India – Palsar Remote Sensing Enables Accurate Flood-mapping of Bihar State

In a floodlist article of 25 August, 2016, it was reported that the Bihar State disaster management department in India had estimated that the current floods had affected almost 3 million people.

The state of Bihar is bordered to the north by the mountainous country of Nepal, with several rivers running through the state; among them the Ganga, Sone, Punpun, Falgu, Karmanasa, Durgavati, Koshi, Gandak and the Ghaghara, to name a few. Bihar receives heavy rainfall from June through to October, and 85% of its land is under cultivation.

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.

In order to improve its disaster risk reduction plans and to prepare effective responses to flooding, the Bihar State Disaster Management Authority (BSDMA) requires reliable information regarding the extent of the event. This especially relates to the mapping and monitoring of flood-affected villages.

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.

However, using the PALSAR-2 (Phased Array-type L-band Synthetic Aperture Radar, version 2) sensor aboard the ALOS-2 satellite (Advanced Land Observation Satellite No. 2), launched in 2014, KBP in collaboration the Japan Aerospace Exploration Agency (JAXA) was able to generate near real-time flood information and damage assessments, since PALSAR has the capability to map flooding in all kinds of weather and at all times of the day.

An ALOS PALSAR image indicates areas inundated with water. The colour red signifies flooding while black marks normal water bodies and/or water flow. (ALOS PALSAR/JAXA)
An ALOS PALSAR image indicates areas inundated with water. The colour red signifies flooding while black marks normal water bodies and/or water flow. (ALOS PALSAR/JAXA)

With the support of the Australian Government, KBP was able to generate district-level flood inundation maps for Bihar’s thirty-three districts, and an online flood application system. During the August 2016 flooding, ICIMOD and JAXA were able to quickly provide an estimate of the flooded areas. Including agricultural, grassland, barren area, built-up area and fishponds, it found that floodwaters had engulfed 18,755 sq. km, affecting ninety-four percent of the state’s agricultural land.

“Bihar Inter Agency Group (BIAG) members, namely international non-governmental organisations and United Nations agencies, are currently assessing the impact of floods in Bihar in the affected districts, and naturally this flood map would be extremely helpful for them,” said Asif Shahab, Project Officer, Environment and Climate Change, BSDMA.

Flood maps illustrating village-level inundation could support BSDMA in several of its community-level risk reduction activities, he said, adding that the maps would be useful to the State’s disaster management department which is involved in search-and-rescue operations, distributes relief supplies and manages flood-relief camps.

Map showing flooded areas in Saharsa district, Bihar, as of 01 August 2016. Image: ICIMOD
Map showing flooded areas in Saharsa district, Bihar, as of 01 August 2016. Image: ICIMOD

Flood summary

Last updated: September 12, 2016
Event
Bihar, India, July to September 2016
Date
July 15, 2016
Type
Inland flood, River flood
Cause
Extreme rainfall, Long-term rainfall
Department of Disaster Management Bihar report as of 18 July, 31 villages in Araria and Supaul had been flooded. By 27 July, over 1,500 villages had been flooded in the eight affected districts: Kishanganj (543), Purnea (478), Araria (292), Supaul (106), Katihar (177), Bhagalpur (8), Madhepura (48) and Darbhanga (9).On 28 July, villages in the districts of Saharasa (7) and Gopaiganj (15) were also affected.By 02 August, the districts of Saharsa, Gopalganj, East Champaran, Muzafferpur had also been affected.From 05 August, the districts of Saran and West Champaran were also affected.After a short respite where many were able to return to their homes, further flooding struck from 19 August, with the worst affected districts being Patna, Bhagalpur, Vaishali, Buxar, Bhojpur, Sonepur, Saran, Begusarai, Samastipur, Lakhisarai, Khagaria, Munger, Nalanda and Katihar.

Locations

A - Kishanganj
B - Purnea
C - Araria
D - Supaul
E - Katihar
F - Bhagalpur
G - Madhepura
H - Darbhanga
I - Saharsa
J - Gopalganj
K - East Champaran
L - Muzafferpur
M - West Champaran
N - Saran
O - Patna

Magnitude

River level
33.2 metres
Mahananda River at Jhawa, Katihar, - July 28 to July 28, 2016
The highest recorded level there is 33.52 from August 1987

Damages

Affected
1.7 million
July 15 to July 28, 2016
As of 27 July, over 1,500 villages had been flooded in the eight affected districts: Kishanganj (543), Purnea (478), Araria (292), Supaul (106), Katihar (177), Bhagalpur (8), Madhepura (48) and Darbhanga (9).By 02 August, 2,200 villages had been affected, including villages in the districts of Saharsa, Gopalganj, East Champaran and Muzafferpur.By 07 August, 2,391 villages were affected, including parts of West Champaran and Saran districts.
Fatalities
228 people
July 15 to September 12, 2016
Evacuated
641,707
July 12 to August 8, 2016
Evacuated
715,158
August 19 to August 30, 2016
After a short break from the rain where many were able to return to their homes, further flooding struck from 19 August.
Affected
3.753 million
August 19 to August 23, 2016
Further flooding struck from 19 August, mostly affecting Patna, Vaishali, Buxar, Bhojpur, Saran, Begusarai, Samastipur, Lakhisarai, Khagaria, Munger and Katihar.