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Abstract

The irrigation regions of Australia’s southern Murray-Darling Basin (SMDB) and California’s Central Valley provide several contrasts. In the SMDB, reliance on groundwater is relatively limited. In drought, groundwater usage may double but it covers no more than one tenth or so of the shortfall in surface water availability. In the Central Valley, groundwater has compensated for a much larger share of the shortfall in surface water in the prolonged drought which started in 2013. A common feature of the two irrigation regions is that they both have extensive irrigated infrastructure. But in allocating water, that is where the similarity ends. Ongoing reforms in Australia’s water management have resulted in a separation of land and water ownership. With this have come water exchanges and local brokers and hence the ability to move water from annual to perennial activities during drought. In the Californian case, appurtenant water rights have provided a barrier to water trading. Such trading at best proceeds on an informal basis in thin volumes. The lack of water trading has an environmental consequence, with more wells being dug to provide water for existing plantations. This may worsen land subsidence and aquifer depletion.

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