India - PALSAR remote sensing enables accurate flood-mapping of Bihar State

By Ed Hill

As a result of increasing conversion of forests to agricultural and pastural land in the middle hills of Nepal, run-off into the rivers has increased, especially into the Koshi, which flows through a narrow gorge as it enters Bihar state. This, along with increasing settlement in the floodplains of the rivers, has significantly increased the frequency and severity of flooding in Bihar, which accounts for almost half of India’s average annual flood losses.

Although the state government has built about 3,000km (1,875mi) of embankments along the river banks, the flow of the river has grown such that the embankments have failed in almost every flood since 1979, with the most serious floods occurring in 2008, when one of the embankments failed and the river changed its course to an earlier channel.

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Fortunately, new district-level mapping of flood-prone areas was achieved in Bihar in August 2016 with the help of the International Centre for Integrated Mountain Development (ICIMOD). ICIMOD Koshi Basin Programme (KBP) coordinator and hydrology expert, Dr Shahriar Wahid, noted that mapping and monitoring floods can be highly challenging using satellite data, especially as floodwaters are rising, since the majority of satellite remote-sensing is optical, and land images are obscured by rain-bearing clouds.