Tehran - Iran's capital - is sinking dangerously, according to a new study by two geoscientists from the GFZ German Research Centre for Geosciences in Potsdam. About 10 per cent of the urban area of Tehran, as well as several villages and towns located in city's southwest are affected by this problem.
Tehran is the largest city of west Asia by population and is home to about 13 million people. According to scientists, Tehran has significantly lost its groundwater in the past few decades due to droughts, construction of dams, and steep increase in population. Lack of rainfall in periods of drought has also added to the lowering of groundwater level. Between 11984 and 2011, this level went down by 12 metres, according to scientists.
In the current study, Mahmud Haghshenas Haghighi and Mahdi Motagh from the GFZ German Research Centre for Geosciences examined high-resolution satellite images to investigate the level of subsidence of the Earth's surface across the Tehran region. These images were gathered by four satellite systems ALOS PALSAR, Envisat ASAR, Sentinel-1, and TerraSAR-X during 2003 to 2017.
The researchers used nine data sets from four satellites to analyse the responses of the Earth's surface to changes in groundwater levels. Sentinel-1 satellite was highly significant in the study as it provided images with a swath of 250 kilometres from the Tehran region every 12 days since 2016.
Researchers found that three areas in the capital sank by about 25 centimetres a year and several metres in total between 2003 and 2017. This subsidence rate is among the world's highest and has caused sudden appearance of sinkholes and giant cracks in some areas. The collapse has even spread to encompass Tehran's international airport.
According to scientists, the groundwater basins in some areas have been damaged irreversibly, and won't be able to store as much water in future as they used to. However, a proper plan for water management could help defuse the situation to some extent in future.
"Science and research could support Iranian administrations and governments to revise their water management policy for a sustainable development," said Motagh.
The researchers now plan to use Sentinel-1 data to measure the level of subsidence outside Tehran.
The findings of the study are published in journal Remote Sensing of Environment.
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