Declining groundwater storage expected to amplify mountain streamflow reductions in a warmer world

Nature Portfolio (Springer Nature) | May 23rd, 2024

Groundwater interactions with mountain streams are often simplified in model projections, potentially leading to inaccurate estimates of streamflow response to climate ch

Groundwater interactions with mountain streams are often simplified in model projections, potentially leading to inaccurate estimates of streamflow response to climate change. Here, using a high-resolution, integrated hydrological model extending 400 m into the subsurface, we find groundwater an important and stable source of historical streamflow in a mountainous watershed of the Colorado River. In a warmer climate, increased forest water use is predicted to reduce groundwater recharge resulting in groundwater storage loss. Losses are expected to be most severe during dry years and cannot recover to historical levels even during simulated wet periods. Groundwater depletion substantially reduces annual streamflow with intermittent conditions predicted when precipitation is low. Expanding results across the region suggests groundwater declines will be highest in the Colorado Headwater and Gunnison basins. Our research highlights the tight coupling of vegetation and groundwater dynamics and that excluding explicit groundwater response to warming may underestimate future reductions in mountain streamflow.

Declining mountain snowpack in western North America

American Meteorological Society (AMS) | January 3rd, 2005

Mountain snowpack in western North America is a key component of the hydrologic cycle, storing water from the winter (when most precipitation falls) and releasi

Mountain snowpack in western North America is a key component of the hydrologic cycle, storing water from the winter (when most precipitation falls) and releasing it in spring and early summer, when economic, environmental, and recreational demands for water throughout the West are frequently greatest. In most river basins of the West, especially in Washington, Oregon, and California, snow (rather than man-made reservoirs) is the largest component of water storage; hence, the West is (to varying degrees) vulnerable to climatic variations and changes that influence spring snowpack.

Delta Conveyance Project: Modernizing California’s Water Infrastructure, Fast Facts 2024

California Department of Water Resources (DWR) | September 13th, 2023

DRAFT Staff Report/Substitute Environmental Document in Support of Potential Updates to the Water Quality Control Plan for the San Francisco Bay/Sacramento-San Joaquin Delta Estuary for the Sacramento River and its Tributaries, Delta Eastside Tributaries, and Delta

California State Water Resources Control Board (SWRCB) | September 28th, 2023

Droughts impede water balance recovery from fires in the Western United States

Nature Portfolio (Springer Nature) | January 2nd, 2024

A steady rise in fires in the Western United States, coincident with intensifying droughts, imparts substantial modifications to the underlying vegetation, hydrology and

A steady rise in fires in the Western United States, coincident with intensifying droughts, imparts substantial modifications to the underlying vegetation, hydrology and overall ecosystem. Drought can compound the ecosystem disturbance caused by fire, although how these compound effects on hydrologic and ecosystem recovery vary among ecosystems is poorly understood. Here we use remote sensing-derived high-resolution evapotranspiration (ET) estimates from before and after 1,514 fires to show that ecoregions dominated by grasslands and shrublands are more susceptible to drought, which amplifies fire-induced ET decline and, subsequently, shifts water flux partitioning. In contrast, severely burned forests recover from fire slowly or incompletely, but are less sensitive to dry extremes. We conclude that moisture limitation caused by droughts influences the dynamics of water balance recovery in post-fire years. This finding explains why moderate to extreme droughts aggravate impacts on the water balance in non-forested vegetation, while moisture accessed by deeper roots in forests helps meet evaporative demands unless severe burns disrupt internal tree structure and deplete fuel load availability. Our results highlight the dominant control of drought on altering the resilience of vegetation to fires, with critical implications for terrestrial ecosystem stability in the face of anthropogenic climate change in the West.

Drowned Memories: The Submerged Places of the Winnemem Wintu

Journal of the World Archaeological Congress (Springer) | July 7th, 2009

This article is a brief overview of an instance where landscape inundation has disconnected culture from place. The Winnemem Wintu, a Native American tribe in Northern Ca

This article is a brief overview of an instance where landscape inundation has disconnected culture from place. The Winnemem Wintu, a Native American tribe in Northern California, had most of their ancestral landscape along the McCloud River submerged by the construction of Shasta Dam just after World War II. The tribe’s remaining traditional cultural properties are under continual threat of loss and/or destruction, leaving the tribe’s ability to practice traditional ceremonies crippled by legal battles and fights against the continual assertion of United States hegemonic power over tribal cultural identity. As part of archaeological research on these submerged places, the tribe’s spiritual leader, Caleen Sisk-Franco, and Tribal Headman, Mark Franco, spoke with the author about these threats and how their culture must adapt to meet them.

Effects of salinity on olfactory toxicity and behavioral responses of juvenile salmonids from copper

Aquatic Toxicology (Elsevier) | April 4th, 2016

Dissolved copper is one of the more pervasive and toxic constituents of stormwater runoff and is commonly found in stream, estuary, and coastal marine habitats of juvenil

Dissolved copper is one of the more pervasive and toxic constituents of stormwater runoff and is commonly found in stream, estuary, and coastal marine habitats of juvenile salmon. While stormwater runoff does not usually carry copper concentrations high enough to result in acute lethality, they are of concern because sublethal concentrations of copper exposure have been shown to both impair olfactory function and alter behavior in various species in freshwater. To compare these results to other environments that salmon are likely to encounter, experiments were conducted to evaluate the effects of salinity on the impairment of olfactory function and avoidance of copper. Copper concentrations well within the range of those found in urban watersheds, have been shown to diminish or eliminate the olfactory response to the amino acid, l-serine in freshwater using electro-olfactogram (EOG) techniques. The olfactory responses of both freshwater-phase and seawater-phase coho and seawater-phase Chinook salmon, were tested in freshwater or seawater, depending on phase, and freshwater-phase coho at an intermediate salinity of 10‰. Both 10‰ salinity and full strength seawater protected against the effects of 50 μg copper/L. In addition to impairing olfactory response, copper has also been shown to alter salmon behavior by causing an avoidance response. To determine whether copper will cause avoidance behavior at different salinities, experiments were conducted using a multi-chambered experimental tank. The circular tank was divided into six segments by water currents so that copper could be contained within one segment yet fish could move freely between them. The presence of individual fish in each of the segments was counted before and after introduction of dissolved copper (<20 μg/L) to one of the segments in both freshwater and seawater. To address whether use of preferred habitat is altered by the presence of copper, experiments were also conducted with a submerged structural element. The presence of sub-lethal levels of dissolved copper altered the behavior of juvenile Chinook salmon by inducing an avoidance response in both freshwater and seawater. While increased salinity is protective against loss of olfactory function from dissolved copper, avoidance could potentially affect behaviors beneficial to growth, survival and reproductive success.

Environmental Health Risks from Abandoned Mines in the Sierra Nevada

Sierra Fund | June 9th, 2014

The widespread pollution from Gold Rush mining activities, including mercury, arsenic and lead, constitutes the oldest and longest neglected environmental justice problem

The widespread pollution from Gold Rush mining activities, including mercury, arsenic and lead, constitutes the oldest and longest neglected environmental justice problem in California. The effects of this pollution on human health and the environment are only now beginning to be addressed. Today, the effects of historic mining pollution are an invisible but very real threat to people who live, work or recreate in the Sierra Nevada. Toxins of concern include mercury, arsenic, lead and asbestos.  There is little information about these potential exposures available to Sierra residents. State-issued fish consumption advisories in the region do not provide site-specific advice for many locations people fish, or the species people eat. In 2006, The Sierra Fund, in partnership with California State University Chico, conducted a survey of Sierra clinics. This study found that not one of 13 surveyed clinics included information on mercury in fish as part of their maternal/infant health programs, whether caught locally or not. Additionally, the study learned that none of the clinics surveyed administer an environmental health history form, so it is difficult to connect current health problems to environmental exposures. In order to address this lack of information and provide a springboard for more research, The Sierra Fund conducted three pilot studies of potential environmental exposures in 2009 and 2010 and a pilot outreach program to present these findings to Sierra communities in 2013-14. This report summarizes findings and recommendations from these efforts, in order to encourage continued research into these potentially serious health exposures.

Estimates of Natural and Unimpaired Flows for the Central Valley of California: Water Years 1922-2014 (draft)

California Department of Water Resources (DWR) | March 1st, 2016

Estimating regional water supplies that would have occurred absent human activities is a common practice in water resources planning. In this report, such theor

Estimating regional water supplies that would have occurred absent human activities is a common practice in water resources planning. In this report, such theoretical water supply estimates are referred to as “unimpaired” flow. Since 1980, the Department of Water Resources (Department) has periodically published estimates of Central Valley unimpaired flows. In spite of the Department’s previous attempts to distinguish between natural conditions and its calcula tion of theoretical unimpaired flows, unimpaired flow estimates have frequently been used as a surrogate measure of natural conditions, presumably because natural flow estimates were unavailable. A major objective of this report is to clarify the conceptua l differences between natural and unimpaired flows. In this report, the term “unimpaired” flow is used to describe a theoretically available water supply assuming existing river channel conditions in the absence of (1) storage regulation for water supply a nd hydropower purposes and (2) stream diversions for agricultural and municipal uses. Unimpaired flow estimates are theoretical in that such conditions have not occurred historically. In pristine watersheds which have undergone little land use change, unim paired flow estimates provide a fixed frame of reference to develop relationships between precipitation, runoff, and water supply based on long - term hydrologic records. For many years these relationships were based on the assumption of stationarity, i.e. that the past is a good indicator of the future. However, global warming now requires hydrologists and water resources managers to analyze non-stationary processes, requiring more sophisticated tools and techniques to quantify future water supplies. This report updates and extends the Department’s previous published estimates of unimpaired flows for 24 Central Valley sub-basins and the Delta. Monthly unimpaired flows are presented for water years 1922 - 2014.

Estimating evapotranspiration change due to forest treatment and fire at the basin scale in the Sierra Nevada, California: Forest Disturbance and Evapotranspiration Change

Ecohydrology (Wiley) | April 6th, 2018

We investigated the potential magnitude and duration of forest evapotranspiration (ET) decreases resulting from forest‐thinning treatments and wildfire in west‐slope

We investigated the potential magnitude and duration of forest evapotranspiration (ET) decreases resulting from forest‐thinning treatments and wildfire in west‐slope watersheds of the Sierra Nevada range in California, USA, using a robust empirical relation between Landsat‐derived mean‐annual normalized difference vegetation index (NDVI) and ET measured at flux towers. Among forest treatments, the minimum observed NDVI change required to produce a significant departure from control plots with NDVI of about 0.70 was −0.09 units, corresponding to a basal‐area reduction of 29.1 m2/ha (45% reduction) and equivalent to an estimated ET reduction of 153 mm/year (21% change; approximate mean annual precipitation = 1,000 mm). Intensive thinning in highly productive forests that approached prefire‐exclusion densities reduced basal area by 40–50%, generating estimated ET reductions of 153–218 mm/year (21–27% change) over 5 years following treatment. Low‐intensity underburn treatments resulted in no significant change in ET. Examining the cumulative impact of wildfires on ET between 1990 and 2008, we found that the lower and wetter American River basin (5,310 km2) generated more than twice the ET reduction per unit area than those in the higher and drier Kings River basin (4,790 km2), corresponding to greater water and energy limitations in the latter and greater fire severity in the former. A rough extrapolation of these results to the entire American River watershed suggests that ET reductions due to forest thinning by wildfire could approach 10% of full natural flows for dry years and 5% over all years.