Monday, September 24, 2012

Using Up the Ogallala- The Groundwater Footprint of the U.S.

The High Plains aquifer commonly known as the Ogallala aquifer (because the Ogallala formation makes up about three quarters of the aquifer) became news and burst into public awareness due to the protests associated with the Keystone XL Pipeline. The Keystone XL Pipeline has been very controversial. Most of the environmental controversy has focused on the porous soils of the Sandhills and fears of a possible oil leak into the Ogallala aquifer which is one of the nation's most important agricultural aquifers. Moving the pipeline away from the aquifer or piping the Canadian oil through British Columbia should mitigate concern for contamination to the Ogallala, but oil leaks are a minor problem. Really, the oil does not move quickly or spread easily through the sedimentary deposits of the High Plains aquifer. There is a much bigger threat to the Ogallala; the aquifer is being depleted because the groundwater within it is predominately non-renewable. This groundwater aquifer that spans and estimated 174,000 square miles is the primary source of water for the High Plains. This was open range land until the groundwater from the aquifer was used to turn the range land into irrigated crops. However, according to John Opie in “Ogallala: Water for a Dry Land” this is essentially fossil water that was generated 10,000-25,000 years ago by the melting of the glaciers of the Rockies.
Water level declines in the High Plains Aquifer since 1958 

The High Plains aquifer is the most intensively used aquifer in the United States and 97% of the water is used for irrigation. Groundwater withdrawals from the High Plains aquifer represent about 20% of all groundwater withdrawals within the United States and have turned the dry range land in the center of the country into the breadbasket of the world. There are only about 2.5 million people living within the High Plains aquifer. With the grains we grow and export we are exporting our water reserves and possibly the future of the region. The High Plains aquifer is being depleted (and contaminated) by irrigation. In the central and southern High Plains water levels have fallen from 50 to more than 150 feet primarily in parts of Kansas, Oklahoma, New Mexico and Texas.  

In  the past year Drs. Tom Gleeson, Yoshihide Wada, Marc F.P. Bierkens and Lodovicus P.H. van Beek each a distinguished voice in groundwater research have pulled together to try to popularize the concept of Groundwater Footprint in order to focus attention on the sustainability of groundwater use. While I think the “global groundwater footprint” is not particularly useful beyond seeing how important groundwater use is globally, their groundwater footprint concept may end up being a very powerful tool. Water is regional and while the authors of “Water Balance of Global Aquifers Revealed by Groundwater Footprint” point out that some groundwater consumption can be transferred to an adjacent aquifer (they use the Upper and Lower Ganges aquifers in India as their example) more often water use and recharge are a dictated by local conditions. An excess of water along the Amazon basin is not particularly useful to Saudi Arabia. However, the authors measurement of “groundwater footprint” is really a measure of groundwater sustainability. A groundwater footprint is a simplified tool to see the water balance between recharge and use of an aquifer and could be used to include groundwater sustainability in developing water, economic and agriculture policies using the virtual water and water footprint analysis. If the water use is not sustainable, then ultimately we are not sustainable.

Groundwater footprint, as the authors point out, could be used with the satellite-based Gravity Recovery and Climate Experiment (GRACE) and Global Land Data Assimilation System (GLDAS) to quantify groundwater depletion. Researchers at the University of California, Irvine, the University of Texas, and the Hydrological Sciences Branch at NASA GSFC have worked in partnership to apply GRACE and GLDAS to real world groundwater monitoring. As these tools develop, the groundwater footprint could end up being an intuitive management tool. The authors found that 80% of the world’s aquifers are not being depleted, but that of the 20% that are being depleted are being depleted at such a vast rate that the global average footprint is of unsustainable groundwater use. In the United States the High Plains and the Central Valley aquifers are being depleted. We as a nation need to examine our agricultural policies and incentives, even our energy policies (corn for ethanol is squandering 40% of the corn crop and the non-renewable water in it to dilute gasoline) and the way we value and price water to ensure that we will have food in the future. 

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