Abstract

During late September, 2019 Bihar was struggling with severe flooding problem, which otherwise is marked as a period of flood recession due to withdrawal of south-east monsoons. The present study assess the flood situation using Sentinel-1 SAR images and complements the understanding about the flood event using long term (2000-18) multi-temporal space based flood sensitive proxy indicators like precipitation (GPM), soil moisture (AMSR-2), vegetation condition (MODIS) together with ground based river gauge (CWC) data. The study reveals that in 2019 during the 39^th week of the year (late September) the central and eastern parts of Bihar witnessed heavy precipitation (176 percent higher than average), leading to enhanced soil moisture build up (19 percent higher than average) and consequently triggering severe flooding. River Ganga was observed to be flowing above danger level for almost two weeks. Due to the prolonged submergence by floodwaters a significant drop was observed in the NDVI and EVI values of about 13.7 and 11.1 percent respectively from the normal. About 8.36 lakh ha area was observed to be inundated, impacting about 9.26 million population. Patna followed by Bhagalpur were the two worst affected districts with almost 30% and 36% of districts geographical area being flooded.

摘要

在2019年9月下旬，比哈尔邦（Bihar）陷入严重的洪灾问题，否则将被标记为由于东南季风的撤退而导致的洪灾衰退时期。本研究使用Sentinel-1 SAR图像评估洪水形势，并使用长期（2000-18）基于多时空的洪水敏感代理指标（如降水量（GPM），土壤湿度（AMSR-2））补充对洪水事件的理解），植被状况（MODIS）以及基于地面的河流水位（CWC）数据。研究显示，2019年第39^届在一年中的一周（9月下旬），比哈尔邦中部和东部地区出现了强降雨（比平均水平高176％），导致土壤水分积累增加（比平均水平高19％），从而引发了严重的洪灾。观察到恒河在危险水平以上流了将近两个星期。由于洪水长时间淹没，NDVI和EVI值分别比正常水平下降了约13.7％和11.1％。大约有836万万公顷的土地被淹，影响了约926万人。巴特那（Patna）和巴加布尔（Bhagalpur）之后是受灾最严重的两个地区，近30％和36％的地区地理区域被洪水淹没。