Paradise Regained: Solution for restoring Yosemite's Hetch Hetchy Valley

Environmental Defense Fund (EDF) | July 15th, 2004

In this report Environmental Defense provides a planning-level analysis for replacing the water and hydropower benefits that the Hetch Hetchy Reservoir and O’Shaughness

In this report Environmental Defense provides a planning-level analysis for replacing the water and hydropower benefits that the Hetch Hetchy Reservoir and O’Shaughnessy Dam provide.We show how practical, proven water storage, conveyance and treatment alternatives can provide San Francisco a healthy, reliable and secure supply of water that is adequate for current and future needs.  We also explain how hydropower lost as a result of restoring the valley can be replaced without contributing to air pollution or global warming. The alternatives analyzed do not comprise all possible options, but they do demonstrate that workable solutions for restoring Hetch Hetchy Valley exist. We began this study with the premise that all solutions must be technologically feasible and affordable and must assure a dependable supply of safe drinking water. In addition to addressing the water and power needs of San Francisco and other Bay Area communities that rely on the Tuolumne River, solutions must also protect all affected California communities. Most obviously, any restoration plan must protect the Turlock and Modesto Irrigation Districts, whose uses of the Tuolumne River predate and are intertwined with those of the San Francisco Public Utilities Commission (SFPUC) and its customers. Of course, a restoration plan must also consider the Groveland area, both as a user of the Tuolumne River water and as a gateway community to the Hetch Hetchy region of Yosemite National Park. Our analysis focuses mainly on alternative ways to move and store San Francisco’s existing supply of Tuolumne River water. Environmental Defense developed the TREWSSIM (Tuolumne River Equivalent Water Supply Simulation) model to evaluate the SFPUC’s system performance under a range of water supply alternatives, with and without Hetch Hetchy Reservoir.TREWSSIM incorporates features of both the SFPUC’s planning model HHSM-LSM and the state-federal CALSIM model. The TREWSSIM analysis addresses not only water supply issues, but also water treatment and hydropower. Three expert consultants assisted in our analysis: Schlumberger Water Services provided engineering analyses and modeling assistance; Eisenberg, Olivieri and Associates analyzed water quality issues; and Somach, Simmons  & Dunn assessed the legal landscape. Academic experts provided peer review. The San Francisco Public Utilities Commission, the Bay Area Water Supply and Conservation Agency, and the Turlock and Modesto Irrigation Districts also provided information to help ensure an accurate report.

Paso Robles vineyard irrigation study provides benchmark data to assist future area groundwater management

California Agriculture (UCANR) | March 13th, 2018

Accurate information on irrigation water usage does not exist in many areas where groundwater is the primary water source. This lack of information will hinder

Accurate information on irrigation water usage does not exist in many areas where groundwater is the primary water source. This lack of information will hinder efforts to manage these groundwater basins sustainably according to current and future water regulations and policies. Using a low-cost methodology of irrigation-line pressure sensors connected to data loggers, we estimated irrigation applications at 84 vineyard sites in the Paso Robles Groundwater Basin over 4 years (2010–2013). We compared irrigation amounts with the preceding winter’s rainfall and with the growing season reference evapotranspiration (ETo). Over the study period, the average annual irrigation application was 11.46 inches (291 millimeters). The average annual application correlated inversely to the preceding winter’s rainfall, while the irrigation over the growing season (April–October) correlated directly with the ETo over this same period. This study provides an initial data framework that can be used by groundwater sustainability agencies to help manage groundwater in the Paso Robles area. The methodology also could be utilized in other regions to estimate regional irrigation usage while maintaining anonymity for participants.

Patterns and magnitude of flow alteration in California, USA

Freshwater Biology (Wiley) | December 27th, 2017

The importance of the natural flow regime to stream and river health has received growing attention over the last two decades. Quantifying natural river flows has become

The importance of the natural flow regime to stream and river health has received growing attention over the last two decades. Quantifying natural river flows has become an essential component of water resource planning, including assessments of water supplies (Vicuna,Maurer, Joyce, Dracup, & Purkey, 2007; Wurbs, 2005), reservoir operations (Hejazi, Cai, & Ruddell, 2008) and drought risk (Meko,Therrell, Baisan, & Hughes, 2001). Understanding the natural flow regime is also crucial for managing stream ecosystems.

Perspectives and Guidance for Climate Change Analysis

California Department of Water Resources (DWR) | August 14th, 2015

California's water managers face a climate that changes and is changing as a result of both natural and anthropogenic influences. In some settings and for some variables,

California's water managers face a climate that changes and is changing as a result of both natural and anthropogenic influences. In some settings and for some variables, California’s natural climate variability still dominates anthropogenic influences and will continue to do so for the foreseeable future. In other cases, anthropogenic influences are already evident in important aspects of California's climate. Much research is still required to unravel this tangled web of atmospheric interactions. In any case, California water planning under a changing climate needs to recognize that the causes of variations and changes include both anthropogenic and natural drivers. This technical information record summarizes the scientific and technical guidance and perspectives of the California Department of Water Resources’ (DWR’s) Climate Change Technical Advisory Group (CCTAG) on the use of climate models and associated technical tools for water resource planning. DWR values the work of the members of the CCTAG and will consider this advice as it moves forward in developing specific actions. DWR empaneled this CCTAG in February 2012 to advise DWR on the scientific aspects of climate change, its impacts on water resources, the use of planning approaches and analytical tools, and the development of adaptation responses. DWR requested specific assistance with developing: • A set of future climate scenarios and analysis procedures appropriate for DWR planning. • An approach to extreme climate change scenarios to provide “stress tests.” • Interim guidance on modeling extreme weather events that cause flooding (time permitting within the tenure of the CCTAG).

Planned operation of large-scale water-distribution system

American Society of Civil Engineers (ASCE) | May 1st, 1995

A water-supply-distribution-system planning model has been developed using a directed graph algorithm as its pre- and post-processors and a linear programming (LP) proced

A water-supply-distribution-system planning model has been developed using a directed graph algorithm as its pre- and post-processors and a linear programming (LP) procedure as an “intelligent” system operator at its core. The directed graph, as a preprocessor, is used to produce a mathematical representation of the distribution system in question, to check the consistency and correctness of the network topology before an input file is created for the LP procedure. In the postprocessing mode, the directed graph generates files for graphical displays of model results and performs graph analyses such as depth- and breadth-first traversals, cut-set and connectivity for evaluating water-quality blending, tracking of source-to-demand contributions, system reliability, and lifeline objectives. Unlike the conventional formulation of a resource-allocation problem, the demand requirements, storage capacities, and other system constraints are removed from the constraint set and translated into a composite objective function. This methodology was successfully applied to the Metropolitan Water District of Southern California's (MWD's) distribution system. The results indicate that the combination of using an LP procedure and graph algorithm is a very versatile tool for solving large-scale water-distribution problems. This paper documents the concept used in developing the system-planning model and the results of its application to a simplified example as well as application to four case studies involving the entire MWD's distribution system.

Poleward shift of the major ocean gyres detected in a warming climate

American Geophysical Union (AGU) | February 24th, 2020

Recent evidence shows that wind‐driven ocean currents, like the western boundary currents, are strongly affected by global warming. However, due to insufficient observa

Recent evidence shows that wind‐driven ocean currents, like the western boundary currents, are strongly affected by global warming. However, due to insufficient observations both on temporal and spatial scales, the impact of climate change on large‐scale ocean gyres is still not clear. Here, based on satellite observations of sea surface height and sea surface temperature, we find a consistent poleward shift of the major ocean gyres. Due to strong natural variability, most of the observed ocean gyre shifts are not statistically significant, implying that natural variations may contribute to the observed trends. However, climate model simulations forced with increasing greenhouse gases suggest that the observed shift is most likely to be a response of global warming. The displacement of ocean gyres, which is coupled with the poleward shift of extratropical atmospheric circulation, has broad impacts on ocean heat transport, regional sea level rise and coastal ocean circulation.

Post-Drought Groundwater Storage Recovery in California's Central Valley

American Geophysical Union (AGU) | October 5th, 2021

California's Central Valley has experienced chronic groundwater depletion over the past few decades, the rate of which was amplified by droughts in 2007–2009 and 2012�

California's Central Valley has experienced chronic groundwater depletion over the past few decades, the rate of which was amplified by droughts in 2007–2009 and 2012–2016. There is limited knowledge as to how much of the drought-caused groundwater depletion has recovered during post-drought years and how climate and water management affect overdraft recovery times. We address these issues by estimating groundwater storage changes using four methods and conducting numerical experiments with varying climatic conditions and water management options. We find that less than one-third of the groundwater overdraft from the most recent droughts was recovered during post-drought years. Projected overdraft recovery times vary greatly depending on the climate scenarios and water management strategies, and future droughts are likely to cause overdrafts from which recovery is unlikely given the current level of groundwater extractions. However, management measures such as capping groundwater pumping could reduce recovery times by a factor of two or more depending on the groundwater extraction cap and post-drought climate.

Potential impacts of increased coastal flooding in California due to sea-level rise

Climatic Change (Springer) | November 24th, 2011

California is likely to experience increased coastal flooding and erosion caused by sea-level rise over the next century, affecting the state’s population, infrastructu

California is likely to experience increased coastal flooding and erosion caused by sea-level rise over the next century, affecting the state’s population, infrastructure, and environment. As part of a set of studies on climate change impacts to California, this paper analyzes the potential impacts from projected sea-level rise if no actions are taken to protect the coast (a “no-adaptation scenario”), focusing on impacts to the state’s population and infrastructure. Heberger et al. (2009) also covered effects on wetlands, costs of coastal defenses, and social and environmental justice related to sea-level rise. We analyzed the effect of a medium-high greenhouse gas emissions scenario (Special Report on Emissions Scenarios A2 in IPCC 2000) and included updated projections of sea-level rise based on work by Rahmstorf (Science 315(5810): 368, 2007). Under this scenario, sea levels rise by 1.4 m by the year 2100, far exceeding historical observed water level increases. By the end of this century, coastal flooding would, under this scenario, threaten regions that currently are home to approximately 480,000 people and $100 billion worth of property. Among those especially vulnerable are large numbers of low-income people and communities of color. A wide range of critical infrastructure, such as roads, hospitals, schools, emergency facilities, wastewater treatment plants, and power plants will also be at risk. Sea-level rise will inevitably change the character of California’s coast; practices and policies should be put in place to mitigate the potentially costly and life-threatening impacts of sea-level rise.

Potential Impacts of Reduced Inflows to the Salton Sea: Forecasting Non-market Damages

American Water Resources Association (AWRA) | September 28th, 2022

Precipitation in a warming world: Assessing projected hydro-climate changes in California and other Mediterranean climate regions

Nature Portfolio (Springer Nature) | September 7th, 2017

In most Mediterranean climate (MedClim) regions around the world, global climate models (GCMs) consistently project drier futures. In California, however, proj

In most Mediterranean climate (MedClim) regions around the world, global climate models (GCMs) consistently project drier futures. In California, however, projections of changes in annual precipitation are inconsistent. Analysis of daily precipitation in 30 GCMs reveals patterns in projected hydrometeorology over each of the five MedClm regions globally and helps disentangle their causes. MedClim regions, except California, are expected to dry via decreased frequency of winter precipitation. Frequencies of extreme precipitation, however, are projected to increase over the two MedClim regions of the Northern Hemisphere where projected warming is strongest. The increase in heavy and extreme precipitation is particularly robust over California, where it is only partially offset by projected decreases in low-medium intensity precipitation. Over the Mediterranean Basin, however, losses from decreasing frequency of low-medium-intensity precipitation are projected to dominate gains from intensifying projected extreme precipitation. MedClim regions are projected to become more sub-tropical, i.e. made dryer via pole-ward expanding subtropical subsidence. California’s more nuanced hydrological future reflects a precarious balance between the expanding subtropical high from the south and the south-eastward extending Aleutian low from the north-west. These dynamical mechanisms and thermodynamic moistening of the warming atmosphere result in increased horizontal water vapor transport, bolstering extreme precipitation events.