Digging the Flood Map - Which Map to Trust

Why are the flooding maps of the local government and the central government markedly different?
Support, the government, and reporters know the problem only after reporting on the report
Can Korea prepare for the era of the climate crisis?

In the last article, the YTN Data Lab pointed out that flooding maps, which should be a safe guide for citizens during the climate crisis, are operating in confusion. (Related article: Flood risk semi-underground housing, tracking with data ② / Too different 'Inundation map'...What should I believe?) This time, let's take a step further and dig a little more into the backside of the disaster information management system, which we didn't know or have turned away from, focusing on the flooding map.

According to the Natural Disaster Countermeasures Act, local governments are obligated to produce an inundation trace map when flood damage occurs, and the Ministry of Public Administration and Security is required to operate a related map integration system.

Currently, the "disaster map" released by the government and local governments varies from inundation trace map, urban inundation map, river inundation map, coastal inundation forecast map, landslide risk map, earthquake occurrence site, and heat distribution map. In addition, the disaster information map includes evacuation routes and evacuation sites in the event of a flood. Examples include the Ministry of Public Administration and Security's life safety guidance that can be found on the Internet, Seoul Safety Nuri in Seoul, and the disaster guidance of the city's integrated information system in Busan.

Life Safety Map Inundation Traces Capture Screen

Most of these data contain spatial information that is deeply related to weather disasters in the era of climate change. Among them, it is necessary to first refer to the inundation trace map that indicates areas that have been submerged by extreme rain, that is, areas that have already been damaged in the past and have the potential to be damaged in the future. Information about which buildings in which areas are poorly drained, low-lying, or lack of dimensional facilities and how inundated they are, or "traces of climate disasters," is important data for finding ways to minimize future damage.

But what about the reality? To put it bluntly, the inundation traces released by the government and some local government sites were dualized. The contents were not different, and it was so different that I wondered if it was a completely different flood map. What's more serious is that the central government wasn't aware of the local system until the reporter informed the agency. To make matters worse, there seems to be a lack of historical data and records to find out why this happened.

Let's go back to the cases of Incheon and Seoul covered by YTN in the broadcast report.

Screenshot screens of web maps of habitual flooding areas in Incheon

First, if you search Incheon's habitual flooding area on the Internet, it will lead to a data map released by Incheon Metropolitan City. If you click on the shortcut, you can check the open data of Incheon Metropolitan City. Like all other data maps, there are two types of flooding maps. There is a web map that is displayed on the screen for easy reference, and there is a map data in the form of a data file that can be downloaded for analysis from the Geographic Information System GIS tool, a professional data analysis tool. All of them are open to ordinary citizens, and downloadable data files are essential data, especially when practitioners and experts establish disaster prevention measures or urban planning. The city of Incheon is offering both. If you click the word 'map view', you can connect to the web map screen, and check the habitual flooding areas in downtown Incheon, which were created as of 2017. These areas have already been reported through media reports, and the Incheon Metropolitan City's official document, "Incheon Metropolitan City Natural Disaster Reduction Comprehensive Plan," confirmed that these areas are classified as domestic disaster history districts.

However, if you look at the signs of flooding in the disaster map corner of the life safety map site operated by the Ministry of Public Administration and Security, you can see at a glance that most of the habitual flooding areas disclosed by Incheon City are missing. The reporter compared and analyzed the GIS file of the inundation trace of the life safety map acquired by requesting the Ministry of Public Administration and Security through an official letter and the GIS file released by Incheon City. When the Incheon Metropolitan Government calculated the area classified as an "invasive flooding area," it was 1.3 times the size of Yeouido, Seoul.But 99.8% of them, so to speak, almost all of the "hyperinvasive infiltration areas" were omitted from the life safety map. What's more, it's hard to understand is that the habitually flooded area is almost completely inundated by the inundation trace map, which marks areas that have been submerged more than once.

Seoul Open Data Plaza Capture Screen

The Seoul Metropolitan Government is releasing the inundation traces of 11 years in the form of a web map from 2010 to 2022 through a site called Seoul Safety Nuri. Furthermore, the Seoul Metropolitan Government's open data plaza site allows all 11 flood traces to be downloaded in the form of a public data map that can be analyzed.

As expected, I compared it with the file of the Ministry of Public Administration and Security's inundation traces. Even with the naked eye, you can see that there is a difference between the two inundation traces. According to the GIS analysis, 60% of the flooded areas (based on the area) displayed in the Seoul public data flood trace file were omitted from the flood trace map of the life safety map. Mainly, there was a big difference in the flooded areas in 2010 and 2011. Why did this gap arise? Which one should I trust?

<The mystery of the submerged map>

During the
coverage process, the flooding map managers of the Seoul Metropolitan Government, Incheon City, and the Ministry of Public Administration and Security confessed that they were not aware of this in common. It also acknowledged that the big problem was that the maps released by local governments and the maps of the Ministry of Public Administration and Security were divided separately.

The Ministry of Public Administration and Security, which operates a life safety map site, said, "The problem is that the inundation trace itself was released by collecting map files submitted by each local government, and that the local government disclosed data that the source was unknown and that they were wrong."

Incheon Metropolitan City gave an unexpected answer to the process of making the map file of the habitual flooding area. The official in charge of producing the map file at the time in 2017 said he had moved from the department, and only heard that "there were many maps I made at the time, and I couldn't remember well because it was old." There is no record of what kind of map the cartographer has left. However, it was not possible to hear the exact information through the mouth of the person who made the Incheon Metropolitan City flood map. However, through the document of Incheon City's 'Comprehensive Plan for Reducing Natural Disasters', we were able to confirm that it matched the flooded areas in downtown Incheon. "It is a map that has been comprehensively judged by reviewing the flooding history and disaster prevention performance goals," he explained. However, it was difficult to hear a quick answer as to why most of the "invasive flood zones" were missing from the flood trace map submitted to the Ministry of Public Administration and Security.

A Seoul Metropolitan Government official explained the background of the big difference between the data map and the life safety map posted by the city because the 2010 and 2011 flood maps were not reliable and only reliable. Reproduced maps were posted on the web maps of Seoul Safety Nuri and the Ministry of Public Administration and Security's Living Safety Maps, but public data map files on public data portals and open data plaza sites explained that existing maps were uploaded.

So how did you sort out which one is correct? In addition to the inundation area, data attribute values such as the inundation time, inundation depth, and inundation area should be reflected in the data map file, but such detailed information is missing, so it is not accurate. In other words, a more reliable flood trace map would have been re-produced by combining the inundation damage information on the National Disaster Safety Management System (internal system of the government and local governments) entered in 2015 and the inundation trace map originally produced in 2010 and 2011. However, we still could not hear a definite answer as to how the internal database was created at the time in 2015 and why the inundation traces were made "inaccurate" in 2010 and 2011. It also raised the issue that among the flooded areas that were removed during the reproduction process, areas that were likely to have actually been flooded were included, but only the answer was that there was no room for correction or supplementation in the absence of evidence.
Under the
Natural Disaster Countermeasures Act, the 'Guidelines on Disaster Map Preparation Standards' defines 'inundation' when urban and rural residential and commercial industrial complexes are submerged in water more than 30 cm, causing significant inconvenience.Of course, according to the judgment of the head of the local government, the scope of flooding could be set wider, so different standards could be applied. The Ministry of Public Administration and Security explained that from this year, all inundation damage will be included in the inundation trace map regardless of the depth of the water, but it is highly likely that the past inundation traces were written on a different basis for each local government. In addition, how much professional manpower and budget needed to produce an "accurate" flood trace is also an important variable.

Both the Ministry of the Interior and Safety and the Seoul Metropolitan Government explain that the inundation trace of the life safety map submitted to the central government is more credible. However, there are still more than a few things that are difficult to understand.

The 'Guidelines on Disaster Map Preparation Standards' stipulate that the inundation trace represents the largest inundation trace in the past as inundation information. Can we believe that the inundation trace map on the life safety map represents the largest inundation trace in the past? The digital map, which was released separately by Incheon and Seoul as public data because some attribute information was missing, includes a number of flooded areas where local residents vividly remembered the flooding or reported in the media. We cannot rule out the possibility that the domain is somewhat overestimated, but it is hard to deny the whole information.

It is also a change in recent years that local governments have created and preserved flood traces on digital maps and the Ministry of Public Administration and Security has begun to build and operate such disaster maps as an integrated management system. However, there are still not a few loose corners everywhere. In addition to the Incheon and Seoul cases confirmed by the reporter, there are many points to supplement the flooding traces of other local governments. Twenty years ago, a series of articles titled "Country Without Records" was reported in the domestic media that accused the poor management of national records. If the reality is that the inundation map, which is key information in the era of climate disasters, was poorly produced and the evidence to reconfirm the exact situation at the time of flooding has disappeared, Korea is still a country without a record. Are we prepared to properly respond to climate change?

#Data Journalism #ClimateDisaster #ClimateCrisis #PublicData

Article and Data Analysis: YTN Data Lab Ham Hyeong-gun Reporter
Graphic Design: Jeong Hye-ryeon

utilized data sources and references list

1. Life safety map of the Ministry of Public Administration and Security Shp file National Inundation trace map (2002-2023)

2. Seoul Inundation Trail Shp File (2010, 2011, 2012, 2013, 2014, 2016, 2017, 2018, 2019, 2020, 2022)
Public Data Portal, Seoul Open Data Plaza

3. Shp file of Incheon Metropolitan City's habitual flooding zone (as of 2017) Public data portal. Open Data for Incheon Metropolitan City

4.2019 Incheon Metropolitan City Comprehensive Plan for Natural Disaster Reduction document

5. Natural Disaster Countermeasures Act
Guidelines on criteria for preparing disaster maps
(National Legal Information Center)