Climate Number: 28 Cubic Miles
Each year the United States pumps about 28 cubic miles of water out its groundwater aquifers – natural underground storage areas – for irrigation, drinking water, industrial purposes, etc. While about 84.6 percent of these withdrawals are recharged to the aquifers through natural recharge (primarily rainfall) or artificial recharge (recharge to the groundwater from human activities), 15.4 percent, or about 4.25 cubic miles, of America’s groundwater withdrawals flow into the oceans without being returned as rainfall. Globally, about 34 cubic miles of groundwater is lost to the oceans every year. While groundwater losses can be replenished over time, losses from arid or semi-arid regions may take thousands of years to recover. Much of the groundwater being pumped from underneath the Great Plains region, for example, is fossil groundwater that was deposited by the melting North American Ice Sheet over 10,000 years ago.
For comparison: The 34 cubic miles of groundwater sent to the oceans raises global sea levels by 0.39 millimeters each year, which is a significant fraction of the total 2.1 millimeter annual sea-level rise. Sea level rise from the water coming off the shrinking Greenland and Antarctic Ice Sheets is about 1.3 millimeters per year.
Source: Church, JA et al. “Revisiting the Earth’s sea-level and energy budgets from 1961 to 2008.” Geophysical Research Letters 38 (2011): L18601.