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California Drought Is Over, but Data Highlights State’s Challenges Ahead

15 August 2019

California was declared “free of drought” in March by the National Drought Mitigation Center after more than seven years of critically dry conditions. But the state still has much to do to come to terms with its intense water usage, especially for the roughly 400 different agricultural commodities produced there.

An immediate risk stems from the wet and cool winter that helped bring the drought to an end, which boosted soil moisture and prompted explosive vegetative growth throughout the state this spring. That in turn will contribute to a significantly greater fuel load for wildfires in late summer and fall in what could be a ‘very active’ wildfire season, the National Interagency Fire Center has warned.

California suffered devastating wildfires last year. This map of Northern California makes use of satellite-based NDVI readings as of December 2018 to show the extent of the fire damage, represented by the dark orange areas. Click on the image to view in the Gro web app. NDVI, a measure of vegetative health, is viewable in the web app to a granularity of 250 meters per pixel.

An end to official drought status was followed in short order by record high July temperatures in Southern California and the Central Valley, stressing crops and stepping up demand on the state’s water supplies. Most cropland in California, a major producer of tree nuts and fruit, is irrigated. Under state law—the Sustainable Groundwater Management Act—some 21 critically overdrawn groundwater basins must submit proposals by early next year to show how they will replenish their repositories over the next 20 years. Farm groups had raised concerns the law could devalue land prices, affecting the viability of some farms and businesses.

As a result of last month’s triple-digit temperatures, the percentage of California cropland topsoil moisture rated “very short” by USDA NASS has held steady at 65% since mid-July, the highest percentage in the past five years. Current reports indicate that crop conditions for oranges, prunes, avocados, and forage have taken a hit from heat stress. Still, evapotranspiration data shows no major vegetative health issues within California’s major agricultural centers, as controlled irrigation offsets much of the depletion in soil moisture.

The maps above draw attention to cropland in California’s Central Valley, which houses much of the state’s agricultural production. The map on the left highlights the low soil moisture readings throughout the valley (red, orange, yellow). The map on the right shows evapotranspiration, where areas shaded in red indicate lower than average evapotranspiration and poorer vegetative health and the areas shaded in green indicate higher than average evapotranspiration and better than average vegetative health. Some crop stress is apparent in the western part of the Central Valley, but the eastern edge appears healthy at the moment. Click on the image to view an interactive chart in the Gro web app.

California accounts for one-third of all US vegetables and two-thirds of all fruits and nuts. Almonds and pistachios are significant players in California’s agricultural economy, contributing nearly a third of the state’s export revenue. A devastating drought in 2015 killed many of these tree crops, but irrigated acreage for both almond and pistachio trees has rebounded in the years since.

Despite total area bearing increasing for both nuts in recent years, yields haven’t changed at all in the past decade. Farmers cite nagging issues with temperature and soil moisture. Warmer than average winters in recent years have had a negative impact on the productivity of tree crops. Current models indicate 40% declines in avocado yields and 20% declines in orange, walnut, and grape yields by 2060.

Almond and pistachio harvests are currently underway in California. In 2019, the state is expected to produce a record 2.5 billion pounds of almonds.

Alfalfa production in California, mainly for dairy feed, is a major user of water. The area dedicated to alfalfa has dropped sharply in the past decade as farmers switch away from the costly, water-intensive crop. Increased restrictions on groundwater use have incentivized farmers to produce crops that are less reliant on water or are more lucrative, like almonds. Acreage dedicated to stone fruit production has also tumbled in recent years. Peaches and nectarines require a lot of water to produce, but are not as lucrative as almonds and pistachios. Click on the image to view an interactive chart in the Gro web app.
Almond production accounts for nearly 10% of California’s total agricultural water use. Still, acreage dedicated to almonds continues to increase. In 2017, almonds accounted for roughly 27% of California’s total agricultural export revenue. Click on the image to view an interactive chart in the Gro web app.
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