A study by the U.S. Geological Survey (USGS) released this week has found that draw-down from long-term aquifers has been accelerating driven in large part by water use for irrigation.
These two maps, the first from the USGS report showing depletion hotspots, and the second from the United States Department of Agriculture showing the US's main wheat growing regions, provide a clear visual of the correlation between groundwater depletion and agriculture.
According to the USGS report:
The cumulative volume of groundwater depletion in the United States during the 20th century is large-totalling about 800 cubic kilometres (km3) and increasing by an additional 25 percent during 2001-2008 (to a total volume of approximately 1,000 km3).
The rate of groundwater depletion has increased markedly since about 1950, with maximum rates occurring during the most recent period (2000-2008) when the depletion rate averaged almost 25 km3 per year (compared to 9.2 km3 per year averaged over the 1900-2008 timeframe).
The study assessed long-term groundwater depletion in 40 separate aquifer systems or subareas to build a national overview of groundwater depletion (defined as a reduction in the volume of groundwater in storage in the subsurface). The figure below taken from the report shows the proportion of depletion due to irrigation (green shaded portion) in the Death Valley aquifer in California.
Click here to read the full report, Groundwater Depletion in the United States 1900-2008.