Trends in Snowfall versus Rainfall in the Western United States

American Meteorological Society (AMS) | September 15th, 2006

The water resources of the western United States depend heavily on snowpack to store part of the wintertime precipitation into the drier summer months. A well-documented

The water resources of the western United States depend heavily on snowpack to store part of the wintertime precipitation into the drier summer months. A well-documented shift toward earlier runoff in recent decades has been attributed to 1) more precipitation falling as rain instead of snow and 2) earlier snowmelt. The present study addresses the former, documenting a regional trend toward smaller ratios of winter-total snowfall water equivalent (SFE) to winter-total precipitation (P) during the period 1949–2004. The trends toward reduced SFE are a response to warming across the region, with the most significant reductions occurring where winter wet-day minimum temperatures, averaged over the study period, were warmer than 5°C. Most SFE reductions were associated with winter wet-day temperature increases between 0° and 3°C over the study period. Warmings larger than this occurred mainly at sites where the mean temperatures were cool enough that the precipitation form was less susceptible to warming trends. The trends toward reduced SFE/P ratios were most pronounced in March regionwide and in January near the West Coast, corresponding to widespread warming in these months. While mean temperatures in March were sufficiently high to allow the warming trend to produce SFE/P declines across the study region, mean January temperatures were cooler, with the result that January SFE/P impacts were restricted to the lower elevations near the West Coast. Extending the analysis back to 1920 shows that although the trends presented here may be partially attributable to interdecadal climate variability associated with the Pacific decadal oscillation, they also appear to result from still longer-term climate shifts.

Trends in tree cover change over three decades related to interannual climate variability and wildfire in California

Institute of Physics (IOP) | January 19th, 2025

The U.S. State of California has experienced frequent drought events, hotter temperatures and other disruptions to the climate system whose effects on ecosystems have bee

The U.S. State of California has experienced frequent drought events, hotter temperatures and other disruptions to the climate system whose effects on ecosystems have been widely reported in recent decades. Studies primarily confined to specific vegetation communities or species, individual drought incidents, or analysis over a relatively short intervals, has limited our understanding of the broad-scale effects on tree cover and the spatiotemporal variability of effects across broader regions. We focused analysis on multi-annual land cover and land surface change to assess patterns and trends in tree cover loss in tree-dominated Californian ecoregions from 1986 to 2019. The top three years of total tree cover loss for the state were 2018 (1901 km2), 2015 (1556 km2), and 2008 (1549 km2). Overall, annual tree cover loss had upward trends. Tree cover loss rapidly surged later in the study period and was apparently driven by climate stress and wildfires. Underlying geographic variability was apparent in both non-fire and fire-related tree cover loss that sharply increased during hotter multi-year droughts. The increasingly hotter and drier climate conditions were associated with significant increases in fire-induced mortality. Our findings indicate that a possible effect of future hotter and drier climate would lead to further tree cover loss, thereby endangering California's ecosystem goods and services. Geographic variability in tree cover trends indicates that ecoregion-specific mitigation and adaptation strategies would be useful to conserve the region's forest resources. Such strategies may benefit from consideration of historical disturbances, ecoregion's sensitivity to disturbance types, as well as potential ecoregion-specific climate-vegetation-fire feedbacks.

Tri-County Water Authority Groundwater Sustainability Plan

Tri-County Water Authority | December 18th, 2019

Tribal Collaboration in IRWM: Challenges, Solutions and Recommendations

University of California, Davis (UC Davis) | May 5th, 2017

The Integrated Regional Water Management (IRWM) Tribal Collaborative Effectiveness Study evaluates Tribal participation in the Department of Water Resources’ (DWR) Inte

The Integrated Regional Water Management (IRWM) Tribal Collaborative Effectiveness Study evaluates Tribal participation in the Department of Water Resources’ (DWR) Integrated Regional Water Management (IRWM) grant program.  The Department administers the overall IRWM program, and individual regions form Regional Water Management Groups (RWMG) develop IRWM plans and submit specific water management projects for funding consideration by DWR. Following indigenous collaborative research protocols, we conducted surveys, interviews and focus-group meetings with Tribal representatives throughout the state. While we collected data from Tribes statewide, our efforts were focused in five specific IRWM regions. The aim of our research is to identify strengths, weaknesses, and opportunities for Tribal participation in the IRWM program.

Tribal Communication Plan

California Department of Water Resources (DWR) | June 1st, 2008

Tribal environmental and natural resource assistance handbook

U.S. Environmental Protection Agency (EPA) | March 11th, 1999

This handbook was developed by the Domestic Policy Council Working Group on American Indians and Alaska Natives (Working Group). The first draft of this document was poss

This handbook was developed by the Domestic Policy Council Working Group on American Indians and Alaska Natives (Working Group). The first draft of this document was possible thanks to the significant contributions of the Native American Fish & Wildlife Society. Previous drafts of the handbook were reviewed by each federal contributor and also went through the interagency review process at the Office of Management and Budget. The result is a compilation of the federal sources of financial and/or technical assistance programs available for Tribal environmental management. The handbook is intended to provide a central location for federal sources of both technical and financial assistance available to Tribes for environmental management. Many Tribes have limited environmental staffs that are faced with the challenge of addressing a broad range of environmental issues. Unlike State environmental programs that have received annual federal funding for many years, Tribal environmental programs generally must compete annually for their funds. With 554 federally recognized Tribes, there simply is not enough money to go around. Therefore, Tribal environmental staffs spend a large part of their time applying for grants and searching for sources of federal assistance. This document is an effort to assist Tribal staff in their search and hopefully save them valuable time. The handbook can also assist federal, regional, State and Local government employees in becoming better informed about the sources of environmental assistance available in order to improve customer service to the Tribes. The Working Group recognizes that this document does not contain every federal resource available to Tribes. This is an evolving document and will be updated periodically. Future versions of this document will be available on the Internet (see Comments section).

Tribal Water Study: An Overview

Water and Tribes Initiative | October 28th, 2019

The purpose of this policy brief is to provide an overview of the Colorado River Basin Ten Tribes Partnership Tribal Water Study (Study), a unique review of the water rig

The purpose of this policy brief is to provide an overview of the Colorado River Basin Ten Tribes Partnership Tribal Water Study (Study), a unique review of the water rights, water uses, and future plans of the member tribes of the Colorado River Basin Tribes Partnership (Ten Tribes Partnership). The information in this policy brief is taken directly from the Study. In the foreword to the Study, Bureau of Reclamation (Reclamation) Commissioner Brenda Burman states that Reclamation and the Ten Tribes Partnership collaborated to document current water use and potential future water development to better facilitate planning and decision-making throughout the Colorado River Basin (Basin). The Study strengthens a Department of the Interior commitment to address water issues facing tribes and recognizes that the Colorado River is an essential foundation for the physical, economic, and cultural sustenance of tribes in the Basin. The Study also explores ways to provide a wide range of benefits to both Partnership Tribes and other water users. The mutual trust and understanding forged during the Study will prove to be critical as the Basin collaboratively addresses the significant challenges ahead. The Ten Tribes Partnership, in its foreword, stated that in addition to producing technical information, the Tribes had other goals. First, they wanted to better understand how, at present, the Study’s water use scenarios fit into the overall scheme of Colorado River Basin management. Second, they wanted to know how future development of tribal water resources will affect other water users who are now using water to which a tribe may hold legal title, but which the title-holding tribe has not yet developed for its own use. Finally, they wanted to assess--to the extent present information allows -- the role future development of tribal water rights will have on Basin operations. The Ten Tribes Partnership hopes the Study resolves some uncertainty about how tribes perceive the future for their water uses, and establishes a baseline of information for discussions and development of relationships among tribes, states, federal government, water managers, and water users throughout the Basin.

Tribal Water Summit Proceedings: California Indigenous Rights, Uses, and Management of Land and Water (2013)

California Department of Water Resources (DWR) | March 26th, 2014

Two hundred representatives from California Native American Tribes, Federal and State agencies, and Native American organizations participated in the 2013 California Trib

Two hundred representatives from California Native American Tribes, Federal and State agencies, and Native American organizations participated in the 2013 California Tribal Water Summit. This event continued key concepts discussed at the 2009 Tribal Water Summit: »» Tribal Ecological Knowledge (TEK) – emphasizing greater respect for, and understanding of, Tribal knowledge and its value in resource management; »» Indigenous Rights to Water – focusing on the broader context and relationships between Tribes and water; and »»Watershed Management and Land Use – looking at the integration of TEK and indigenous water rights with local, regional and statewide watershed efforts and projects which affect Tribal communities, trust lands and homelands. Three plenary speakers were featured during the Summit. On the first day, Heather Whiteman Runs Him, Staff Attorney for the Native American Rights Fund, discussed Tribal water rights principles and approaches. On the second day, Felicia Marcus, Board Chair for the State Water Board, reflected on the importance of establishing and maintaining relationships between agencies and Tribes. Also on the second day, Cynthia Gomez, Tribal Advisor to the Governor, provided an overview on the work of the Tribal Advisor’s Office. On Day 1, opening remarks were offered by John Laird, Secretary for the California Natural Resources Agency, and Dale Hoffman-Floerke, Chief Deputy Director for the California Department of Water Resources (DWR).   Mr. Laird highlighted the efforts within the Resources Agency to better balance historic rights with multiple needs and interests. He shared the experiences from the MLPA Initiative, and described the adoption of the Tribal consultation policy and creation of the Tribal liaison positions. Ms. Hoffman-Floerke called attention to the TWS Guiding Principles and Statement of Goals for Implementation, which are supported by the Resources Agency and DWR. She described the 2013 TWS as succession planning, which supports the continuity of awareness, understanding and relationships from the 2009 TWS.

Tribal-Traditional Ecological Knowledge and the Use of Fire

California Department of Water Resources (DWR) | September 9th, 2014

A memo written by Ron W. Goode, Tribal Chairman, North Fork Mono Tribe on Traditional Ecological Knowledge and the use of fire.  This document was part of the reference

A memo written by Ron W. Goode, Tribal Chairman, North Fork Mono Tribe on Traditional Ecological Knowledge and the use of fire.  This document was part of the reference documents included with the California Water Plan 2013 Update.

Tritium as an indicator of modern, mixed, and premodern groundwater age

U.S. Geological Survey (USGS) | September 4th, 2019

Categorical classification of groundwater age is often used for the assessment and understanding of groundwater resources. This report presents a tritium-based age classi

Categorical classification of groundwater age is often used for the assessment and understanding of groundwater resources. This report presents a tritium-based age classification system for the conterminous United States based on tritium (3H) thresholds that vary in space and time: modern (recharged in 1953 or later), if the measured value is larger than an upper threshold; premodern (recharged prior to 1953) if the measured value is smaller than a lower threshold; or mixed if the measured value is between the two thresholds. Inclusion of spatially varying thresholds, rather than a single threshold, accounts for the observed systematic variation in 3H deposition across the United States. Inclusion of time-varying thresholds, rather than a single threshold, accounts for the date of sampling given the radioactive decay of 3H. The efficacy of the tritium-based age classification system was evaluated at national and regional scales. The system was evaluated at a national scale by classifying samples from 1,788 public-supply wells distributed across 19 principal aquifers and comparing those results with expectations based on hydrogeologic principles. The regional-scale data are from five paired networks of shallow and deep wells (287 wells). As expected, modern groundwater is more prevalent in shallow wells than in deeper wells, in fractured-rock and carbonate aquifers as compared to clastic aquifers, in unconfined areas as compared to confined areas, and in humid climates as compared to arid climates. The results from a tritium-based age classification system compared favorably with the results of 14 previous studies of groundwater ages that used different age tracers and analytical methods. The wells and samples from the Cambrian-Ordovician aquifer that had been analyzed using a more complex multi-tracer analysis were also analyzed using the tritium-based age classification system, and there was a close match between the two methods. The results from these various studies suggest that the tritium-based age classification system may be informative as a screening tool prior to selecting more expensive and complex age-dating tracers and methods, or to provide an explanatory variable for other water-quality data where more complex methods or tracers are not available. This work improves on previous groundwater age classification using 3H by developing methods that (1) determine 3H thresholds for groundwater recharged in 1953 or later that minimize the misclassification of modern samples as mixed; (2) determine a pre-1953 threshold to estimate premodern background concentrations; and (3) add a mixed category to classify samples that are clearly neither entirely modern nor entirely premodern. As with any tritium-based approach, it can fail when the 3H record in precipitation does not accurately reflect the record of 3H in recharge