Sacramento River

How can we support the development of robust groundwater sustainability plans?

California Agriculture (UCANR) | March 13th, 2018

Three years after California passed the Sustainable Groundwater Management Act (SMGA), groundwater sustainability agencies (GSAs) are now preparing to develop their groun

Three years after California passed the Sustainable Groundwater Management Act (SMGA), groundwater sustainability agencies (GSAs) are now preparing to develop their groundwater sustainability plans (GSPs), the blueprints that will outline each basin’s road to sustainability. Successful GSPs will require an effective participatory decision-making process. We tested a participatory process with the Yolo County Flood Control and Water Conservation District, a water-limited irrigation district in the Central Valley. First, we worked with district stakeholders to outline the parts of the plan and set measureable objectives for sustainability. The district defined seven management strategies, which the research team evaluated against climate, land use and regulatory uncertainties using a water resources model. Together, we explored model results using customized interactive graphics. We found that the business-as-usual strategy was the most unlikely to meet sustainability objectives; and that a conjunctive use strategy, with winter groundwater recharge and periphery ponds storage, achieved acceptable measures of sustainability under multiple uncertainties, including a hypothetical pumping curtailment. The process developed a shared understanding of the vulnerabilities of the local groundwater situation and proved valuable in evaluating strategies to overcome them.

How Much Snow?

Scientific American | March 1st, 1939

Last winter, at 682 different locations in the Rockies and high Sierras, more than 30,000 exact measurements of snow depth and water content were taken, in order to e

Last winter, at 682 different locations in the Rockies and high Sierras, more than 30,000 exact measurements of snow depth and water content were taken, in order to estimate how much water the mountain snowfields would supply in the run-off during summer months. To make this survey cost more than $100,000. On it was predicated the expenditure, and saving, of millions. While the science of surveying snow is still in its infancy, its extent and importance are increasing rapidly. Ridiculed at first, in the last few years it has taken on world-wide aspects. To grasp its significance in our western states, picture a series of snow-covered mountain ranges that by their streams make life possible in dry intervening valleys. Abundant snow means abundant water. Abundant water means power, and cheap electricity. More important still, it means abundant crops. Dearth of snowfall in the mountains means dry river beds in August, machinery standing idle, thirsty cattle, and dying plants.

Human contributions to evapotranspiration mitigate swings in dry-to-wet year transitions

Nature Portfolio (Springer Nature) | January 9th, 2026

California’s food and economic security depends on water availability, particularly under increasingly extreme climate scenarios. A key component of the water balance i

California’s food and economic security depends on water availability, particularly under increasingly extreme climate scenarios. A key component of the water balance is evapotranspiration, the combination of soil and surface evaporation and plant transpiration. Evapotranspiration is influenced by natural drivers (e.g., climate, vegetation cover) and human intervention (e.g., irrigation, land management). Here, we analyze the transition between one of California’s driest years (2022) to an exceptionally wet year (2023) to assess evapotranspiration responses to climate extremes. Despite increased precipitation, total statewide evapotranspiration changed less than 10%. In 2022, human contributions accounted for 30% of statewide evapotranspiration and 80% in managed lands. In 2023, natural evapotranspiration increased, and human contributions fell by 30%, yet still comprised nearly 50% of evapotranspiration in managed areas. Our findings underscore the enduring role of human activity on California’s hydrology, even during wet years, and demonstrate a framework to separate natural and anthropogenic controls on evapotranspiration.

Human emissions drive recent trends in North Pacific climate variations

Nature Portfolio (Springer Nature) | August 14th, 2025

Click here for a plain language discussion of the article by co-authors Pedro N. DiNezio and Timothy M. Shanahan

Click here for a plain language discussion of the article by co-authors Pedro N. DiNezio and Timothy M. Shanahan

Human viral nucleic acids concentrations in wastewater solids from Central and Coastal California USA

Nature Portfolio (Springer Nature) | June 22nd, 2023

Human-Induced Changes in the Hydrology of the Western United States

American Association for the Advancement of Science (AAAS) | February 22nd, 2008

Observations have shown that the hydrological cycle of the western United States changed significantly over the last half of the 20th century. We present a regi

Observations have shown that the hydrological cycle of the western United States changed significantly over the last half of the 20th century. We present a regional, multivariable climate change detection and attribution study, using a high-resolution hydrologic model forced by global climate models, focusing on the changes that have already affected this primarily arid region with a large and growing population. The results show that up to 60% of the climate-related trends of river flow, winter air temperature, and snow pack between 1950 and 1999 are human-induced. These results are robust to perturbation of study variates and methods. They portend, in conjunction with previous work, a coming crisis in water supply for the western United States.

Human-wildlife conflict is amplified during periods of drought

American Association for the Advancement of Science (AAAS) | November 12th, 2025

Climate change–induced alterations to human-wildlife interactions are recognized to pose a fundamental challenge for global conservation initiatives. However, the exten

Climate change–induced alterations to human-wildlife interactions are recognized to pose a fundamental challenge for global conservation initiatives. However, the extent to which specific climatic disturbances influence dynamics of human-wildlife conflict across different taxonomic groups remains poorly understood. Here, we leverage an extensive dataset of community-derived human-wildlife conflict incidents to examine the influence of drought, represented by the variation in summed precipitation over the prior 12 months, on conflict reporting. We show that prolonged decreases in precipitation are associated with increased overall conflict occurrences across taxa and are significantly associated with increased conflict with carnivore species in particular. A future with increasingly severe and frequent droughts could lead to resource scarcity that not only causes conflict between humans but also between humans and the natural world around them.

Hydraulic and mechanical properties affecting ground‐water flow and aquifer‐system compaction, San Joaquin Valley, California

U.S. Geological Survey (USGS) | July 19th, 2001

This report summarizes hydraulic and mechanical properties affecting ground-water flow and aquifer-system compaction in the San Joaquin Valley, a broad alluviated inte

This report summarizes hydraulic and mechanical properties affecting ground-water flow and aquifer-system compaction in the San Joaquin Valley, a broad alluviated intermontane structural trough that constitutes the southern two-thirds of the Central Valley of California. These values will be used to constrain a coupled ground-water flow and aquifer-system compaction model of the western San Joaquin Valley called WESTSIM. A main objective of the WESTSIM model is to evaluate potential future land subsidence that might occur under conditions in which deliveries of imported surface water for agricultural use are reduced and ground-water pumping is increased. Storage values generally are components of the total aquifer-system storage and include inelastic and elastic skeletal storage values of the aquifers and the aquitards that primarily govern the potential amount of land subsidence. Vertical hydraulic conductivity values generally are for discrete thicknesses of sediments, usually aquitards, that primarily govern the rate of land subsidence. The data were compiled from published sources and include results of aquifer tests, stress-strain analyses of borehole extensometer observations, laboratory consolidation tests, and calibrated models of aquifer-system compaction.

Hydroclimate Report Water Year 2018

California Department of Water Resources (DWR) | March 31st, 2020

Water year (WY) 2018 whipsawed from dry to wet and added high heat for the summer. The WY ended with 82 percent of average precipitation in the Northern Sierra and 20 per

Water year (WY) 2018 whipsawed from dry to wet and added high heat for the summer. The WY ended with 82 percent of average precipitation in the Northern Sierra and 20 percent below average April-July streamflow in the Sacramento River and 19 percent below average for the San Joaquin River. Peak statewide snowpack was only 60 percent of average. While precipitation and stream flow were below average, the big story of the 2018 WY were record temperatures that lead to several unprecedented and deadly wildfires in the state.

Hydroclimate Report Water Year 2019

California Department of Water Resources (DWR) | June 30th, 2020

Water year (WY) 2019 continued to demonstrate effects of climate change with greater variability and more extremes. Hydroclimate extremes presented themselves with atmosp

Water year (WY) 2019 continued to demonstrate effects of climate change with greater variability and more extremes. Hydroclimate extremes presented themselves with atmospheric rivers causing both flooding and heavy snowpack. Before the wet winter and spring months, California experienced a very dry fall in where the devastating Camp Fire started on November 8, 2018 in Butte County. Fall transitioned to into a wet winter with 64 percent of the WY total for the DWR Northern 8-station index falling in the three months of January, February and March. Temperatures went from extreme cold in February to hot in August as the year progressed from winter to summer.