Mexico City: support for heritage management
The Mexicas built ancient city of Mexico over a lake. They designed an ingenious system that was both creative and practical, a clear demonstration of their highly developed technological and agricultural skills. Floating armatures of wood-logs were constructed on the lake and covered with layers of mud that accumulated to provide arable land on which to grow food. Both the ancient Mexica capital city and the Spanish historic centre were constructed over the lake.
Today, Mexico City is one of the most densely populated cities in the world. Water is in short supply and increasing amounts of groundwater are being extracted to meet the city’s needs, resulting in significant land subsidence problems. The historic centre of Mexico City was inscribed on the World Heritage List in 1987 but terrain subsidence is a major concern. Monitoring the historic centre to understand how it is moving is now essential for the preservation this World Heritage site’s buildings.
The German Aerospace Centre (DLR), a UNESCO space partner of the Open Initiative on the use of space technologies to support the World Heritage Convention, has been assisting UNESCO with this issue. DLR used its TerraSAR-X radar satellite, imaging the city from space between September 2009 and January 2010 and tracking changes, as shown here.
The areas of the Mexican capital where the greatest terrain movements were recorded by TerraSAR-X are shown in dark red. The green areas are those in which no changes were detected via the superposition of the satellite radar images between 20 September 2009 and 30 January 2010. The radar-satellite images show that even within this short time period, the ground moved as much as 10 cm in some places as a result of groundwater extraction. Two of Mexico City’s most famous landmarks, the Bellas Artes Opera House and the Metropolitan Cathedral of the Assumption of Mary, are sinking. DLR and UNESCO are assisting the Mexican conservation authorities by monitoring terrain movements in the area: space technologies assisting World Heritage sites.