Precipitation variability increases in a warmer climate

Nature Portfolio (Springer Nature) | December 21st, 2017

Understanding changes in precipitation variability is essential for a complete explanation of the hydrologic cycle’s response to warming and its impacts. Whil

Understanding changes in precipitation variability is essential for a complete explanation of the hydrologic cycle’s response to warming and its impacts. While changes in mean and extreme precipitation have been studied intensively, precipitation variability has received less attention, despite its theoretical and practical importance. Here, we show that precipitation variability in most climatemodels increases over a majority of global land area in response to warming (66% of land has a robust increase in variability of seasonal-mean precipitation). Comparing recent decades to RCP8.5 projections for the end of the 21st century, we find that in the global, multi-model mean, precipitation variability increases 3–4% K−1 globally, 4–5% K−1 over land and 2–4% K−1 over ocean, and is remarkably robust on a range of timescales from daily to decadal. Precipitation variability increases by at least as much as mean precipitation and less than moisture and extreme precipitation for most models, regions, and timescales. We interpret this as being related to an increase in moisture which is partially mitigated by weakening circulation. We show that changes in observed daily variability in station data are consistent with increased variability.

Predicted Water-Level and Water-Quality Effects of Artificial Recharge in the Upper Coachella Valley, California, Using a Finite-Element Digital Model

U.S. Geological Survey (USGS) | April 15th, 1978

This study was begun in mid-1973 by the U.S. Geological Survey in cooperation with the Desert Water Agency (DWA) and the Coachella Valley County Water District (CVCWD). T

This study was begun in mid-1973 by the U.S. Geological Survey in cooperation with the Desert Water Agency (DWA) and the Coachella Valley County Water District (CVCWD). The purpose of the study was to (1) analyze the present water quality conditions of the ground-water basin, (2) determine the water-level changes that will result from recharging the aquifer, and (3) determine the water-quality changes that will result from recharging the aquifer. The study included: (1) Collecting, evaluating, tabulating, and computer processing all available ground-water-quality data for the study area; (2) describing the areal distribution of water quality throughout the ground-water basin; (3) updating the pumpage and other hydrologic data compiled for the analog model of the study area (Tyley, 1974); (4) developing a digital hydraulic (flow) model utilizing the finite-element method; and (5) developing a digital solute-transport (water quality) model utilizing the finite-element method. This report presents the results of the 3-year study and the predictions of the possible effects of ground-water recharge on the water resources of the upper Coachella Valley.

Predicting Streamflow Elasticity Based on Percolation Theory and Ecological Optimality

American Geophysical Union (AGU) | July 20th, 2023

Preliminary Evaluation of Impacts of Potential Groundwater Sustainability Indicators on Future Groundwater Extraction Rates – Oxnard Plain and Pleasant Valley Groundwater Basins

United Water Conservation District (UWCD) | April 4th, 2017

This evaluation was performed to estimate the combined sustainable yield of the Oxnard Plain (including the Forebay) and Pleasant Valley groundwater basins (the study are

This evaluation was performed to estimate the combined sustainable yield of the Oxnard Plain (including the Forebay) and Pleasant Valley groundwater basins (the study area). The purpose is to provide supporting information to United Water Conservation District’s (United) management and Board of Directors in establishing groundwater management policies that are consistent with the mission of the agency. United recognizes that the compliance actions associated with the Sustainable Groundwater Management Act (SGMA), the formation of a Groundwater Sustainability Agency (GSA), and the creation and implementation of Groundwater Sustainability Plans (GSPs) have the potential to change how groundwater resources are managed in Ventura County. This report was prepared for the benefit of United’s Board of Directors and senior management, and is not intended to serve as a GSP, define how the sustainable yield should be determined by the GSA, or specify what value or range of values should be used as the sustainable yield. The analyses and results are meant to be used as a starting point in evaluating potential impacts to United’s operations as a result of sustainability planning already underway by the Fox Canyon Groundwater Management Agency (FCGMA) for the study area. Note: an addendum to this was published on November 7, 2017

Preliminary Evaluation of the Hydrogeologic System in Owens Valley, California

U.S. Geological Survey (USGS) | January 8th, 1988

Owens Valley is a major source of water for southern California and presently (1986) provides more than 60 percent of the supply for Los Angeles. Since 1970, ground-water

Owens Valley is a major source of water for southern California and presently (1986) provides more than 60 percent of the supply for Los Angeles. Since 1970, ground-water withdrawal from Owens Valley has increased, and a decline in the health of vegetation has been reported. In 1982, a cooperative project to study the hydrogeology and plant ecology of Owens Valley was begun by Inyo County, the Los Angeles Department of Water and Power, and the U.S. Geological Survey. As part of this project, the available data and present hydrologic concepts of Owens Valley were evaluated by using a ground-waterflow model. Results of this preliminary evaluation are being used to guide data collection and the development of more sophisticated hydrologic models.

Preliminary hydrogeologic assessment near the boundary of the Antelope Valley and El Mirage Valley groundwater basins, California

U.S. Geological Survey (USGS) | July 19th, 2017

Primary Production in the Delta: Then and Now

University of California, Davis (UC Davis) | October 3rd, 2016

To evaluate the role of restoration in the recovery of the Delta ecosystem, we need to have clear targets and performance measures that directly assess ecosystem function

To evaluate the role of restoration in the recovery of the Delta ecosystem, we need to have clear targets and performance measures that directly assess ecosystem function. Primary production is a crucial ecosystem process, which directly limits the quality and quantity of food available for secondary consumers such as invertebrates and fish. The Delta has a low rate of primary production, but it is unclear whether this was always the case. Recent analyses from the Historical Ecology Team and Delta Landscapes Project provide quantitative comparisons of the areal extent of 14 habitat types in the modern Delta versus the historical Delta (pre-1850). Here we describe an approach for using these metrics of land use change to: (1) produce the first quantitative estimates of how Delta primary production and the relative contributions from five different producer groups have been altered by large-scale drainage and conversion to agriculture; (2) convert these production estimates into a common currency so the contributions of each producer group reflect their food quality and efficiency of transfer to consumers; and (3) use simple models to discover how tidal exchange between marshes and open water influences primary production and its consumption. Application of this approach could inform Delta management in two ways. First, it would provide a quantitative estimate of how large-scale conversion to agriculture has altered the Delta's capacity to produce food for native biota. Second, it would provide restoration practitioners with a new approach—based on ecosystem function—to evaluate the success of restoration projects and gauge the trajectory of ecological recovery in the Delta region.

Probabilistic estimates of future changes in California temperature and precipitation using statistical and dynamical downscaling

Climate Dynamics (Springer) | March 30th, 2012

Sixteen global general circulation models were used to develop probabilistic projections of temperature (T) and precipitation (P) changes over California by the 2060s.

Sixteen global general circulation models were used to develop probabilistic projections of temperature (T) and precipitation (P) changes over California by the 2060s. The global models were downscaled with two statistical techniques and three nested dynamical regional climate models, although not all global models were downscaled with all techniques. Both monthly and daily timescale changes in T and P are addressed, the latter being important for a range of applications in energy use, water management, and agriculture. The T changes tend to agree more across downscaling techniques than the P changes. Year-to-year natural internal climate variability is roughly of similar magnitude to the projected T changes. In the monthly average, July temperatures shift enough that that the hottest July found in any simulation over the historical period becomes a modestly cool July in the future period. Januarys as cold as any found in the historical period are still found in the 2060s, but the median and maximum monthly average temperatures increase notably. Annual and seasonal P changes are small compared to interannual or intermodel variability. However, the annual change is composed of seasonally varying changes that are themselves much larger, but tend to cancel in the annual mean. Winters show modestly wetter conditions in the North of the state, while spring and autumn show less precipitation. The dynamical downscaling techniques project increasing precipitation in the Southeastern part of the state, which is influenced by the North American monsoon, a feature that is not captured by the statistical downscaling.

Probabilistic Subsidence Forecast Model for the California Aqueduct Subsidence Program, San Joaquin Valley, California: Revision 1 Design Report

California Department of Water Resources (DWR) | October 4th, 2024

This report documents the development of a probabilistic subsidence forecast model for simulating a plausible range of future land-surface altitude conditions along the C

This report documents the development of a probabilistic subsidence forecast model for simulating a plausible range of future land-surface altitude conditions along the California Aqueduct (Aqueduct) and San Luis Canal in the San Joaquin Valley (SJV), with an emphasis on areas of localized subsidence (i.e., “subsidence bowls”). The model forecasts will be used to inform long-term planning and on-going analyses of potential investments needed to provide a suitable level of performance for the Aqueduct. The forecast model is primarily based on an empirical relationship between historical subsidence rates and annual water deliveries from the Central Valley Project (CVP) and State Water Project (SWP). A key assumption of the model is that the rate of groundwater overdraft, which contributes to loss of aquifer storage and permanent land subsidence, is correlated with CVP and SWP deliveries, and specifically with higher groundwater storage loss during severe drought years. Another key assumption is that the same rates of subsidence will continue even after groundwater levels decline and extraction may be coming from deeper parts of the aquifer system. If the geology and/or aquifer properties change dramatically in response, then these new conditions may have an unmodeled impact on future rates. 

Projected 21st Century Coastal Flooding in the Southern California Bight. Part 2: Tools for Assessing Climate Change-Driven Coastal Hazards and Socio-Economic Impacts

Journal of Marine Science and Engineering (MDPI) | July 2nd, 2018

This paper is the second of two that describes the Coastal Storm Modeling System (CoSMoS) approach for quantifying physical hazards and socio-economic hazard exposure in

This paper is the second of two that describes the Coastal Storm Modeling System (CoSMoS) approach for quantifying physical hazards and socio-economic hazard exposure in coastal zones affected by sea-level rise and changing coastal storms. The modelling approach, presented in Part 1, downscales atmospheric global-scale projections to local scale coastal flood impacts by deterministically computing the combined hazards of sea-level rise, waves, storm surges, astronomic tides, fluvial discharges, and changes in shoreline positions. The method is demonstrated through an application to Southern California, United States, where the shoreline is a mix of bluffs, beaches, highly managed coastal communities, and infrastructure of high economic value. Results show that inclusion of 100-year projected coastal storms will increase flooding by 9–350% (an additional average 53.0 16.0 km2) in addition to a 25–500 cm sea-level rise. The greater flooding extents translate to a 55–110% increase in residential impact and a 40–90% increase in building replacement costs. To communicate hazards and ranges in socio-economic exposures to these hazards, a set of tools were collaboratively designed and tested with stakeholders and policy-makers; these tools consist of two web-based mapping and analytic applications as well as virtual reality visualizations. To reach a larger audience and enhance usability of the data, outreach and engagement included workshop-style trainings for targeted end-users and innovative applications of the virtual reality visualizations.