Colorado River Accounting and Water Use Report: Arizona, California, and Nevada

U.S. Bureau of Reclamation (USBR) | May 15th, 2024

In accordance with Article V of the Consolidated Decree of the United States Supreme Court in Arizona v. California et al. 547 U.S. 150 (2006) (Consolidated Decree): �

In accordance with Article V of the Consolidated Decree of the United States Supreme Court in Arizona v. California et al. 547 U.S. 150 (2006) (Consolidated Decree): “The United States shall prepare and maintain, or provide for the preparation and maintenance of, and shall make available, annually and at such shorter intervals as the Secretary of the Interior shall deem necessary or advisable, for inspection by interested persons at all reasonable times and at a reasonable place or places, complete, detailed and accurate records of: (A) Releases of water through regulatory structures controlled by the United States; (B) Diversions of water from the mainstream, return flow of such water to the stream as is available for consumptive use in the United States or in satisfaction of the Mexican Treaty obligation, and consumptive use of such water. These quantities shall be stated separately as to each diverter from the mainstream, each point of diversion, and each of the States of Arizona, California and Nevada; (C) Releases of mainstream water pursuant to orders therefor but not diverted by the party ordering the same, and the quantity of such water delivered to Mexico in satisfaction of the Mexican Treaty or diverted by others in satisfaction of rights decreed herein. These quantities shall be stated separately as to each diverter from the mainstream, each point of diversion, and each of the States of Arizona, California and Nevada; (D) Deliveries to Mexico of water in satisfaction of the obligations of Part III of the Treaty of February 3, 1944, and, separately stated, water passing to Mexico in excess of treaty requirements; (E) Diversions of water from the mainstream of the Gila and San Francisco Rivers and the consumptive use of such water, for the benefit of the Gila National Forest.” This Colorado River Accounting and Water Use Report: Arizona, California, and Nevada presents the records compiled pursuant to the Consolidated Decree for Calendar Year 2023. Copies of this and previous years’ reports may be found on the Bureau of Reclamation’s website.

Colorado River flow dwindles as warming-driven loss of reflective snow energizes evaporation

American Association for the Advancement of Science (AAAS) | February 20th, 2020

The sensitivity of river discharge to climate-system warming is highly uncertain and governing processes are poorly understood, impeding climate-change adaptation. A prom

The sensitivity of river discharge to climate-system warming is highly uncertain and governing processes are poorly understood, impeding climate-change adaptation. A prominent exemplar is the Colorado River, where meteorological drought and warming have been shrinking a water resource that supports more than US$1 trillion per year of economic activity. Monte-Carlo simulation with a radiation-aware hydrologic model resolves the longstanding, wide disparity in sensitivity estimates and reveals the controlling physical processes. We estimate that annual-mean discharge has been decreasing by 9.3% per °C of warming due to increased evapotranspiration, mainly driven by snow loss and consequent decrease of reflection of solar radiation. Projected precipitation increases likely will not suffice to counter fully the robust, thermodynamically induced drying. Increasing risk of severe water shortages is expected.

Combined Modeling of US Fluvial, Pluvial, and Coastal Flood Hazard Under Current and Future Climates

American Geophysical Union (AGU) | December 16th, 2020

Community estimate of global glacier mass changes from 2000 to 2023

Nature Portfolio (Springer Nature) | February 19th, 2025

Glaciers are indicators of ongoing anthropogenic climate change1. Their melting leads to increased local geohazards2, and impacts marine3 and terrestrial4,5 ecosystems, r

Glaciers are indicators of ongoing anthropogenic climate change1. Their melting leads to increased local geohazards2, and impacts marine3 and terrestrial4,5 ecosystems, regional freshwater resources6, and both global water and energy cycles7,8. Together with the Greenland and Antarctic ice sheets, glaciers are essential drivers of present9,10 and future11,12,13 sea-level rise. Previous assessments of global glacier mass changes have been hampered by spatial and temporal limitations and the heterogeneity of existing data series14,15,16. Here we show in an intercomparison exercise that glaciers worldwide lost 273 ± 16 gigatonnes in mass annually from 2000 to 2023, with an increase of 36 ± 10% from the first (2000–2011) to the second (2012–2023) half of the period. Since 2000, glaciers have lost between 2% and 39% of their ice regionally and about 5% globally. Glacier mass loss is about 18% larger than the loss from the Greenland Ice Sheet and more than twice that from the Antarctic Ice Sheet17. Our results arise from a scientific community effort to collect, homogenize, combine and analyse glacier mass changes from in situ and remote-sensing observations. Although our estimates are in agreement with findings from previous assessments14,15,16 at a global scale, we found some large regional deviations owing to systematic differences among observation methods. Our results provide a refined baseline for better understanding observational differences and for calibrating model ensembles12,16,18, which will help to narrow projection uncertainty for the twenty-first century11,12,18. Click here for more about the Glacier Mass Balance Intercomparison Exercise 

Community Perspectives and Environmental Justice in California's San Joaquin Valley

University of California, Merced | December 1st, 2022

Concepts and evolution of urban hydrology

Nature Portfolio (Springer Nature) | October 24th, 2024

Connecting the dots between water, energy, food, and ecosystems issues for Integrated Water Management in a changing climate

California Department of Water Resources (DWR) | March 7th, 2017

Global climate change creates critical challenges through increasing temperature, reducing snowpack, and changing precipitation for water, energy, and food, as well as fo

Global climate change creates critical challenges through increasing temperature, reducing snowpack, and changing precipitation for water, energy, and food, as well as for ecosystem processes at a regional scale. The water, energy, and food (WEF) nexus and related ecosystems have complex linkages with climate change implications. The overall objectives of this white paper are to provide background on this important subject, and help local water managers and the public better understand: *The ecosystem services for water, energy, and food in a changing climate. *The water-energy nexus and related climate change mitigation actions in California. *The energy used in California’s water sector and estimates of the energy intensity of regional water supplies. Particularly, this paper largely consolidates the water-energy content originally published in California Water Plan Update 2013 (Volumes I, II, and III), which included: *A framework for the energy intensity of California water systems. *An estimate of the regional energy intensity of water supplies. *Water-energy related climate change mitigation policies and actions. *Climate change mitigation benefits and tradeoffs associated with each of the 30 Resource Management Strategies found in Volume III. Furthermore, this paper will explore how water, energy, food, and climate change are interconnected with ecosystems, and why we need to understand these connections and identify the information gaps and related challenges and opportunities for ecosystem services in multiple sectors. Ecosystem services provide life support, goods, and natural resources in water, energy, and food, as well as environments. These are knowledge gaps for lack of conceptual framework and practices to interlink major climate change drivers of water resources with water-energy-food nexus and related ecosystem processes. This white paper provides information review and a conceptual framework to bridge these knowledge gaps. The case studies summarized in this paper indicate there is a large variation in energy intensities for groundwater and federal, state, and local water supplies, both within each hydrological region and among the 10 hydrological regions in California. Regional decisions were critically important in addressing water-energy conflicts and meeting local climate change challenges. These examples can be applicable for the United States and other countries with similar climate change challenges that use diversity of regional water resources for energy and food production. Future interdisciplinary research and support could bridge information and data gaps that are important for using best management practices to obtain efficiency of water, energy, and food systems related to climate change. The increased regional temperature, changes in snowpack and precipitation, and increased water stresses from drought can reduce ecosystem services and affect the water and energy nexus, agricultural food production, and fish and wildlife habitats in California. Regional decisions and practices in integrated management of water, energy, food, and related ecosystem processes are essential to adapting to and mitigating global climate change effects. Science and policy support for interdisciplinary research are critical in developing databases and tools for comprehensive analysis to fill knowledge gaps and address ecosystem service complexity, related natural resource investment, and integrated planning needs. There are significant challenges and opportunities in California to use integrated water management for water, energy, food, and the environment related to climate change. The California Water Action Plan and California Water Plan Update provide a road map and resource management strategies to use integrated water resource management for the multiple benefits of these sectors. The examples and case studies in this white paper have been used to identify information gaps and address related complexity and challenges. Questions posed in this paper regarding water and energy related to the food production cycle need further research and discussion. Overall, we should identify opportunities for innovation and technologies with multiple benefits, evaluate tradeoffs, and address integrated challenges in water, energy, food, and the environment to adapt and mitigate climate change.

Conserving California’s Coastal Habitats: A Legacy and a Future with Sea Level Rise

Nature Conservancy | May 15th, 2018

The California coast that we know today will not be the coast of the future. Sea level rise and other climate change impacts will have profound effects on o

The California coast that we know today will not be the coast of the future. Sea level rise and other climate change impacts will have profound effects on our coastline and its natural resources. California harbors high numbers of native, rare, and imperiled species in an array of unique coastal habitats. A majority of California’s coastline exists as natural habitat, over one-third of which has been preserved by a legacy of conservation efforts. Yet, this conservation legacy is at risk and we must act now to conserve the unique values of California’s coast—for both people and nature—into the future. To inform current and future adaptation decisions and conservation actions we conducted the first statewide, comprehensive assessment of the vulnerability of California’s coastal habitats, imperiled species, and conservation lands to sea level rise. Coastal habitats exist in narrow bands at the land-sea interface and are therefore extremely susceptible to inundation by sea level rise. However, some habitats may be able to adapt vertically and possibly move inland, assuming local topography and the built environment do not constrain this movement. We assessed the vulnerability of 40 habitats to sea level rise by quantifying the sensitivity and spatial extent of projected exposure of each habitat patch to intertidal and subtidal waters, relative to its ability to move inland in response to rising sea levels.

Considerations for Management of the Mouth State of California’s Bar-built Estuaries

Southern California Wetlands Recovery Project | January 10th, 2019

Bar-built estuaries are the dominant estuary type in California, and many of these small estuaries are subject to closure with a sand barrier separating a lagoon

Bar-built estuaries are the dominant estuary type in California, and many of these small estuaries are subject to closure with a sand barrier separating a lagoon estuary from the ocean for days, months or even years. In the lagoon impounded behind the sand barrier, water levels may rise or fall depending on net water budget and water quality extremes may develop. These conditions and the obstruction of fish passage motivate managed breaching of the sand barrier in many systems statewide – an intervention that alleviates or preempts environmental problems, but which also can result in undesirable secondary impacts due to the acute effect of a single breach or the chronic effect of repeated breaching over years. Management decisions are based on an implicit trade-off between anticipated benefits and costs that depend on the values and priorities of stakeholders. This report was written to provide an overview of considerations for managed breaching in California. It presents a synthesis of processes and phenomena related to mouth closure and breaching in general and uses this to identify potential impacts of breaching, without intending any judgment of which impacts are more or less desirable. Three specific systems are reviewed in detail: Los Peñasquitos Lagoon in San Diego County, Scott Creek Estuary in San Mateo County and Russian River Estuary in Sonoma County. While there are fundamental similarities in the closure and breaching cycle across all bar-built estuaries statewide, there is also an immense diversity between these systems due to differences in size, in hydrology (wet north to dry south), and in development (rural, urban, agricultural, road/rail). The local community is likely to develop the best management strategy where there is significant effort and experience in local monitoring, science, and stakeholder consultation. However, where there is limited monitoring, science or consultation, the considerations outlined in this report provide preliminary guidance – and comparison with one of the study systems can provide more specific insight to the potential impacts of breaching management decisions. We synthesize current understanding related to how mouth state influences estuary functions and conditions, which in turn affect ecological services. While both natural and managed breaching affect many processes and phenomena in the estuary, breaching events and managed breaching regimes do not occur in isolation and many other factors affect the estuary functions and conditions, including freshwater inputs, the adjacent landscape, and stressors in the watershed. However, managed breaching is one of very few short-term management options and therefore a valuable adaptive management tool, specifically in systems that are already perturbed or impacted by human encroachment. Although emergency breaches may be required in rare occasions, our recommendation is to develop a breaching strategy for specific systems in which breaching has been used or in which it is likely to be used as a management tool. In this context, we recommend ways in which science can provide improved support for management decisions and identify a few systems in California in which there is already a well-developed, science-based management plan. Associated document: "Wetlands on the Edge: The Future of Southern California's Wetlands - Regional Strategy 2018"

Considerations for Selecting Climate Projections for Water Resources, Planning, and Environmental Analyses

U.S. Bureau of Reclamation (USBR) | March 2nd, 2016

For over a century, Reclamation’s mission has focused on managing water resources in the Western United States. Water resources, planning, and environmental studies car

For over a century, Reclamation’s mission has focused on managing water resources in the Western United States. Water resources, planning, and environmental studies carried out to support Reclamation’s mission have routinely considered hydrologic variability, including variability of water supplies and demands from season to season and year to year. Because weather and climate are two of the primary drivers of water supply and demand, Reclamation studies have also routinely considered weather and climate variability. The SECURE Water Act directs Reclamation to evaluate the risks and impacts of climate change in long-range planning and decision making (see Section 1.1. of the main report), including: •Water resources and environmental analyses •Planning studies •Design and analysis of current and proposed infrastructure and operating plans Considering climate change involves analyzing projected changes in weather and climate conditions as well as the effects of these changes on water supplies, demands, and management.  This document provides an overview of the primary considerations relevant to selecting climate projection information for use in a given water resources, planning, or environmental analysis. Audience For technical specialists involved in selecting and using climate projections for a given study—e.g., climatologist, hydrologists, and water resources engineers— this document provides a brief overview of the models and methods used to develop climate projections (Section 2.) and relevant considerations for selecting an appropriate climate projection dataset and set of climate projections to meet their specific study objectives (Section 3.). This document also provides a detailed summary of available climate projection datasets (Section 4.) and established methods for selecting climate projections for use in a detailed analysis (Section 5.). For other study team members involved in interpreting and documenting the use of climate change information in a given study—e.g., planners, environmental specialists, and resource managers—this document provides an overview of how climate projections are developed (Section 2.) and the choices and considerations involved in selecting climate projections for analysis in the study (Section 3.).