Water Depletion

Michael Specter. October 23, 2006. The Last Drop. Confronting the possibility of global catastrophe. The New Yorker.

Cyanobacteria

Brookes, J., et al.  7 Oct 2011. Resilience to Blooms. Science.
Explosive cyanobacterial blooms cause disease in humans and livestock, and make treating water more expensive.  There are more episodes now due to increasing deforestation, climate change, human and commercial animal waste, and agricultural fertilization.

Groundwater Depletion

28 May 2012. Groundwater Depletion in Semiarid Regions of Texas and California Threatens US Food Security.  The nation’s food supply may be vulnerable to rapid groundwater depletion from irrigated agriculture.  This study is from the journal Proceedings of the National Academy of Sciences, and show that groundwater depletion is causing rural populations to decrease in the High Plains, cities are replacing farms in the Central Valley, and during droughts some farmers are forced to fallow their land. These trends will only accelerate as water scarcity issues become more severe.

Three results of the new study are particularly striking:
1) during the most recent drought in California’s Central Valley, from 2006 to 2009, farmers in the south depleted enough groundwater to fill the nation’s largest human-made reservoir, Lake Mead near Las Vegas — a level of groundwater depletion that is unsustainable at current recharge rates.
2) 33% of the groundwater depletion in the High Plains occurs in just 4% of the land area.
3) if current trends continue some parts of the southern High Plains that currently support irrigated agriculture, mostly in the Texas Panhandle and western Kansas, will be unable to do so within a few decades.

California’s Central Valley is the nation’s “fruit and vegetable basket.”
The High Plains are  the country’s “grain basket.”
Combined, these 2 regions account for much of the nation’s food production.
They also account for half of all groundwater depletion in the U.S., mainly as a result of irrigating crops.

For various reasons, Scanlon and other experts don’t think these or other engineering approaches will solve the problem in the High Plains. When groundwater levels drop too low to support irrigated farming in some areas, farmers there will be forced to switch from irrigated crops such as corn to non-irrigated crops such as sorghum, or to rangeland. The transition could be economically challenging because non-irrigated crops generate about half the yield of irrigated crops and are far more vulnerable to droughts.

10 Feb 2011. Lettuce is sucking California’s fruit basket dry.  California’s Central valley – the most productive farmland in the US – is being sucked dry. Over 12 years, about 12 cubic miles of water were lost, which is not sustainable — scientists estimate the valley could run dry by 2100. Green vegetables require a lot of water, and groundwater pumping is not regulated.