The worst drought in over a century yet agriculture continues to prosper?

Remember the California drought? While it's no longer being reported on as frequently by many news outlets, California has entered it's 6th year of drought, with the most recent U.S Drought Moniter report declaring 43% of the state is considered in extreme-to-exceptional drought. Surely a lack of rainfall this severe would have some some pretty scary implications for America's most productive agricultural region?

Source: US Drought Moniter

Apparently not.

Alongside record-breaking drought statistics, California is also achieving record-high net income figures for the agriculture sector (Grueue, 2015). This seems odd considering agriculture, especially industrial agriculture, is heavily dependent upon freshwater. How can it be possible for agriculture to thrive when there is such a lack of rainfall?

To find the answer to this we have to look underground, literally, because the reason for California's continued agricultural success is groundwater.

Withdrawing water from aquifers is, at the moment, working for California, but it is undeniably only a temporary fix. California therefore is serving as a perfect example of the wide-ranging impacts agriculture has on water and the potential environmental damage this can cause.

An OECD report on the matter describes the global expansion in use of groundwater for irrigation as a 'silent revolution' which has happened over the past 4 decades, enabled by the 'on-demand' nature of groundwater which is not affected by lake or river level variations over short timescales. The advantages of having a constant supply of clean water for irrigation means that in many countries withdrawals have exceeded natural recharge rates.

In California, groundwater abstractions have been vital in sustaining agriculture for over a decade and there is certainly a case to say that abstractions even before the onset of drought were unsustainable. The Gravity Recovery and Climate Experiment (GRACE), which was launched in 2002, takes measurements of the Earth's gravity field, from which information about natural systems can be inferred. Using this satellite data Famiglietti and others (2011) estimated a 31km³ loss in groundwater storage between 2006 and 2012. A more recent study (Howitt et al, 2014) then found a further 6.3km³ loss in only two years of drought between 2012 and 2014.

What does this mean for California?

In the short term excessive groundwater pumping can cause a number of environmental changes. One of these is sea-water intrusion. When groundwater is extracted from coastal aquifers the equilibrium between saltwater and freshwater at the aquifer-sea boundary shifts in the favour of sea water. This means that as groundwater levels decline, saltwater diffuses into the soils making them saline. Saltwater intrusion therefore spoils vital water sources both for human  and non-human use. 

Another environmental change caused by unsustainable groundwater abstractions is land subsidence. As the total volume of water held in soils drastically declines, the subsoil compacts, reducing in volume, allowing the land to be lowered, which can have devastating effects on infrastructure. This effect reduces the capacity of the aquifer to hold water in the future and is likely irreversible. Just take a look at this map which shows areas where subsidence has been attributed to groundwater abstraction. California's list goes on and on! 

Source: http://water.usgs.gov/edu/earthgwlandsubside.html

In the long term, California's overuse of groundwater could have serious implications.The problem will only get worse, groundwater quality will continue to decline, and water stress will increase. All of this in a time where the future looks to be even hotter and even drier. The end of Californian agricultural powerhouse?

State agencies such as the Department of Water Resources and State Water Resources Control Board have been tasked with overseeing new legislation that regulates groundwater abstraction in 127 of the most 'at risk' water basins. Management plans must be set up by 2022 and must ensure water use in their respective regions is fair and sustainable. But sustainable water use is likely to reduce agricultural output from the region and so the new legislation is not without significant opposition. Many farmers have already shown apprehension, where for the past century landowners have had free access to any and all of the water found beneath their land.  It's a difficult situation which triggers a number of opposing laws in the US and it is therefore expected that many major players will attempt to sue basin management agencies.

Final thoughts...

Slightly off-topic this week, although I think the story of California serves as a great example of the struggle between maintaining/increasing profit while preserving the environment and it's resources. Even in the face of sever environmental changes and water stresses, it is still incredibly difficult for legislation to be passed that can curb the activities of such profit driven industries. In fact many of the particularly commercial farms may be able to bypass new groundwater legislation using expensive legal processes. It will be interesting to see how the situation progresses in California, who are the winners and who are the losers, and ultimately at what point does the condition of the environment truly become the main priority.