A recent study of the country’s two major aquifers (the Ogallala Aquifer in the Central Plains and the Central Valley Aquifer in California) finds that major farming regions in the US are consuming groundwater at unsustainable rates. According to the study, over one-third of the southern Great Plains is currently at risk of depleting its groundwater resources within the next 30 years. Groundwater losses have been most significant in the central and southern high plains, which overlies “fossil” water from the melting of the glaciers at the end of the last ice age. Only 4% of the land area above the Ogallala Aquifer (which includes portions of Kansas and Texas) is responsible for about one third of all water losses. In the northern high plains, however, groundwater levels have either remained relatively constant or have increased slightly due to recharge from rain, snowmelt, lakes and rivers. Overall rates of loss from the Ogallala Aquifer averaged 7 cubic km of water between 1987 and 2007.
In California, the aquifer that extends the length of the Central Valley is fed mostly by runoff from precipitation and snowmelt and is also experiencing its most significant water losses in the southern region. This aquifer tends to experience large fluctuations in water loss because growers draw most heavily from it during periods of drought. Extended periods of drought have led to long-term depletion of the aquifer.
Recent research highlights the growing gap between scientific data on depleted groundwater and policies which encourage wiser usage. Many areas, such as the high plains, have only a patchwork of local water management policies. In this case, collaborative regulatory policies, such as multistate compacts, may be required for effective management, although these efforts may depend on the willingness of landowners to comply with an outside regulatory agency.