Flood Monitoring and Assessment over the Himalayan River Catchment

Abstract

The Himalayan catchment area is highly prone to climate change with variability in rainfall and temperature affecting the lower elevation states to a greater extent. The present study is focused on rainfall variability over the Himalayan River catchment mainly in three states of India (Uttarakhand, Uttar Pradesh, Bihar) and Nepal from May to October 2021. To observe the rainfall intensity during the study period, the daily CHIRPS precipitation data were used in composites of 14 days. The highest rainfall intensities were observed in the Himalayan Mountain ranges of Nepal contributing to heavy runoff to the major streams originating from Nepal towards India, affecting many districts of north Bihar. The MODIS near-real-time (NRT) flood product was used to determine the flood inundation extent over the study period based on 14 days composite, which was later incorporated into different time ranges to derive the time till the water was stagnant in one place. Based on this, the districts were identified where the water was stagnant for less than 15 days, 15-30 days, 30-45 days, or more than 45 days. The districts in Bihar (Bhagalpur, Darbhanga, Katihar, Khagaria, Lakhisarai, Madhepura, Munger, Muzaffarpur, Patna, Samastipur, Saran, Vaishali) where the water stayed for more than 1 month were mostly confined to the proximities of the Ganga River channel. Using the Copernicus land use land cover information and floodwater duration of more than 30 days, the damage to cropland and the built-up area was assessed. The floodwater duration was very high in terms of these districts for which disaster preventive and mitigation measures need to be adopted along with risk reduction measures to minimize the disastrous impact of flooding.