Along with the climatic change, human water use is also a determining factor that varies the sea level, says a team of researchers from the University of Tokyo, as per a new study published in Nature Geoscience.

It has been noted since long, almost 1.1 millimetres increase occurs in sea-level each year as a combined result of heating of the oceans and melting of ice caps and glaciers. However, another 0.7 millimetres of the total 1.8 millimetres per year rise had remained a puzzle till now.

But, researchers this time have solved the mystery of observed sea-level rise between 1961 and 2003. They have told that it is accounted for by terrestrial water usage, which has increased as a result of population growth.

Also, groundwater reserves have reduced due to increased demand on groundwater reservoirs for irrigation and industrial use, says the team. While artificial reservoirs do not allow water to flow into the seas, deep pools on the contrary evaporate water into the air, causing it to enter seas.

"When people pump groundwater, they may think it's only having local effects. But there are huge implications", says Yadu Pokhrel, a postdoctoral researcher in global hydrology at Rutgers University in New Jersey.