Abstract
Critical information on a flood-affected area is needed in a short time frame to initiate rapid response operations and develop long-term flood management strategies. This study combined rainfall trend analysis using Asian Precipitation—Highly Resolved Observational Data Integration towards Evaluation of Water Resources (APHRODITE) gridded rainfall data with flood maps derived from Synthetic Aperture Radar (SAR) and multispectral satellite to arrive at holistic spatio-temporal patterns of floods in Sri Lanka. Advanced Land Observing Satellite Phased Array type L-band Synthetic Aperture Radar (ALOS PALSAR) data were used to map flood extents for emergency relief operations while eight-day Moderate Resolution Imaging Spectroradiometer (MODIS) surface reflectance data for the time period from 2001 to 2016 were used to map long term flood-affected areas. The inundation maps produced for rapid response were published within three hours upon the availability of satellite imagery in web platforms, with the aim of supporting a wide range of stakeholders in emergency response and flood relief operations. The aggregated time series of flood extents mapped using MODIS data were used to develop a flood occurrence map (2001–2016) for Sri Lanka. Flood hotpots identified using both optical and synthetic aperture average of 325 km2 for the years 2006–2015 and exceptional flooding in 2016 with inundation extent of approximately 1400 km2. The time series rainfall data explains increasing trend in the extreme rainfall indices with similar observation derived from satellite imagery. The results demonstrate the feasibility of using multi-sensor flood mapping approaches, which will aid Disaster Management Center (DMC) and other multi-lateral agencies involved in managing rapid response operations and preparing mitigation measures.
Highlights
Floods and droughts account for 78% of the people affected by all natural disasters in Sri Lanka (DMC, 2014) [1]
An overview of annual average rainfall trends for the whole of Sri Lanka deviating from the long-term mean for the period 1980–2007 estimated using APHRODITE rainfall data indicate a positive trend
This is consistent with the findings based on the number of flood events recorded in the Sri Lankan Disaster Inventory System—DesInventar (DMC, UNDP and UNDPRC 2009)
Summary
Floods and droughts account for 78% of the people affected by all natural disasters in Sri Lanka (DMC, 2014) [1]. Recurring floods caused by these monsoon rains are a common feature in Sri Lanka and such flooding has affected more than 7.8 million people since 2000 [1]. There have been 1438 deaths from approximately 1500 flood events in the past five decades in Sri Lanka. This value is comparatively lower than other South Asian countries such as India, Bangladesh and Pakistan [2,3]. High population density and concentrated economic activities in flood-prone areas further increases the vulnerability of Sri Lanka to adverse flood events
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