Posted by feww on June 24, 2016
Eastern portion of Beijing sinking at a rate greater than 100 mm/year: Study
Now you see it, now you don’t! China’s capital Beijing could disappear in a gigantic sinkhole.
Beijing’s massive subsidence, which has been occurring since at least 1935, is caused by the overexploitation or mining of groundwater. About 60% of the water supply comes from groundwater, and the rest from surface water.
Beijing used about 3.6 billion cubic meters (m³) of water in 2010, compared to renewable fresh water resources of about 3 billion m³. [The consumption may have risen by about 14% over the past five years.]
Article: Imaging Land Subsidence Induced by Groundwater Extraction in Beijing (China) Using Satellite Radar Interferometry
Beijing is one of the most water-stressed cities in the world. Due to over-exploitation of groundwater, the Beijing region has been suffering from land subsidence since 1935. In this study, the Small Baseline InSAR technique has been employed to process Envisat ASAR images acquired between 2003 and 2010 and TerraSAR-X stripmap images collected from 2010 to 2011 to investigate land subsidence in the Beijing region. The maximum subsidence is seen in the eastern part of Beijing with a rate greater than 100 mm/year. Comparisons between InSAR and GPS derived subsidence rates show an RMS difference of 2.94 mm/year with a mean of 2.41 ± 1.84 mm/year. In addition, a high correlation was observed between InSAR subsidence rate maps derived from two different datasets (i.e., Envisat and TerraSAR-X). These demonstrate once again that InSAR is a powerful tool for monitoring land subsidence. InSAR derived subsidence rate maps have allowed for a comprehensive spatio-temporal analysis to identify the main triggering factors of land subsidence. Some interesting relationships in terms of land subsidence were found with groundwater level, active faults, accumulated soft soil thickness and different aquifer types. Furthermore, a relationship with the distances to pumping wells was also recognized in this work.
Chen M, Tomás R, Li Z, Motagh M, Li T, Hu L, Gong H, Li X, Yu J, Gong X. Imaging Land Subsidence Induced by Groundwater Extraction in Beijing (China) Using Satellite Radar Interferometry. Remote Sensing. 2016; 8(6):468.
Groundwater from aquifers is a main source for drinking, irrigation and industrial use for much of the world’s population. Globally, an estimated 4 billion people depend on groundwater for drinking, but the water is running out!
Groundwater cannot be replenished from rainfall, and in most cases it takes tens of thousands of years to restore naturally.
According to the International Water Management Institute, about 1,000 cubic kilometers of groundwater are withdrawn each year, which is wholly unsustainable!
- Total water on Earth: 1.4 x 10^18 m³
- Water in the oceans: About 97.5% of the total
- Volume of Fresh water: Approximately 35 x 10^15 m³ of the earth’s total water. About 0.3% of the freshwater is held in rivers, lakes, and reservoirs and the remainder is stored in glaciers, permanent snow, and groundwater aquifers.
- Water contained in the earth’s atmosphere: about 13 x 10^12 m³
- Water removed from the earth’s surface via evaporation: about 577 x 10^12 m³ each year (only 14% of the water evaporation is from land).
- Total annual precipitation falling on land: about 115 x 10^12 m³ (20% of total evaporation – the 6% surplus water returns to the oceans via rivers.)
- Total freshwater on Earth stored as groundwater: Approximately 11 x 10^15 m³ (30% of all freshwater).
- Water collected in lakes and rivers: about 110 x 10^12 m³ is held as groundwater (one hundredth of the total groundwater reserves)
- Aquifers contribution to human water consumption: an estimated 30% [?] of all of the water used throughout the world.
- Natural recharge rate for the aquifers: from 0.01% to 3% per year.
- Estimated overdraft of global groundwater: about 200 x 10^9 m³ or (twice the average recharge rate!)
World cities and agricultural lands that are situated above aquifers and groundwater reserves are slowly but permanently sinking into the ground, as the water is pumped out at phenomenal rates.
In China, at least 46 cities are sinking into the ground due to the excessive pumping of groundwater. In Shanghai excessive groundwater pumping contributes to 70 percent of surface subsidence (the remaining 30 percent is thought to be due to the weight of buildings).