Health of Native Riparian Vegetation and its Relation to Hydrologic Conditions along the Mojave River, Southern California

U.S. Geological Survey (USGS) | July 15th, 1999

Height-related changes in forest composition explain increasing tree mortality with height during an extreme drought

Nature Portfolio (Springer Nature) | July 7th, 2020

Recently, Stovall et al. showed that during an extreme drought, remotely sensed mortality of tall trees was more than double that of short trees. They interpreted this t

Recently, Stovall et al. showed that during an extreme drought, remotely sensed mortality of tall trees was more than double that of short trees. They interpreted this to be a consequence of inherently greater hydraulic vulnerability of tall trees, and suggested that tall-tree vulnerability should generalize more broadly. Here we reassess their conclusions using contemporaneous, ground-based data from near their study sites. We find that 90% of trees belong to taxonomic groups showing declining, not increasing, mortality with height, and that the overall increase in mortality with height is instead a consequence of height-related changes in forest composition, not intrinsically greater vulnerability of tall trees. Similar mechanisms likely explain mortality patterns at Stovall et al.’s sites, and, regardless, we show that their conclusions should not be accepted in the absence of robust tests of alternative mechanisms.

Historical Ecology of the Los Angeles River Watershed and Environs, Infrastructure for a Comprehensive Analysis

University of Southern California (USC) | June 15th, 2020

Human contributions to evapotranspiration mitigate swings in dry-to-wet year transitions

Nature Portfolio (Springer Nature) | January 9th, 2026

California’s food and economic security depends on water availability, particularly under increasingly extreme climate scenarios. A key component of the water balance i

California’s food and economic security depends on water availability, particularly under increasingly extreme climate scenarios. A key component of the water balance is evapotranspiration, the combination of soil and surface evaporation and plant transpiration. Evapotranspiration is influenced by natural drivers (e.g., climate, vegetation cover) and human intervention (e.g., irrigation, land management). Here, we analyze the transition between one of California’s driest years (2022) to an exceptionally wet year (2023) to assess evapotranspiration responses to climate extremes. Despite increased precipitation, total statewide evapotranspiration changed less than 10%. In 2022, human contributions accounted for 30% of statewide evapotranspiration and 80% in managed lands. In 2023, natural evapotranspiration increased, and human contributions fell by 30%, yet still comprised nearly 50% of evapotranspiration in managed areas. Our findings underscore the enduring role of human activity on California’s hydrology, even during wet years, and demonstrate a framework to separate natural and anthropogenic controls on evapotranspiration.

Human Impacts Dominate Global Loss of Lake Ecosystem Resilience

American Geophysical Union (AGU) | June 5th, 2024

Human Use of Restored and Naturalized Delta Landscapes

University of California, Davis (UC Davis) | October 31st, 2016

Current legislation and state plans for the California Delta call for large-scale restoration of aquatic and terrestrial habitats, which will require significant changes

Current legislation and state plans for the California Delta call for large-scale restoration of aquatic and terrestrial habitats, which will require significant changes in land uses and cultural patterns to achieve. Yet landscapes that are restored for habitat for other-than human species will remain subject to human uses. This report looks at how human presence can and will continue after restoration, and considers how these uses can be best reconciled with cultural, ecological and adaptive management goals. Our one year study builds off other research projects that have explored the California Delta from an integrative human-environment perspective. It uses a landscape planning approach that attempts to push beyond single sectoral methods, seeking a holistic integration of multiple goals and land use agendas spanning across ecological, social, economic and political domains. This report’s findings are based on surveys, interviews, review of existing Delta planning literature, field work and specific landscape case studies. In general, our research supports the advancement of a reconciliation approach, which seeks synergies between ecosystem needs and the desires of those who live, work and play in the Delta, both now and in the future.

Human-wildlife conflict is amplified during periods of drought

American Association for the Advancement of Science (AAAS) | November 12th, 2025

Climate change–induced alterations to human-wildlife interactions are recognized to pose a fundamental challenge for global conservation initiatives. However, the exten

Climate change–induced alterations to human-wildlife interactions are recognized to pose a fundamental challenge for global conservation initiatives. However, the extent to which specific climatic disturbances influence dynamics of human-wildlife conflict across different taxonomic groups remains poorly understood. Here, we leverage an extensive dataset of community-derived human-wildlife conflict incidents to examine the influence of drought, represented by the variation in summed precipitation over the prior 12 months, on conflict reporting. We show that prolonged decreases in precipitation are associated with increased overall conflict occurrences across taxa and are significantly associated with increased conflict with carnivore species in particular. A future with increasingly severe and frequent droughts could lead to resource scarcity that not only causes conflict between humans but also between humans and the natural world around them.

Hydrodynamics and habitat interact to structure fish communities within terminal channels of a tidal freshwater delta

Ecological Society of America (Wiley) | January 13th, 2023

Terminal channels were historically a common feature of tidal delta ecosystems but have become increasingly rare as landscapes have been modified. Tidal hydrodynamics are

Terminal channels were historically a common feature of tidal delta ecosystems but have become increasingly rare as landscapes have been modified. Tidal hydrodynamics are a defining feature in tidal terminal channel ecosystems from which native aquatic communities have evolved. However, few studies have explored the relationship between fish community structure and hydrodynamics in these tidal terminal channel ecosystems. We sampled fish communities throughout a network of terminal channels within the northeasternmost region of the San Francisco Estuary to determine the relationship between fish community structure and hydrodynamics within these environments. We collected two years (2017 and 2018) of fish community samples using gill nets and analyzed data using multivariate community analyses and count models. We found metrics of fish diversity and counts of native fishes to be greatest upstream (farthest from tidal influence) of the tidal excursion within terminal channels. Counts of non-native fishes were less affected by this hydrodynamic feature of terminal channels and more tightly correlated to local habitat conditions (e.g., water temperature, depth). Our results suggest that channel hydrodynamics plays a role in structuring fish communities within terminal channels, particularly native fishes. These results indicate that hydrodynamics in tidal delta ecosystems may be able to be altered in ways that benefit native fishes without the cost of water pumping.

Hydrology and Hydrodynamics on the Sacramento River Near the Fremont Weir, California—Implications for Juvenile Salmon Entrainment Estimates

U.S. Geological Survey (USGS) | November 9th, 2018

Estimates of fish entrainment on the Sacramento River near the Fremont Weir are a critical component in determining the feasibility and design of a proposed notch in the

Estimates of fish entrainment on the Sacramento River near the Fremont Weir are a critical component in determining the feasibility and design of a proposed notch in the weir to increase access to the Yolo Bypass, a seasonal floodplain of the Sacramento River. Detailed hydrodynamic and velocity measurements were made at a river bend near the Fremont Weir in the winter and spring of 2016 to examine backwater conditions and estimate the hydraulic entrainment zone, a zone where fish would be predicted to be entrained into the notch. Secondary circulation near the river bend was shown to shift the velocity and discharge distributions toward the outside of the bend. Variability in the stage-discharge relation was shown to be the biggest source of uncertainty in determining the location of the hydraulic entrainment zone. Outflow from the Sutter Bypass and high flow on the Feather River resulted in backwater conditions near the Fremont Weir about 25 percent of the time over the 27-year period from April 1990–April 2017. Velocity measurements used to estimate the critical streakline position (the outer edge of the hydraulic entrainment zone) were not made over a sufficient range of conditions to explicitly quantify the variability in the location of the critical streakline. The variability in the critical streakline position was therefore represented stochastically with a random effects model. The estimated position of the critical streakline and the random effects model are input parameters used in a simulation designed to estimate fish entrainment over a 15-year period. The estimates of the critical streakline and likely fish entrainment could be much improved with velocity measurements over a broader range of stage and discharge conditions. 

Hydrology, Ecology, and Fishes of the Klamath River Basin (2008)

National Academy of Sciences (NAS) | January 1st, 2008

The Klamath River basin, which spans parts of southern Oregon and northern California, has been the focus of a prominent conflict over competing uses for water. Manag

The Klamath River basin, which spans parts of southern Oregon and northern California, has been the focus of a prominent conflict over competing uses for water. Management actions to protect threatened and endangered fish species in the basin have left less water available for irrigation in dry years and heightened tensions among farmers and other stakeholders including commercial fishermen, Native Americans, conservationists, hunters, anglers, and hydropower producers. This National Research Council report assesses two recent studies that evaluate various aspects of flows in the Klamath basin: (1) the Instream Flow Phase II study (IFS), conducted by Utah State University, and (2) the Natural Flow of the Upper Klamath Basin study (NFS), conducted by the U.S. Bureau of Reclamation (USBR). The report concludes that both studies offer important new information but do not provide enough information for detailed management of flows in the Klamath River, and it offers many suggestions for improving the studies. The report recommends that a comprehensive analysis of the many individual studies of the Klamath river basin be conducted so that a big picture perspective of the entire basin and research and management needs can emerge. Key Messages If these conclusions were borne out by studies incorporating experimental flows and monitored responses, managers would be able to have greater confidence that decisions to increase flows would have a beneficial effect on anadromous fishes in the lower river The Instream Flow Study Phase II did not include important water-quality attributes, such as dissolved oxygen levels, nutrient loadings, contaminants, and sediment concentrations, although each has important implications for the vitality of the fish populations of the Klamath River. The Natural Flow Study and the Instream Flow Study Phase II were major science and engineering investigations, but the linkage of one to the other was only partially achieved. The Natural Flow Study was seriously compromised by several fundamental issues, including its choice of a basic approach for understanding natural flows, choices of the models for calculations, and serious omissions of factors likely to influence river flows at the Iron Gate Dam gauge site. The basin and its biota have changed so much in the past century that the implications for the fishes of restoring natural flows are not clear. The committee concluded that the Natural Flow Study includes calculated flows that are at best first approximations to useful estimates of such flows. The committee found important shortcomings in the Instream Flow Study Phase II and its use of various models and data. Two major shortcomings use of monthly data and lack of tributary analyses are so severe that that they should be addressed before decision makers can use the outputs of the study to establish precise flow regimes with confidence. The most important outcome of the Instream Flow Study was that it indicated that increases in existing flows downstream from Iron Gate Dam probably would benefit fish populations through improved physical habitat associated with more water and through reduced water temperatures. There was a lack of a thorough assessment of the relationship between flow-data time series and the behavior of different species and life stages and the population dynamics of coho and Chinook salmon When the science needs for the basin are better characterized, the individual studies necessary to create a sound science-based body of knowledge for decision makers and managers will be more easily identified. current flow regime. These are improvements in flow because they include intra- and inter-annual variations and probably will enhance Chinook salmon growth and young-of-the-year production. is not possible to know how well the recommendations apply to any one species or to all the species as a whole. Indeed, most of the information was from Chinook salmon, which suggests that confidence in its applicability to that species would be greater than to other species. of the representativeness of the reaches used for detailed study, and the statistical approach to analyze the calculated set of instream flows did not use normalized data and did not have provisions for identifying serial autocorrelations.