Some notes from a talk this morning by Dr. Bridget Scanlon, delivered in a lovely Irish lilt occasionally disrupted by vaguely disturbing Texanisms like “folks”.
– For the first time, the LCRA (our local water authority) has cut off supplies to rice farmers.
– Money can buy water. More specifically, money can buy energy, and energy can buy water. But then there are energy constraints…
– Irrigation amounts to 70 % of fresh water use (in US?) . 40% of freshwater supplies are mined.
– Irrigated lands are 30% of cropland but produce 70% of crops by value.
– depletion occurs maximally toward the equatorward edge of an aquifer. Nebraska is not being drawn down, Kansas has over two centuries left, Texas half that, some localities much less. (I was surprised that the time frame is that long, to be honest.) Ogalalla is 8% depleted.
– ground water and surface water in many places are parts of the same system and it doesn’t matter which one is withdrawn. Australians in particular are confused about this in management of the Murray-Darling system, their main agricultural zone.
– significant water withdrawals directly or indirectly from surface waters impact endangered species, ecosystems
– GRACE data is verified by local measurements in US aquifers; resolution is adequate for Ogallala, marginal for California central valley
– in parts of California so much water has been withdrawn that there has been as much as 10 meters of subsidence of the surface
– more efficient drip systems can help
– groundwater withdrawal is a term in sea level rise
The most interesting point in my opinion was a generalization that Dr Scanlon made: “As a general rule sustainability trades off against reliability.” She even made a schematic graph, which I thought was taking it a bit far. But the point is worth considering.
map – USGS via loe.org