Flood damage from extreme rainfall and typhoons keeps recurring, but until now it has been hard to compare at a glance which of Gyeonggi-do's 31 cities and counties is relatively more at risk. To diagnose relative risk across cities and counties, Gyeonggi-do calculated a flood risk index, reflecting both inundation from river overflow (external flooding) and inundation from inadequate urban stormwater drainage (urban flooding), by city/county and by year (2016-2024). The closer the index is to 1, the higher the relative likelihood of flood damage in that city or county when extreme rainfall or a typhoon occurs.

The index is a risk assessment result derived by combining four categories, how intensely rain fell (hazard); how many buildings, people, farmland, and roads are exposed to inundation risk (exposure); how many vulnerability-increasing factors are present, such as aging buildings, dependent population, and underpasses (vulnerability); and the level of preparedness in terms of disaster prevention facilities and budgets (mitigation capacity), across 13 sub-indicators.

To improve the accuracy of the assessment, frequency-based flood maps matching the actual scale of rainfall in each region that year were selectively applied, and only assets actually exposed to inundation risk, such as buildings, population, farmland, and roads, were selected and reflected in the index calculation. In addition, optimal weights were applied to minimize the discrepancy between the index ranking and the heavy-rain and typhoon damage ranking in the Disaster Yearbook, verifying consistency with actual damage records.

The city/county-level flood risk index and its sub-indicator indices can be used as reference data to compare relative flood risk levels across regions and support policy decisions related to flood control projects and disaster prevention budget allocation. However, this index does not directly predict damage amounts for a specific area; rather, it is an indicator for comparing and diagnosing relative and potential flood risk levels across cities and counties.

While the city/county-level index shows 'which city or county is more at risk', this map shows 'which area within that city or county is more at risk', at the 100 m × 100 m grid level. Flood risk was assessed by year (2016-2024) for areas at risk of inundation from river overflow (external flooding) and inadequate urban stormwater drainage (urban flooding), and the calculated index is provided in 10 grades. The higher the grade, the relatively higher the likelihood of flood damage in that area.

The index is a risk assessment result derived by combining three categories, how deep and widespread inundation could be (hazard); how many buildings, people, farmland, and roads are exposed to inundation risk (exposure); and how many vulnerability-increasing factors are present, such as aging buildings, dependent population, and underpasses (vulnerability), across 11 sub-indicators.

To improve the accuracy of the assessment, frequency-based flood maps matching the actual scale of rainfall in each region that year were selectively applied, and only assets directly exposed to inundation risk, such as buildings, population, farmland, and roads, were selected and reflected in the index calculation.

Using the 100 m grid-level index, it is possible to precisely identify high-risk areas with a dense concentration of exposed assets, even within cities and counties already assessed as having high flood risk. Because risk is assessed at the 100 m × 100 m grid level, it can also be used for localized disaster response, review of river improvement sections, and spatially tailored policymaking at the project-district level, such as for urban development projects.

However, this index does not directly predict damage amounts for a specific location; rather, it is an indicator for comparing and diagnosing relative and potential flood risk levels across areas.

Information on flood-vulnerable facilities in Gyeonggi-do was constructed by integrating attribute data from building registration records and LiDAR-based high-resolution spatial data. Spatial information from LiDAR, including building location, height, and area, was combined with registration attributes—use, floors, structure, construction year—to identify facilities vulnerable to extreme rainfall, such as basements or old buildings. This data can support practical policy-making, including disaster response planning and prioritization of disaster prevention facilities.

The Flood Risk Map visualizes the extent and depth of inundation caused by embankment failure or by water overtopping the embankment under extreme flood conditions that exceed the design standard (design frequency) the river embankment was built to withstand. It covers national and local rivers and provides maps for various scenarios by flood frequency. The Urban Flood Map assumes that stormwater drainage facilities exceed capacity or malfunction, and shows the extent and depth (five levels) of inundation that could occur in urban areas. Both maps are produced and distributed by the Ministry of Climate, Energy and Environment, and are used in disaster management policy, including disaster risk area designation, disaster prevention facility planning, and early warning system development.

A flood trace map is spatial data recording the extent and depth of flood damage from typhoons or heavy rainfall based on field surveys and measurements. In accordance with the Natural Disaster Countermeasures Act, local government heads prepare it within six months of the damage, and it is provided by the Ministry of the Interior and Safety. The map includes information on flood extent, depth, and duration, and is used to identify frequently flooded areas, designate disaster risk zones, establish recovery plans, and determine priorities for installing disaster prevention facilities.