Drought and the Sacramento–San Joaquin delta, 2012–2016: Environmental review and lessons

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Droughts are common in California. The drought of 2012-2016 had no less precipitation and was no longer than previous historical droughts, but came with record high temperatures and low snowpack, which worsened many drought impacts. Water supplies for agriculture and urban users statewide struggled to meet water demands. Conservation and rationing, increased groundwater pumping and a diversified economy helped keep California’s economy robust in most sectors. The drought degraded environmental conditions in the Sacramento-San Joaquin Delta (Delta) as the region became saltier and warmer, invasive weeds spread, and iconic fishes like salmon and Delta smelt had strong declines.

Water demands on the Delta often outstrip its capacity, even in wetter than average years. During the drought, water-demand conflicts increased among human and environmental uses. For example, maintaining Delta outflow and freshwater standards was important to agriculture, drinking water supplies and some sensitive species. To fulfill these downstream needs, upstream water releases from Shasta Reservoir depleted the cold-water pool in 2014 and 2015, increasing Sacramento River temperatures and nearly extinguishing two cohorts of winter-run Chinook salmon.

To help understand scientific aspects of Delta management during the drought, we reviewed official documentation, reports and data, and spoke with numerous agency managers and scientists (Durand et al. 2020).  State and federal water management priorities for the Delta watersheds were to (1) provide essential human health and safety needs, (2) control saltwater intrusion in the Delta, (3) maintain reservoir capacity, and (4) protect at-risk species. Support for these priorities included reducing reservoir releases, Delta export pumping, and Delta outflow; installing an in-Delta salinity barrier; conserving urban water; reducing agricultural water allotments; increasing salmon hatchery production and trucking; and removing invasive aquatic weeds.

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