UNOSAT Emergency Mapping: Thailand hit by floods (2021)
Discover satellite derived maps and analysis created by the United Nations Satellite Centre (UNOSAT) during the Thailand flood activation.
Flood activation
Thailand is known to be a flood-prone country, with heavy rains and flooding occurring during the monsoon season every year. In it’s geographical context, the large network of shallow rivers, allows for very easy overflowing on the river banks.
During the 2021 monsoon season, Tropical Storm Dianmu followed by Tropical Storm Kompasu brought heavy rains in the northern, central and eastern parts of the country, as well as strong winds, causing floods and landslides.
Map shows the path of Tropical Storm Kompasu in September , 2021. Source: Global Disaster Alert and Coordination system - GDACs
UNOSAT Rapid Mapping Activation
On the 27 September 2021, the United Nations Satellite Centre (UNOSAT) emergency mapping service was activated following a request from the Geo-Informatics and Space Technology Development Agency, Thailand (GISTDA), the United Nations Economic and Social Commission for Asia and the Pacific (ESCAP), and the United Nations Office for the Coordination of Humanitarian Affairs (UNOCHA).
The widespread flooding event occurred for over a month, affecting 32 of the country’s 76 provinces, according to the Thailand Department of Disaster Prevention and Mitigation. Due to the large areas flooded, in a short time span, access to satellite imagery and geospatial analysis was necessary to provide analysis and evidence to inform emergency response and recovery.
Image: Inundated agricultural areas in Suphan Buri province, Source: Facebook Basnadee
The UNOSAT team was able to undertake satellite-derived assessments and analysis, focusing on the flood extent as it changed over time.
The maps and data produced, highlight flooded infrastructure, such as roads, as well as the exposure of the population at the community level in different priority areas, both of which were necessary for the coordination of the emergency response.
Maps and products were frequently released throughout the activation on both an interactive dashboard , as well as static maps, data, and geospatial files which were made available for direct download.
Background image: AI Flood detected waters using Sentinel-1 imagery on Thailand basemap (ESRI), analysis by UNOSAT.
Monitoring the flood
Persistent rain brought more flooding to the central and northeastern region, between late September and early November 2021. Analysis was undertaken using both manual and automated methods, using an automated analysis with machine learning and AI techniques.
Start of the flood: End of September 2021
The map shows Satellite-detected surface waters in Northern (29 September) and Central (1-2 October) parts of Thailand as observed from a Sentinel-1 image, source: ESA.
Progression early October 2021
Satellite-detected surface waters in Northern (29 September, 5, 9, 15 October) and Central (1-2, 10 October) parts of Thailand as observed from Sentinel-1 images, source: ESA.
Progression end of October, and early November 2021
Satellite-detected surface waters in Northern (29 September, 5, 9, 15, 17 October, 8 November) and Central (1-2, 10, 20 October, 1 November) parts of Thailand as observed from a Sentinel-1 image, source: ESA.
Impact of the flood
The flood progression shows the wide extent of the floodwaters across Thailand, during September, October, and November 2021. The flooding not only put millions of people and livelihoods at risk but also impacted small cities/ towns, key infrastructure, cultural sites, and farmland/ agricultural regions.
Sites of interest
Many different sites and locations across Thailand were impacted by the floods, a selection of sites are listed below with accompanying imagery.
Lam Chiang Krai Dam, Non Thai District
Many small cities and townships were affected by the floods, including multiple settlements partially immersed in flood waters. In the central region Non Sung and Non Thai districts had areas that had fully affected settlements.
Imagery location and Nakhon Ratchasima outlined in blue.
The Lam Chiang Krai Dam, in the Non Thai District, was broken and overflowed causing inundation to houses during the flooding.
Left image: Sentinel-2 , 1 April 2021. Right image: Sentinel-2, 28 September 2021. Copyright: Copernicus Sentinel Data [2021] Source: ESA
Major roads and rail network
Still in the central area of the country, in the Non Sung District, infrastructures such as major roads and railways were also affected. Some of these can be seen on the interactive map, with satellite imagery showing the flood extent.
Imagery location and Nakhon Ratchasima outlined in blue.
Satellite imagery: Pleiades, 29 September 2021. Copyright: CNES (2021), distribution Airbus D&S Source: Airbus DS. Analysis and production: United Nations Satellite Centre (UNOSAT)
Cultural heritage sites
Multiple cultural buildings and temples were flooded in the Phra Nakhon Si Ayutthaya Province.
Phra Nakhon Si Ayutthaya Province outlined in blue.
Wat Chula Manee in the North Western region and Wat Satue, pictured here, in the North Eastern region both came underwater during the flooding.
Thailand's ancient royal city of Ayutthaya flooded by tropical storm Dianmu
Background image from Reuters , 6 October 2021.
Summary
The large amount of satellite images acquired, the complete derived analysis and the numerous data produced were all shared in a timely manner with the concerned partners including GISTDA, who was able to produce a comprehensive analysis of the situation. All products were made available to the end-users online via the dashboard, updated daily, for digestible, evidence-based information. The objective information released was also frequently disseminated to local authorities and the population by the UN country office.
Beyond informing decision-making during this activation, the data now in the hands of disaster management authorities will be available to improve emergency preparedness and response, capacity development and training of local experts, as well as to support and inform climate resilience-building policies.
Testimony by Gita Sabharwal, UN Resident Coordinator, Thailand - Emergency Mapping Activation
