Nightlights as a tool to study flood exposure and vulnerability for the 2022 Indus River flood.

Flooding is one of the most devastating of natural disasters, occurring at varying spatial scales and leading to human and resource loss. Where the extent of flooding is large, satellite-derived data such as the NASA-derived DMSP, VIIRS, or the Black Marble nightlights data provide a useful approach for flood extent, flood exposure, and vulnerability. The recent floods in August 2022 on the Indus River, Pakistan is an example of a high-magnitude flood event. According to Pakistan’s National Disaster Management Authority (NDMA), around 33 million people were affected by the floods, and 8 million people were displaced.

To quantify exposure to flooding, we explore the use of nightlight data in determining flood vulnerability and human impact. We first associated lit pixels of the NASA DMSP nightlights data with channel pattern type and the proximity to the river in the Indus basin to provide an understanding of the influence of landscape parameters on human presence. Based on the hypothesis of preferential human presence near the river of the basin, we show that nightlight distribution is enhanced by 26% within the 0 to 5 km proximity of the river relative to the basin as a whole. This finding shows how human presence is concentrated in close proximity to the Indus River and its key tributaries.

To quantify the impact of the August 2022 floods we use NASA’s monthly and daily Black Marble night light data. We compare published flood extents with spatial and temporal variations in nightlights over similar areas to examine the impact of flooding on human presence. We use this to quantify the impact of the floods as measured in terms of the percentage of affected or reduced nightlight pixels and to estimate differential recovery time periods of the floodplain versus the non-floodplain area of the Indus river. The results will be compared with the population and demographics statistics of the area to provide information about flood exposure and vulnerability of different socio-economic groups within the flood plains. Our findings have the potential to aid improvement in our understanding of flood risk assessment and vulnerability and provide a framework for policymakers to assess flood vulnerability and impact at a basin scale.