BEIJING, May 3 (Xinhua) -- Groundwater in some parts of China is decreasing, according to new research on the subject.

Researchers used data from satellite gravity surveys, hydrological models and on-the-spot observations to study changes of groundwater storage in three aquifers in China.

They found water table in the North China Plain had declined by six to eight billion tons each year since 2002, due to dry weather and over exploitation for a long period.

Groundwater reserves in Northeast China have significant annual fluctuations. In the Liao River Basin, groundwater depleted rapidly from 2005 to 2009, with an annual loss of about five billion tons. Since 2010, however, increased rainfall has allowed reserves to gradually rise again.

Groundwater plays a critical role in the global water cycle. Some cities such as Beijing and Tianjin have limited exploitation to raise their water table.

The researchers are from the Institute of Geodesy and Geophysics under the Chinese Academy of Sciences, Capital Normal University and Ohio State University. Their findings were published in the journal "Remote Sensing" on April 26.