Web-Based Mapping Solution for National Scale Flooding Analysis

Preventing the high impacts of extreme events requires the collaboration of various disciplines that do not spontaneously interact with each other. To facilitate fast and appropriate communication between people of different backgrounds and motivations, web-based tools and visualization become a major option. Using almost exclusively open-source libraries, we built a web-based mapping solution that has three objectives: integrate multiple data sources that are generally not displayed together, provide interactive visualization tools to help find information in the data sets, present new maps of surface water depth and flood risk on a national scale. Being a map-centric dashboard, we called it mapboard. The map contains meteorological data layers (rain, wind, temperature), geological data, land use and land surface data, and water cycle calculation results for all of Japan. Layer order and opacity are adjustable, allowing unique maps to be produced for each objective without the need for advanced geographic information system (GIS) knowledge. Data visualization is provided through interactive layers to display time series graphs and important values in a dashboard interface. We used this online tool to present the original results obtained with our hydrological model on a national scale covering all of Japan with a 500 meter grid. Using the GETFLOWS (GEneral-purpose Terrestrial fluid-FLOW Simulator) physical simulator, the model is capable of seamlessly integrating surface and underground flows to provide an accurate view of the entire water cycle of Japan. Among other applications, these results can be used as a basis for water balance analysis, flood and landslide forecasting studies, and refinement of the spatio-temporal model for advanced regional simulation. We have developed a global flood hazard map that focuses on predicting potential flood areas, locating safe areas, and estimating damage risks. Three-dimensional physical models that include rain/evaporation, surface runoff/infiltration and groundwater flow are not often used in flood forecasting because of the high calculations required, particularly at a national scale. Because it is designed to be accessible to the public and decision-makers, our online solution should be of great support in the event of dramatic situation such as the heavy floods that took place from June 28 to July 10, 2018 in the Shikoku and western Honshu regions of Japan, causing more than 200 casualties, more than 2 million people to evacuate and more than 6 billion US dollars in damages.