Increasing flood risk in the Indian Ganga Basin: A perspective from the night-time lights

Abstract. The changing climate, intense rainfall, and geomorphological conditions within the Ganga Basin have led to recurring flooding within the area in the recent past causing severe loss of life and property. The occurrence of such flooding events has increased the need to understand the complex interplay between flood hazards, exposure, vulnerability, and risk. This study delves into flood risk within India's Ganga Basin, focusing on the flood-inducing factors, vulnerability, and exposure through the application of the Analytical Hierarchy Process (AHP) which is a Multi-Criteria Decision Making (MCDM) model. The novelty of the work is using NASA's Black Marble Nighttime Lights as a proxy for human presence and economic activities as an alternative to conventional parameters for flood exposure such as population count, and household density. The study aims to capture the dynamic nature of flood risk, driven by hydro-geomorphic controls, expanding human activities and population growth, and variations in flood resilience. We show that there is a significant increase in flood risk trend in the eastern part of the basin, particularly areas in Bihar, eastern Madhya Pradesh, eastern Uttar Pradesh and the northern part of West Bengal, identifying high flood risk zones at the pixel or cell level. The novelty of the work lies in using night-time lights as a proxy for exposure within the basin, unlike the conventional population data. This study leverages the temporal availability of the data, enabling a real-time distribution of human activities at a large scale and with greater temporal resolution.

The accuracy of the flood risk maps is validated using the historical flood-impacted data from the EM-DAT and GDIS databases, showing a satisfactory model accuracy of approximately 70 %. The findings emphasise the role of increasing human exposure and changes in rainfall patterns as the key drivers for increasing flood risk over time. This research has significant implications for flood management, offering insights for developing risk mitigation strategies that transcend administrative boundaries by identifying areas of escalating flood risk.