After almost a year of data collection the OpenDRI Sri Lanka team has finished mapping the exposure to flooding of every building in the Gampaha District’s Attanagalu Oya river basin. Gampaha District is a mixed urban and agricultural district located on the Western coast of Sri Lanka just north of Colombo. It’s an economically important, rapidly developing suburb of Colombo subject to annual flooding. Increased urbanization has elevated the levels of exposure to human, material, and financial damages from flooding even as increased climate variability from climate change has elevated the frequency of major flood events.
Following months of digitizing features by satellite imagery, our team and their counterparts in local government battled fierce sunlight, tropical humidity and torrential monsoon rains to successfully evaluate in person the exposure levels of 97,000 buildings in 192 local government units covering 200 square kilometers. They walked, drove on and mapped over 12,000 roads, paths and dirt tracks along the way, as well as helped local government officials revise their local administrative area boundaries with GIS software.
We checked all the resulting data for errors, revisited buildings to recollect when necessary and presented the resulting data to local government officials for final, official review and validation.
This was a massive effort and we’re keen to see the results used widely. After completing the mapping, the OpenDRI team held a training on OpenStreetMap and QGIS for Disaster Management Centre (DMC) technical staff from the national and district offices. These staff are now prepared to make maps with the exposure data we’ve created and create their own OpenStreetMap (exposure) data.
We’ve also hosted all the exposure, land use and roads data on the newly launched RiskInfo data sharing platform, another OpenDRI project output. Sri Lankan disaster authorities and development agencies now have access to a very high resolution exposure data set, one that can be used in risk management and risk sensitive planning alike Using RiskInfo GIS professionals who are not familiar with OpenStreetMap can easily download and reuse this Attanagalu Oya area data.
This blog marks the end of one OpenDRI project and the beginning of even larger works. In its next stage, OpenDRI Sri Lanka will evaluate the accuracy of the resulting data, refine the process accordingly and work with the Government of Sri Lanka to scale up this approach in other hazard prone areas. The DMC is now discussing how to scale up this approach with the Urban Development Authority , Survey Department and district authorities how they can scale up the OpenStreetMap-based approach to exposure mapping in the rest of the country, especially in flood prone areas. We’ll keep you posted as more details emerge, so watch this space.