Flood Mapping from Multi-Sensor EO Data for Near Real-Time Infrastructure Impact Assessment: Lessons Learned from the 2017 Spring Flood in Eastern Canada

Abstract

Spring 2017 flooding in the Canadian provinces of Ontario and Quebec was caused by a number of consecutive record-setting rain events combined with melting snow from early April to mid-May. The event significantly damaged residential infrastructure by flooding approximately 2500 Quebec residences in 146 municipalities, forcing mass evacuations and declaration of a state of emergency. The International Charter on Space and Major Disasters was activated shortly after on May 6, providing near-real time earth observation data from a range of sensors through Charter member agencies. Upon activation, the Emergency Geomatics Services (EGS) at the Canada Centre for Mapping and Earth Observation (CCMEO), Natural Resources Canada (NRCan), produced flood maps from Canada’s RADARSAT-2 and Charter satellite imagery to provide up-to-date emergency situational awareness. Previous flood extraction methods that relied on manual thresholding of single bands were deemed suboptimal to map open water in a timely and efficient manner from all data received through the Charter. In addition, previous methods ignored flooding beneath vegetation, which produced a large underestimation of flood extents on vegetated floodplains. Work that was ongoing in the previous year to develop reliable surface water extraction methods from multiple sensors for floodplain characterization were quickly adapted and put into operations during the activation, enabling rapid flood map production from RADARSAT-2, Sentinel-1 and TerraSar-X, among other sensors. This chapter describes the methodology and presents successes, challenges and lessons learned from the 2017 EGS activation for flooding in Ontario and Quebec, Canada.