Giriraj Amarnath International Water Management Institute (IWMI), Colombo, Sri Lanka

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Water for a food-secure world
BANGLADESH FLOOD RISK ATLAS
Giriraj Amarnath
International Water Management Institute (IWMI),
Colombo, Sri Lanka

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Water for a food-secure world
THE PROBLEM
• Floods – primary natural disasters
• Precipitation intensity and variability is projected
to increase – increasing risks of flooding
globally and in Asia
• Global economic losses from natural disasters -
over $165 billion annually
– More than current aid flow
– Floods take the lion share of this
• May rise to over $450 bill. by 2030

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Water for a food-secure world
FLOOD INUNDATION MAPS
• Inundation maps are needed for decision makers to better mitigate the
impacts of flooding and build more resilient communities
• An easily accessible flood maps will provide users more awareness of
the flood hazards in their local community.
• Currently, only a limited number of agencies have a flood risk mapping
interface.
• Our research program address mapping the extent of South Asia and
country level flood risk assessment for better flood management.

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Water for a food-secure world
FLOOD INUNDATION MAPPING ALGORITHM
• MODIS surface reflectance
• Global
• Temporal resolution : 8 days
• Spatial resolution – 500 m
• Period : 2000 – 2011
• Indices : EVI, NDWI, LSWI, NDSI
• DVEL (EVI-LSWI) was used to
discriminate between Water pixels
and Non–water pixels. If the
smoothed DVEL is less than 0.05 pixel
is assumed to be a Water pixel;
• Several procedure further
differentiate between permanent
water bodies and temporary Flood
pixels
• Applied in South Asia
• Being applied in South East Asia
MODIS 8-day composites of surface reflectance (MOD09A1)
Interim Map of inundated areas
Cloud
mask
NDSI NDVI EVI LSWI
Snow
mask
Permanent Water
mask
Vegetation + Crop
area
DEM
Global Wetland
Database
Validation and Accuracy
assessment
Final map of inundated areas (2000 – 2011)

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Water for a food-secure world
INDICES AND PRODUCTS

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Water for a food-secure world
ANNUAL FLOOD INUNDATION PATTERN (2000 – 2011)

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Water for a food-secure world
DURATION OF INUNDATION CYCLE

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Water for a food-secure world
SEASONAL INUNDATION PATTERN

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Water for a food-secure world
FLOOD RISK MAP
• Current flood mapping for the entire
Bangladesh has mapped areas at risk of
flooding.
• Provides a good foundation for efficient
flood-risk management.
• Useful input in drawing up flood-risk
management plans, for preventing flood
damages, in land use planning, for
providing information on floods, in rescue
operations in order to avoid flood risk.

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Water for a food-secure world
Time-series of flood inundation
pattern (2001 – 2011)
Yearly Flood Statistics
Monthly Flood Statistics
(2005 – 2011)

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Water for a food-secure world
BANGLADESH FLOOD RISK ATLAS
• EightDay_product
• Flood_Duration
• Flood_Monthly
• Flood_Occurence
• Flood_Seasonal
• Maps
• Statistics

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Water for a food-secure world
Thank You
Contact : a.giriraj@cgiar.org