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SAR-Data-Based Flood Mapping and Regional Precipitation Trends Analysis
1, 2 , * 2
1  Research scholar
2  Department of Geoinformatics, School of Natural Resource Management, Central University of Jharkhand
Academic Editor: Riccardo Buccolieri


The variability in the river flow in relation to rainfall changes plays a pivotal role in understanding the occurrences of disaster in the Ganga-Brahmaputra basin. In the recent decade, findings are indicating an increase in flash floods and droughts due to the impacts of climate change. The present study is focused on the recent flood disaster in the Ganga-Brahmaputra basin mainly affecting the states of Bihar, and Assam in India during the months of July, August, September, and October 2022. SAR data-based flood inundation analysis was performed using the Google Earth Engine platform. The composite area for July to October under flood was estimated to be 11048.52 km2 for Assam and 4362.71 km2 for Bihar. Extensive area was inundated in Assam due to increased rainfall intensity during the monsoon season with values ranging from 384.92 to 476.07mm as compared to Bihar with 272.56 to 386mm. MODIS Land Cover Type Yearly Global dataset was used to calculate the impact of flood on agricultural area and urban areas which revealed that the highest impact was on Bihar with an area of 1563.14 km2, 463.81 km2 respectively, and Assam (161.19 km2, 51.91 km2). JRC Global Human Settlement Population Density layer was employed to evaluate the flood impacts which revealed that a total of 3.7 million of the population was affected. The highest impact in Bihar can be attributed to its vast population size and extensive settlements near riverbed areas whereas in Assam despite the higher inundated area the impact was less on agricultural land and urban area and more on other land cover classes. Following the same analysis, the trend of rainfall variability was also examined based on the Chirps precipitation data for the months of July to October from the year 1993-2022. The rainfall anomaly data was used to estimate the millimeter change per year. Bihar recorded the least precipitation variation in the month of August with major values ranging between 0.5 to -0.5mm year-1 however the month of October presents the highest variability over the past 30 years with an increase of more than 1.5mm year-1 after 2020 which has previously been non-significant. The major years when a prominent increase was observed are 1993, 1998, 2003-2005, and 2008. In recent years, the rainfall trend in Bihar is shifting towards the end of the monsoon with higher precipitation anomaly in October as compared to July. However, in Assam, the monsoon period has not recorded significant change in the anomaly from July to September with values falling between -0.5 to 1.0mm year-1. In October, the region recorded an increase of more than 1.0mm year-1 in the years 2000-2004, 2014, 2018, 2020, and 2022 with a maximum increase of 2.0mm year-1 in 2022. The trend analysis of precipitation change will provide an approach to identify the areas at risk with increasing or decreasing anomaly of 2mm year-1 in terms of flood and drought disasters which will provide necessary information regarding the reduction, mitigation, and management of disasters.

Keywords: SAR, flood inundation, impact assessment, rainfall variability.