By Claire

New research out of the Netherlands suggests that groundwater that is pumped to the surface may contribute more to sea level rise than melting from glaciers and ice caps, excluding Greenland and Antarctica.

The groundwater we pump to the surface for irrigation, drinking water, and industrial uses, doesn’t just seep back into the ground — it also evaporates into the atmosphere, or runs off into waterways, eventually emptying into the world’s oceans. 

Researchers were able to estimate the impact of groundwater depletion since 1900 using data from individual countries on groundwater pumping, model simulations of groundwater recharge, and reconstructions of how water demand has changed over the years.

Using these rates, they calculated that about 204 cubic kilometres of groundwater globally had been pumped in 2000, most of which was used for irrigation. Much of this irrigation water, in turn, evaporates from plants, enters the atmosphere and falls back to earth as rain.

Taking into account the seepage of groundwater back into the aquifers, as well as evaporation and runoff, the team estimated that groundwater pumping resulted in a sea level rise of about 0.57 mm in 2000 — much greater than the 1900 annual sea level rise of 0.035 mm.

The latest IPCC report in 2007 estimated the likely influence of terrestrially sourced water on global sea level rise, however, these estimates did not take groundwater into consideration. This variable has been considered to be too uncertain to include in model simulations.

If things continue as projected, the researchers estimate that by 2050, the net cumulative effect of non-ice, land-based water sources and reservoirs — including groundwater pumping, marsh drainage, dams, and more — will have added 31 mm to sea level rise since 1900.

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