Historical Ecology of the Los Angeles River Watershed and Environs, Infrastructure for a Comprehensive Analysis

University of Southern California (USC) | June 15th, 2020

History of Legislation and Policy Formation of the Central Valley Project

U.S. Department of Agriculture (USDA) | March 15th, 1946

History of the Delta Division, Central Valley Project

U.S. Bureau of Reclamation (USBR) | October 1st, 1994

The Delta Division of the Central Valley Project (CVP) acts as the hub around which the CVP revolves. The Delta Division contains the facilities that transfer water from

The Delta Division of the Central Valley Project (CVP) acts as the hub around which the CVP revolves. The Delta Division contains the facilities that transfer water from the Sacramento River, to bolster irrigation supplies to thirsty lands formerly dependent on water from the San Joaquin River. In time, the Delta Division became the hub for controversy revolving around the Central Valley Project. This document recounts the history of the Delta Division.  It was produced by the Bureau of Reclamation.

History of Water Project Conveyance in the Delta

California Natural Resources Agency (CNRA) | January 6th, 2016

A fact sheet on the history of conveyance in  the Delta; includes a timeline from the 1950s to present.  Prepared by the Department of Water Resources.

A fact sheet on the history of conveyance in  the Delta; includes a timeline from the 1950s to present.  Prepared by the Department of Water Resources.

Holocene paleoclimate records from a large California estuarine system and its watershed region: linking watershed climate and bay conditions

Quaternary Science Reviews (Elsevier) | July 10th, 2006

The San Francisco Bay-Delta system includes a watershed that covers a large area of California and provides water to two-thirds of the State's population. Climate

The San Francisco Bay-Delta system includes a watershed that covers a large area of California and provides water to two-thirds of the State's population. Climate over the estuary and its watershed in the dry summer months is controlled by the subtropical high which dominates and deflects storms from California. The subtropical high weakens and migrates south as the Aleutian Low strengthens, bringing wet winter storms to the region. Paleoclimatic records from the Bay and its greater watershed, spanning the Holocene, are reviewed here in order to better understand natural variations of precipitation and runoff and the linkages between those variations and the salinity and ecosystems of the estuary. To better understand regional-scale climate patterns, paleoclimate records from coastal California and the Great Basin are also considered. Large fluctuations in climate have occurred during the period of interest, and there is generally good agreement between the paleoclimate records from different regions. Early Holocene climate throughout California was marked by rising temperatures and reduced moisture as seen in fire records from the watershed. This warmth and aridity peaked about 5000–7000 years ago and was followed by a cooling trend, with variable moisture conditions. The Estuary formed relatively rapidly in response to a high rate of sea level rise that dominated the Holocene until about 6000 years ago, and the subsequent reduced rate of inundation allowed vast tidal marshes to form along the edges of the estuary, which have since been recording changes in environmental conditions. The impacts of changing regional climate patterns are experienced in the San Francisco Bay-Delta system, as altered fresh water flows result in altered estuary salinity. For example, approximately 3800 cal yr B.P., records from throughout the state indicate a cool, moist period, and Bay salinity was reduced; this period was followed by a general drying trend throughout California over the last two millennia, punctuated by decades to centuries-long droughts and brief, extremely wet events. In particular, during the period ca. 1000–800 cal yr B.P. (A.D. 950–1150) conditions seem to have been unusually dry in many parts of the watershed, reducing the fresh water flows to the estuary, and shifting tidal marsh plant assemblages toward less diverse, but more salt-tolerant plants. In contrast, the Little Ice Age (ca. 550–200 cal yr B.P.) brought unusually cool and wet conditions to much of the watershed, and lowered salinity in the Bay. Many reconstructions suggest that notably stable conditions have prevailed over the instrumental period, i.e., after ca. A.D. 1850, even including the severe, short-term anomalies experienced during this period. Interdecadal variability is common in many of the records, with timescales of ca. 55, 70, 90, 100, 150, and 200 years.

How unusual is the 2012–2014 California drought?

American Geophysical Union (AGU) | December 30th, 2014

For the past three years (2012–2014), California has experienced the most severe drought conditions in its last century. But how unusual is this event? Here we use two

For the past three years (2012–2014), California has experienced the most severe drought conditions in its last century. But how unusual is this event? Here we use two paleoclimate reconstructions of drought and precipitation for Central and Southern California to place this current event in the context of the last millennium. We demonstrate that while 3 year periods of persistent below-average soil moisture are not uncommon, the current event is the most severe drought in the last 1200 years, with single year (2014) and accumulated moisture deficits worse than any previous continuous span of dry years. Tree ring chronologies extended through the 2014 growing season reveal that precipitation during the drought has been anomalously low but not outside the range of natural variability. The current California drought is exceptionally severe in the context of at least the last millennium and is driven by reduced though not unprecedented precipitation and record high temperatures.

Hydroclimate response of spring ecosystems to a two‐stage Younger Dryas event in western North America

Nature Portfolio (Springer Nature) | May 5th, 2022

The Younger Dryas (YD) climate event is the preeminent example of abrupt climate change in the recent geologic past. Climate conditions during the YD were spatially compl

The Younger Dryas (YD) climate event is the preeminent example of abrupt climate change in the recent geologic past. Climate conditions during the YD were spatially complex, and high-resolution sediment cores in the North Atlantic, western Europe, and East Asia have revealed it unfolded in two distinct stages, including an initial stable climatic period between ~ 12.9 and 12.2 ka associated with a weakened Atlantic Meridional Overturning Circulation (AMOC) and a second phase characterized by variable conditions until 11.7 ka as the AMOC recovered. Decades of investigations into the climate of western North America during the YD have failed to identify this stepped phenomenon. Here we present hydroclimate data from paleospring deposits in Death Valley National Park (California, USA) that demonstrate unequivocal evidence of two-stage partitioning within the YD event. High groundwater levels supported persistent and long-lived spring ecosystems between ~ 13.0 and 12.2 ka, which were immediately replaced by alternating wet and dry environments until ~ 11.8 ka. These results establish the mid-YD climate transition extended into western North America at approximately the same time it was recorded by hydrologic systems elsewhere in the Northern Hemisphere and show that even short-lived changes in the AMOC can have profound consequences for ecosystems worldwide.

Impacts of the California Drought from 2007 to 2009: Surprising Outcomes for California’s Agriculture, Energy, and Environment

Pacific Institute | June 16th, 2011

California’s three-year drought, which ended with this season’s cool and wet weather, had complicated and serious impacts that have been poorly understood and reporte

California’s three-year drought, which ended with this season’s cool and wet weather, had complicated and serious impacts that have been poorly understood and reported. Some of the impacts were expected; others were surprising. The Pacific Institute has just completed a nine-month assessment of new data from California’s agricultural, energy, and environmental sectors to evaluate actual consequences of the drought for the state. Analysis of state and federal data released over the past year finds that contrary to much of the media reporting, California’s agricultural community proved flexible and resilient, generating agri­cultural revenues in 2007, 2008, and 2009 that were the highest on record. And agriculture-related occupations remained a stable portion of total jobs available in areas directly impacted by water supply restrictions. Less frequently reported were the substantial impacts on energy production and aquatic ecosystems during the drought, which were economically and environmentally significant. “More severe drought is inevitable, and the U.S. – and California in particular – has not reformed drought monitoring, evaluation, planning, and response strategies the way other countries and regions have,” said Juliet Christian-Smith, senior research associate at the Pacific Institute and lead author of the report. “To become more resilient to future droughts, it will be critical to shift from crisis-driven responses to long-term mitigation strategies.” The Pacific Institute analysis, Impacts of the California Drought from 2007-2009, focused on three drought-sensitive sectors: agricultural production, energy production, and ecosystem health.  

Irrigation

Scientific American | January 17th, 1903

Irrigation in California

Scientific American | January 4th, 1890