Quantifying Aspect-Dependent Snowpack Response to High-Elevation Wildfire in the Southern Rocky Mountains

American Geophysical Union (AGU) | September 17th, 2024

Rapid vegetation redistribution in Southern California during the early 2000s drought

American Geophysical Union (AGU) | August 31st, 2012

Climate change in semi-arid, midlatitude mountain environments is expected to shift the spatial patterns of temperature, water availability, and vegetation upslope. Veg

Climate change in semi-arid, midlatitude mountain environments is expected to shift the spatial patterns of temperature, water availability, and vegetation upslope. Vegetation growing near its low-elevation range limit may prove especially vulnerable to mortality and decline. We investigated the altitudinal pattern of conifer mortality that occurred from 2002 to 2004 in Southern California’s San Jacinto Mountains. We found that conifer mortality was focused in the lower portion of the midmontane conifer range, which drove the midmontane conifer distribution upslope. We investigated past reports of conifer mortality in Southern California by searching historical newspaper accounts. We found evidence of previous episodes of conifer mortality that coincided with past droughts, and which may have caused vegetation redistribution in the past. We interpret the early2000s mortality and associated vegetation redistribution as a response to natural decadal tocentennial climate variability. Moreover, we hypothesize this response mode will dominatethe early impact of global climate change on semi-arid forest, which, in turn, may complicate efforts to distinguish between ecological changes attributable to natural climate variability and those attributable to global climate change.

Recent decreases in snow water storage in western North America

Nature Portfolio (Springer Nature) | May 22nd, 2023

Mountain snowpacks act as natural water towers, storing winter precipitation until summer months when downstream water demand is greatest. We introduce a Snow Storage Ind

Mountain snowpacks act as natural water towers, storing winter precipitation until summer months when downstream water demand is greatest. We introduce a Snow Storage Index (SSI), representing the temporal phase difference between daily precipitation and surface water inputs—sum of rainfall and snowmelt into terrestrial systems—weighted by relative magnitudes. Different from snow water equivalent or snow fraction, the SSI represents the degree to which the snowpack delays the timing and magnitude of surface water inputs relative to precipitation, a fundamental component of how snow water storage influences the hydrologic cycle. In western North America, annual SSI has decreased (p 

Reduced resilience as an early warning signal of forest mortality

Nature Portfolio (Springer Nature) | October 7th, 2019

Climate-induced forest mortality is being widely observed across the globe. Predicting forest mortality remains challenging because the physiological mechanisms c

Climate-induced forest mortality is being widely observed across the globe. Predicting forest mortality remains challenging because the physiological mechanisms causing mortality are not fully understood and empirical relations between climatology and mortality are subject to change. Here, we show that the temporal loss of resilience, a phenomenon often detected as a system approaches a tipping point, can be used as an early warning signal (EWS) to predict the likelihood of forest mortality directly from remotely sensed vegetation dynamics. We tested the proposed approach on data from Californian forests and found that the EWS can often be detected before reduced greenness, between 6 to 19 months before mortality. The EWS shows a species-specific relation with mortality, and is able to capture its spatio-temporal variations. These findings highlight the potential for such an EWS to predict forest mortality in the near-term.

Regional patterns and proximal causes of the recent snowpack decline in the Rocky Mountains, U.S.

American Geophysical Union (AGU) | March 30th, 2013

Climatologies of Rocky Mountain snowpack are shown to be seasonally and regionally complex, with Pacific decadal variability positively reinforcing the anthropogenic warm

Climatologies of Rocky Mountain snowpack are shown to be seasonally and regionally complex, with Pacific decadal variability positively reinforcing the anthropogenic warming trend.

Restoration pulse flows from a California dam temporarily increase drifting invertebrate biomass concentration

Journal of Environmental Management (Elsevier) | November 9th, 2022

The decline of Pacific salmon (Oncorhynchus spp.) populations over the last few decades has stimulated major restoration efforts across the Pacific Northwest to improve t

The decline of Pacific salmon (Oncorhynchus spp.) populations over the last few decades has stimulated major restoration efforts across the Pacific Northwest to improve the status of these iconic fishes. The leading factors contributing to the decline of Pacific salmon include watershed degradation and water diversions, which result in part from widespread dam construction across the United States (Moyle, 1994). Early river restoration actions primarily focused on physical habitat alterations (e.g., in-stream habitat improvement, fish passage; Barinaga, 1996; Bernhardt et al., 2005), while more recent work has centered around restoring natural processes (Johnson et al., 2019). Since socioeconomic and political complications are typically too great for dam removal projects to be feasible, reconciliation ecology, which encourages the accommodation of both human and wildlife needs in a human-dominated landscape, can be a more effective approach to restoration (Rosenzweig, 2003; Moyle et al., 2017). Rather than the elusive goal of returning rivers to a natural flow regime, the aim can be to attain functional environmental flows to support beneficial flow-ecology relationships (Poff et al., 2017). Dams can be operated to reduce some of their detrimental effects by releasing flows that improve downstream habitat through the preservation of key hydrologic signals upon which biophysical processes and native biological communities depend (Yarnell et al., 2020). Four functional flow components were identified for Mediterranean montane streams: wet-season initiation flows, peak magnitude flows, spring recession flows, and dry-season low flows; see Yarnell et al. (2015) for a description about the importance of each key functional component. Several studies have identified the need to further assess linkages between streamflow, invertebrate prey availability, and drift-foraging dynamics for consideration in future restoration plans for juvenile salmonids (Weber et al., 2014; Naman et al., 2016; Lusardi et al., 2018). The focus of this study is to assess the impact of dam-release flows imitating one of those functional flow components, peak magnitude flows, on invertebrate drift as a food resource for juvenile salmonids.

Rethinking Management of the Colorado River through Lake Powell, Grand Canyon, and Lake Mead

Utah State University | November 15th, 2024

Reversal in estuarine sand supply driven by Holocene sea level rise: A model for sand transport in large structural estuaries, San Francisco Bay, California, USA

Elsevier | July 26th, 2024

Coastal sand supply is a critical component of shoreline stability in the face of modern threats to coastal zones such as sea level rise or anthropogenic sediment extract

Coastal sand supply is a critical component of shoreline stability in the face of modern threats to coastal zones such as sea level rise or anthropogenic sediment extraction. Understanding the natural and anthropogenically perturbed dynamics of coastal systems has become a pressing challenge for coastal communities, such as the San Francisco Bay area in the United Sates, a large structurally controlled estuary system where stakeholders seek to balance the extraction of coastal sand resources for economic use and ensure sufficient sand supply for sustaining natural coastal environments. Developing accurate and comprehensive models of sand inputs and transport pathways in different types of coastal systems is imperative to balancing these competing needs. While estuarine sediment transport has been well-studied in many systems globally, structurally controlled estuaries in tectonically active settings have received relatively less attention. The prevailing hypothesis for sediment transport through San Francisco Bay describes active input and transport of sand from a large integrated regional catchment, through multiple subembayments, and out to Pacific coast beaches; a model contrary to prevailing understanding of highstand estuarine sediment transport in most settings. We test this model by applying comprehensive sand provenance analysis to surface and near-surface sand deposits in and around San Francisco Bay coupled with sand residence time data from optically stimulated luminescence (OSL) dating. New provenance results include sand petrography modal abundances, bulk geochemistry, and U-Pb detrital zircon geochronology from 27 Holocene samples throughout the San Francisco Bay region. Collectively, these new results highlight marked sediment provenance and residence time differences between San Francisco Bay structural subembayments. In particular, distinct compositional differences and OSL ages exist between sand in the bayhead region of the estuary (OSL ages ca. 4 ka; Sacramento River/local provenance) and sand from the more distal bay regions and the Pacific coast (OSL ages ca. 1 ka; integrated Sierra Nevada provenance). These provenance differences better support a revised sand input and transport model with disconnected depocenters across three structurally restricted subembayments from bayhead to the Pacific coast. New data suggest that at present the bayhead region receives limited supply from the Sacramento-San Joaquin Delta drainage with subsidiary supply from local circum-bay drainages. Sand deposited in the region from the Pacific coast through the inlet (Golden Gate) and into the estuary consists of a combination of tidal winnowing and reworking of “relic” sand from lowstand periods combined with sand eroded from Pacific coast sea cliffs, and sand supply from local Coast Range drainages. These results suggest that sand is likely not transported directly to the Pacific coast from the Sacramento-San Joaquin Delta under modern conditions. Moreover, it is likely that structural constrictions between the main estuary and outer coast and between estuary subembayments cause abrupt cessation of sediment input from the main regional drainage during marine flooding, a feature likely common to large structurally controlled estuaries globally. This revised model for San Francisco Bay sand transport illustrates the need for research targeted at interpreting natural sand transport pathways in coastal systems where coarse sediment supply is a sustainability concern.

Review of CDFW Recommendations for the 2022 Readoption of Drought Emergency Regulations on the Scott River and Recommendations for Future Management During Extreme Drought Conditions

Siskiyou Farm Bureau | August 31st, 2022

Review of the Long-Term Operations of the Central Valley Project and the State Water Project

National Academy of Sciences (NAS) | November 10th, 2025

The CVP and SWP (referred to collectively as “the Projects”) rarely deliver their full contracted  amount of water. Some of this is inherent in the operation of larg

The CVP and SWP (referred to collectively as “the Projects”) rarely deliver their full contracted  amount of water. Some of this is inherent in the operation of large water projects with diverse demands in a dry and highly variable climate. A growing, complex regulatory environment of state and federal laws, some of which were created to protect fish species endemic to the Delta, has further restricted CVP and SWP operations.  These fish include the southern distinct population segment of North American green sturgeon, California Central Valley steelhead, Central Valley spring-run Chinook salmon, Sacramento River winter-run Chinook salmon, longfin smelt, and Delta smelt. Operating the Projects while trying to prevent species extinction can be a source of conflict if the actions to prevent extinction reduce the amount of water that can be exported. Project operation into the future will likely become more challenging as changes in various climatic factors push the listed species closer to their thresholds of survivability. Hence, in late 2023 USBR contracted with the National Academies of Sciences, Engineering, and Medicine (NASEM) to form an expert committee that could serve as an independent review for the CVP and SWP as they operate into the future. The Committee’s statement of task appears in Box S-1. The three actions chosen for the study—the Shasta Coldwater Pool Management Action, the Old and Middle River Flow Management Action, and the Summer-Fall Habitat Action for Delta Smelt— are perceived as consequential for species survival and controversial for their effects on water deliveries to contractors.