395.75 Ha is found to be dry sandbars and 153148.23 Ha is covered under cropland and vegetation. On the contrary to the decreased cropland area, the monthly average percentage change was found to be + ~36% in the dominant agriculture sandbar between the years 2016 and 2019. We observed significant changes in the cropland as well as the conversion of barren sandbars into agricultural areas. The NDVI values obtained from the Landsat 8 OLI and TIRS satellite visibly indicated the change in the crop cultivation period as well as different phases of growth and shifting of cropping patterns. This study shows the potential and suitability of utilizing these vast sandbars of Brahmaputra River for various agricultural activities and improving the socio economic development of the people.