After something of a hiatus do to work obligations, I’m back. And I think I should start off my return to regular (or at least more regular) posting with a positive story.
A new report has just been issued by the Pacific Water Institute, home to Peter Gleick, a much admired voice among those concerned with water related issues.
The eponymous subject of the report is “California Farm Water Success Stories,” and its purpose is to highlight examples of farmers in California who have made significant strides to increase the efficiency of their water usage. There is even a short video that accompanies the report that you can find here.
So why do you care? You care because agriculture is far and away the single most significant consumer of potable water in United States, and the world. As a result, any increases in agriculture’s water efficiency can have a dramatic effect on water supplies. Currently this is a critical issue in California and much of the southwestern United States.
The thrust of the report is that solving California’s water shortage requires increasing the efficiency with which Californians, and particularly farmers, use water. Moreover, increasing efficiency by a significant amount (one farm estimates it reduced its water consumption by 20%) is achievable with existing technology and at a cost equivalent to or less than that required to increase supply – and without the attendant negative environmental impacts.
It is an interesting report, and reinforces the fact that there are practical solutions to water scarcity that do not require us to sacrifice the environment.
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You cite the report as saying that "one farm estimates it reduced its water consumption by 20%". Was the actual consumptive water use reduced by 20%? Or was the water diverted and applied reduced by 20%? There is a difference.
ReplyDeleteIn any hydrologic system where the water supply and the water sink (where non-consumptive water uses go) are the same, increasing irrigation application efficiency just eliminates the sink supply and provides a higher percentage of the applied water to consumptive use crop production. You can pump less water with the higher efficient irrigation system, but you can also actually consume more water.
The 65% efficient irrigation system only makes 65% of the applied water available for crop production. The rest is non-consumptive use that returns (eventually) to the supply - at least in a traditional groundwater aquifer system. When a new 99% efficient drip system is installed, the producer pumps 75% of what he used to, but 99% of it is made available and consumed by crop production. My math tells me that 99% of 75% is more than 65% of 100%.
It is this extra water use that increases the yields so often reported when higher efficiency systems are converted to.
When the sink is different than the supply, and no one else is using the sink water, the efficiency upgrades are clearly a good thing, but these situations exist much less often.
We evaluated the first new irrigation technology conversions in our groundwater management district - flood irrigation to subsurface drip (SDI) and in every case the SDI used more water consumptively than the flood systems. Most often the higher efficiency system allowed them to pump less, so additional acres were added to utilize the extra water. What good business person would not make that decision after paying $1000 or more per acre for the new system?
Don't get me wrong, the SDI systems are very efficient and have other benefits for the irrigation operation's bottom line, but water conservation (reduced consumptive water use) is usually not one of them.
Because consumptive water use is the cause of aquifer storage changes (water level declines) in a typical aquifer system, anything that increases consumptive water use will increase the decline rate - even if less water is pumped.
I remain amazed at how much money is being directed at irrigation efficieny upgrades as a solution to aquifer overdrafts. I am perhaps even more amazed that many of these efforts are in areas where new water development is still allowed. Under these circumstances, the problems are only destined to get worse.
Mr. Bossert,
ReplyDeleteThank you for the post. I actually found it so insightful (to me at least), that I have made it the focus of my most recent post, which you can find here:
http://thewaterlaw.blogspot.com/2010/04/when-does-efficiency-not-lead-to.html