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| Titel |
A surprise result of geothermal numerical simulation - Persistent drawdown of ground water table may reduce local climate warming rate |
| VerfasserIn |
Fengling Yin, Yaolin Shi, Huai Zhang |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250090423
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| Publikation (Nr.) |
 EGU/EGU2014-4659.pdf |
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| Zusammenfassung |
| Due to persistent groundwater over-exploitation since the 1970s, groundwater level
has been found significantly declined in a large area of more than 70,000 km2 in
Beijing, Tianjing and Hebei Provinces in North China. Consequently, a series of
geo-environmental problems have emerged and drawn widely public attentions,
such as land subsidence, groundwater contamination, sea water invasion, etc. We
found that decline of water table can result in significant reduction in geothermal
heat flux density, and this effect has never been discussed in literatures. Thermal
properties, such as thermal conductivity, specific heat, are different for layers of water
saturated sediment beneath the water table and layers of dry sediments above the water
table. When the water table declines, due to the variation of thermal properties,
transcend changes of underground geotherm occurs. Our numerical simulation indicates
that surface heat flow density may reduce 40%, about 25mW/m2 in ground water
drawdown zone in North China after more than 40 years over-exploitation, and
the surface heat flow density cannot return to normal state for hundreds of years
even if the water table does not decline any more from now on. The amount of
reduction of heat flow density is small, but it can last for long period of hundreds
of years, and cover a large area of 70,000 km2, its effect on climate may not be
negligible. It is estimated that this reduction of surface heat flow may reduce an air
column temperature 0.08°/a if it is adiabatic with surroundings, while the actual air
temperature warming rate is only 0.03°/a in the depress zone and 0.05C/a outside the
depression zone in North China. Meteorological subsurface temperature (up to 3.2m
depth) records show similar trend. Although air temperatures are influenced by many
factors, but the decline of surface heat flow density should be one of the factors to be
studied. We suggest that more attention should be paid to this effect, and systematic
monitoring of geotherm at tens to hundred meters depth should be carried out. |
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