North Coast

Extreme Precipitation-Temperature Scaling in California: The Role of Atmospheric Rivers

American Geophysical Union (AGU) | July 25th, 2023

Faster, bigger, more severe: Extreme wildfire spread sets the stage for forest ecosystem change in western and boreal North America

American Association for the Advancement of Science (AAAS) | August 12th, 2026

A relatively small number of rapidly spreading wildfire events burn disproportionately large areas. But beyond area burned, do fast fires produce distinct postfire ecolog

A relatively small number of rapidly spreading wildfire events burn disproportionately large areas. But beyond area burned, do fast fires produce distinct postfire ecological outcomes? Here, we measure daily linear fire growth rates and assess relationships between fire spread, burn severity, and metrics of postfire landscape resilience from 3499 fires occurring between 2012 and 2023 in conifer-dominated forests of Canada and the western US. We find that as linear spread rate increases, so too does fire severity, proportion of area burned at high severity, and distance to surviving live tree seed sources. Thus, not only do the fastest fires burn outsized areas, but these areas have less remaining tree cover and reduced capacity for recovery, setting the stage for long-term vegetation shifts. Given anticipated increases in extreme fire spread as fire seasons lengthen and weather becomes more fire-conducive, our findings highlight growing needs to effectively reduce undesired impacts, manage postfire landscapes to sustain forest ecosystem functions, and foster social-ecological adaptation.

Final Environmental Impact Report for Adoption of a Regulation for the Hexavalent Chromium Maximum Contaminant Level

California State Water Resources Control Board (SWRCB) | April 17th, 2024

As the lead agency in accordance with sections 15089 and 15132 of the California Environmental Quality Act (CEQA) Guidelines (Cal. Code Regs., tit. 14, § 15000 et seq.),

As the lead agency in accordance with sections 15089 and 15132 of the California Environmental Quality Act (CEQA) Guidelines (Cal. Code Regs., tit. 14, § 15000 et seq.), this document is the Final Environmental Impact Report (Final EIR) for the adoption of statewide regulations setting the maximum contaminant level (MCL) for hexavalent chromium (Proposed Regulations). The Proposed Regulations include a maximum contaminant level (MCL) of 10 μg/L for hexavalent chromium. (Cal. Code Regs. tit. 22, § 64431 Table 64431-A.) The Proposed Regulations also include a compliance schedule based on public water system size, by adding subdivision (p) and Table 64432-B to section 64432 of title 22 of the California Code of Regulations, identifies a detection limit for purposes of reporting, sets monitoring and reporting requirements and public notice requirements for violations of the MCL, and establishes the Best Available Technologies (BAT) for treating hexavalent chromium in drinking water. California State Water Resources Control Board (SWRCB) Chrom VI MCL rulemaking chronology.

Final State Water Project Delivery Capability Report 2023

California Department of Water Resources (DWR) | July 31st, 2024

This Delivery Capability Report presents California Department of Water Resources (DWR) analysis of the State Water Project (SWP) system and provides important planning i

This Delivery Capability Report presents California Department of Water Resources (DWR) analysis of the State Water Project (SWP) system and provides important planning information for users of SWP water. The analysis provides information about how changing climate, regulatory, and operational considerations impact SWP delivery capability.

Fish die-offs are concurrent with thermal extremes in north temperate lakes

Nature Portfolio (Springer Nature) | July 8th, 2019

As environmental temperatures continue to rise and organisms experience novel and potentially lethal conditions, the possibility of increased mass mortality events for an

As environmental temperatures continue to rise and organisms experience novel and potentially lethal conditions, the possibility of increased mass mortality events for animal populations appears likely. Yet, due to die-off rarity and unpredictability, there have been few large-scale attempts to quantify the relationship between mass die-offs and local environmental temperatures. Here, we address this issue by analysing a database of 502 freshwater fish die-offs combined with lake-specific temperature profiles simulated for north temperate lake ecosystems. Die-offs driven by extreme summer conditions occurred disproportionately in lakes with warmer average surface temperatures and during periods of extreme heat. In contrast, we observed no relationships between current thermal extremes and die-offs attributed to infectious disease or winter environmental conditions. We forecast fish die-offs driven by summer environmental conditions to double by mid-century for north temperate lakes (2041–2059) and to increase more than fourfold by late century (2081–2099), particularly at southern latitudes. These results expose a direct link between novel temperature regimes and the increased probability of catastrophic ecological events in freshwater ecosystems.

Fishes, Hydrology, and Ecology of the Klamath River Basin

National Academy of Sciences (NAS) | February 11th, 2008

The Klamath River basin in southern Oregon and northern California is the focus of a prominent conflict over competing uses for water in the American West. Management mea

The Klamath River basin in southern Oregon and northern California is the focus of a prominent conflict over competing uses for water in the American West. Management measures for the protection of threatened and endangered fish species in the basin that have left less water available for irrigation have increased tensions among farmers and other stakeholders and brought into question the scientific justification of these measures. Two National Research Council studies evaluate a series of federal scientific assessments and recommend scientifically justified approaches to the problem.

Flood Size Increases Nonlinearly Across the Western United States in Response to Lower Snow-Precipitation Ratios

American Geophysical Union (AGU) | December 20th, 2019

Many mountainous and high-latitude regions have experienced more precipitation as rain rather than snow due to warmer winter temperatures. Further decreases in the annual

Many mountainous and high-latitude regions have experienced more precipitation as rain rather than snow due to warmer winter temperatures. Further decreases in the annual snow fraction are projected under continued global warming, with potential impacts on flood risk. Here, we quantify the size of streamflow peaks in response to both seasonal and event-specific rain-fraction using stream gage observations from watersheds across the western United States. Across the study watersheds, the largest rainfall-driven streamflow peaks are >2.5 times the size of the largest snowmelt-driven peaks. Using a panel regression analysis of individual precipitation and snowmelt events, we show that the empirical streamflow response grows approximately exponentially as the liquid precipitation input increases, with rain-dominated runoff leading to proportionately larger streamflow increases than snowmelt or mixed rain-and-snow runoff. We find that the response to changes in rain percentage is largest in the wettest watersheds, where wet antecedent conditions are important for increasing runoff efficiency. Similarly, the effect of rain percentage is larger across watersheds in the Northwest and West regions compared to watersheds in the Northern Rockies and Southwest regions. Overall, as a higher percentage of precipitation falls as rain, increases in the size of rainfall-driven and “rain-on-snow”-driven floods have the potential to more than offset decreases in the size of snowmelt-driven floods.

Flood-MAR Research and Data Development Plan

California Department of Water Resources (DWR) | October 31st, 2019

The Research Advisory Committee (RAC) is pleased to make this plan available to the growing network of farmers, researchers, planners, and water and land managers who wan

The Research Advisory Committee (RAC) is pleased to make this plan available to the growing network of farmers, researchers, planners, and water and land managers who want to expand our collective knowledge about using floodwaters for managed aquifer recharge (Flood-MAR). This plan outlines the priority information needed by those making management decisions about the where, when, and how of capturing available flood water to replenish California’s depleted aquifers.

Floods in California

Public Policy Institute of California (PPIC) | February 29th, 2024

Forests and Water in the Sierra Nevada: Sierra Nevada Watershed Ecosystem Enhancement Project

University of California, Merced (UC Merced) | November 21st, 2011

In this white paper on the Sierra Nevada Watershed Ecosystem Enhancement Project (SWEEP), we make the case that upstream management of Sierra Nevada forests can significa

In this white paper on the Sierra Nevada Watershed Ecosystem Enhancement Project (SWEEP), we make the case that upstream management of Sierra Nevada forests can significantly increase the value of downstream water resources by shifting water towards higher value uses and optimizing the timing of runoff. The focus of this paper is on the west-side mixed-conifer forests at elevations of about 1500-3600 m (5000-12,000 ft), which are highly productive owing to the availability of sufficient water, predominance of above-freezing temperatures and presence of other conditions necessary for growth.  California has a Mediterranean climate, with wet winters and dry summers. Precipitation falling as rain on Sierra Nevada forests enters the soil and is partitioned between evapotranspiration and runoff. Much of the rainfall leaves the forest as evapotranspiration, owing to ample water storage in the subsurface and temperatures that allow growth year round. At higher elevations, e.g. above elevations of 1800-2100 m depending on both latitude and microclimate, which are dominated by snow rather than rain, the snowpack provides an important seasonal storage of water that, together with subsurface-water storage, provides the water needed for forest growth over the summer and fall. Forest thinning to reduce vegetation and thus evapotranspiration will result in a higher fraction of precipitation, particularly snowmelt, leaving the mountain forest as runoff. Historically, the unique character of Sierra Nevada forests was defined by its tall trees, relatively mild climate and low forest density. In many areas, current forest densities are much higher than historical values. Forest thinning can also influence the timing of snowmelt and runoff. That is, a less-dense canopy can allow snow to reach the ground rather than be held in the canopy; and strategic spacing of forest openings will limit early season sunlight reaching the forest floor and retard snowmelt.  In this paper we review the forest hydrology literature relevant to management of conifer forests in the Sierra snow zone, as that management affects the timing and amount of snowmelt runoff. In order to understand the conceptual and practical challenges, we summarize the key elements of forest energy budget, with specific reference to the Sierra Nevada, and describe several relevant case studies. Although principles that govern the mountain water cycle are well known and models of water and energy balance are informed by field measurements in some areas, there is a severe knowledge gap that limits quantitative predictions of the effects of forest thinning on Sierra Nevada water and energy cycles. Nevertheless, generalizations from reviews of paired catchment studies carried out elsewhere suggest that Sierra Nevada conifer forests contain ecological attributes with a high potential for water-yield gains. Historical studies of forest harvesting in the Sierra Nevada have shown increases of between 14 and 34% in snow accumulation. Treatments that increase snow accumulation help increase water yield during low flows, when water resources’ economic and ecosystem values are highest.  Preliminary estimates based on average climate information suggest that in the Sierra Nevada, treatments that would reduce forest cover by 40% of maximum levels across a watershed could increase water yields by about 9%. Note that this white paper focused on forest management effects on the water balance. Impacts on wildlife habitat, forest health, and fire behavior were not analyzed. The projections and models reported here are designed to describe the potential for modifying water yield and timing. Before implementation of any strategy, a wider consideration of the consequences on forest structure and function would be necessary.  Because of the potential for water-yield increases and extended snow storage, the SWEEP project has developed a plan to evaluate forest thinning related to water yield in representative headwater catchments in the Sierra Nevada, as a basis for extending these treatments to broader areas of the Sierra Nevada. To that end, we outline an experiment that could be carried out in the Onion Creek Experimental Forest, Tahoe National Forest, Placer County, California that could test silvicultural treatments designed to modify the water balance of mixed-conifer, snow-dominated catchments. The treatments are based on a leaf area index (LAI) approach (O’Hara 1998) to forest management, which is well-suited to water yield and timing objectives. Our initial estimates are that treatments could increase water yield as much as 16% and extend snow storage, i.e. delay snowmelt, by days to weeks.