Climate Change Adaptation: Match Crops to Climate

There has been a huge public debate recently about the use of water for agriculture in California, and whether farmers should be growing almonds, alfalfa, and other water-intensive crops in the state.

But California is not all arid desert, as the rainfall map below shows. So the problem is not growing water-intensive crops in California, but growing them in the driest areas in the state. The arid scrubland on the southern floor of the San Joaquin Valley gets about 7-8 inches of rain a year. The farmland in this region was traditionally used for grazing and low-water use crops such as winter wheat. But a huge boom followed the completion of the Central Valley Project and the State Water Project, which brought abundant and cheap Delta water via the Delta-Mendota Canal and the California Aqueduct. The arid land in the southern San Joaquin Valley was relatively inexpensive, and huge tracts became available when the oil companies divested in the 1990s. In the 2000s, a period of relatively wet years and an increase in State Water Project pumping brought even more water to the region. That decade saw an even greater boom in agricultural productivity, farmland value, and farm income. But the 2000s boom was completely unsustainable. The crops that were planted to increase farm income used more water than was available in all but the wettest years. As a result, groundwater levels, which had recovered after the Central Valley Project and State Water Project were completed, began dropping precipitously.

Source: Western Regional Climate Center

Source: USGS California Water Science Center

A major cause of groundwater depletion was the expansion of permanent crops, including almonds and pistachios. Almonds in the southern San Joaquin Valley need about 43-46 inches of water a year, and with cover crops, they need about 53-55 inches. In this very dry region, all but 7 to 8 inches of this water must come from irrigation. The problem is that even in normal years, very few growers get that much surface water. Many get less than two acre feet per acre. So the growers put in wells and pump 1-2 acre feet of water a year, and twice that amount in droughts. Alfalfa, which is grown to feed dairy cows, cattle and sheep in the Tulare Lake region, is also very water intensive. Alfalfa needs about 53-54 inches of water a year. About 45 inches must come from irrigation – almost four acre-feet of water per acre. Almonds and alfalfa are two of the major crops in the Tulare Lake Region, and have greatly expanded. The result has been an enormous drawdown in groundwater in the area, even before the drought.

In a dry year, these crops need even more water, and almost all of it must come from groundwater. These cropping patterns are completely unsustainable. In the critical drought of 2014-2015, they have resulted in drying up of 1,000 wells in Tulare County alone.

Better crops for this arid region include vegetables, which take 22-30 inches of water, and grain and grain hay, which take 23 inches of water. The net irrigation requirement for these crops is about 14-23 inches in a normal year. This would require no extra groundwater in most years, and allow groundwater levels to recover. Switching to row crops, which are more labor intensive, would also increase farmworker employment in the area.

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