From climate-change spaghetti to climate-change distributions for 21st Century California

M. D. Dettinger

Home/Archive/USGS

USGS · 70175022

From climate-change spaghetti to climate-change distributions for 21st Century California

M. D. Dettinger

View original source ↗Export metadata ↓

Abstract

The uncertainties associated with climate-change projections for California are unlikely to disappear any time soon, and yet important long-term decisions will be needed to accommodate those potential changes. Projection uncertainties have typically been addressed by analysis of a few scenarios, chosen based on availability or to capture the extreme cases among available projections. However, by focusing on more common projections rather than the most extreme projections (using a new resampling method), new insights into current projections emerge: (1) uncertainties associated with future greenhouse-gas emissions are comparable with the differences among climate models, so that neither source of uncertainties should be neglected or underrepresented; (2) twenty-first century temperature projections spread more, overall, than do precipitation scenarios; (3) projections of extremely wet futures for California are true outliers among current projections; and (4) current projections that are warmest tend, overall, to yield a moderately drier California, while the cooler projections yield a somewhat wetter future. The resampling approach applied in this paper also provides a natural opportunity to objectively incorporate measures of model skill and the likelihoods of various emission scenarios into future assessments.

Explore related subjects

San Francisco Estuary and Watershed Science Article

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

M. D. Dettinger. 2005. From climate-change spaghetti to climate-change distributions for 21st Century California. https://pubs.usgs.gov/publication/70175022

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2026

Assessment of Chinook Salmon smolt survival at offsite release locations in the Sacramento River across wet and dry years

We used acoustic telemetry to estimate survival of tagged release groups, and quantify differences between alternative hatchery release strategies. To assess whether offsite release could increase survival of hatchery fish relative to those released at the hatchery, we compare survival during emigration of hatchery fall Chinook Salmon (FCS, Oncorhynchus tshawytscha ) smolts released onsite, at Coleman National Fish Hatchery (NFH), to those released at alternative offsite locations downstream in the upper Sacramento River, California. Approximately 300 fish in each release group were implanted with acoustic tags in the 3-year study during 2019, 2021, and 2022. Environmental conditions in the emigration corridor varied between study years, with extended high flows in 2019, whereas drought conditions and a flat hydrograph occurred in 2021 and 2022. Survival across years appeared to reflect environmental conditions, with higher overall survival seen in 2019. Survival differences between release sites generally showed higher cumulative survival to Knights Landing or Chipps Island for the downstream release groups, compared to the onsite releases during 2021 and 2022. This information suggests hatchery releases of FCS from Coleman NFH at downstream release sites may benefit emigration survival during years of drought and sub-optimal in-river conditions, compared to standard onsite releases. Hatchery managers can use information from this study to diversify the portfolio of release strategies, which may be useful to buffer against extreme variations of adult abundance by spreading risks across space and time. Ultimately, offsite releases may be a useful tool for adaptive management of these culturally, ecologically, and economically important salmon populations.

California↗

USGS2026

Differences among runs of Chinook Salmon in routing probability at the Georgiana Slough-Sacramento River junction

The survival of juvenile Chinook Salmon ( Oncorhynchus tshawytscha ) depends on the specific migration route they take through the Sacramento–San Joaquin Delta. Factors such as flow magnitude, flow direction, and distribution of fish across the channel significantly affect the likelihood of their entering routes with lower survival probabilities. Management strategies to mitigate the entry of endangered winter-run and threatened spring-run Chinook Salmon into the interior Delta—particularly through Georgiana Slough—involve flow regulation and the installation of a bioacoustic fish fence. Monitoring the effectiveness of these measures has primarily relied on acoustically-tagged, juvenile, hatchery-reared, late-fall-run Chinook Salmon, which are easier to obtain and can accommodate larger tags compared to other runs. Previous studies explored how flow dynamics affect routing probabilities of late-fall-run Chinook Salmon, but there is a lack of understanding about how routing probabilities vary among runs. We leveraged data from 15 previous studies comprising 3,004 acoustically-tagged fish across all four runs, over a 12-year period, to assess the effects of run on routing probability into Georgiana Slough, while accounting for variation in flow dynamics. We employed logistic regression to model the influence of tidal flow metrics, time of day (day and night), and run type on the probability of juvenile Chinook Salmon being routed into Georgiana Slough. Our analysis revealed that reverse flow during incoming tides influenced the routing probabilities of all runs. An increased proportion of flow into Georgiana Slough, meant an increased probability for all runs to be routed into Georgiana Slough. Late-fall-run Chinook Salmon also showed a greater probability of routing into Georgiana Slough during the night than during the day, whereas the opposite was true for other runs. These differences in routing probability affect our understanding of how management actions intended to reduce routing into Georgiana Slough may differentially affect the four runs of Chinook Salmon in the Sacramento River.

Callifornia↗

USGS2025

Effects of flow on pesticides in water and zooplankton in the northern Sacramento-San Joaquin Delta

Zooplankton are a key food source for juvenile fishes in estuaries worldwide, including California’s Sacramento–San Joaquin Delta (hereafter Delta); both zooplankton quality and quantity are critical to ecosystem health. Zooplankton may be affected by pesticides in water and the food web, and the Delta is known to contain complex pesticide mixtures. In this study, we evaluated pesticide concentrations in water and zooplankton in the northern Delta during (1) the summer–fall of 2017, 2018, and 2019, which included periods of augmented pulse flows from agriculture tailwater, and (2) across a full seasonal cycle from May 2019 to March 2020. We quantified changes in pesticide concentration in response to environmental factors. We found that zooplankton showed more frequent detections of hydrophobic pesticides compared to more frequent detections of hydrophilic compounds in water. Pesticide concentrations were influenced by flow, pesticide application, and season, but the effects of these environmental factors differed by habitat (Sacramento River or Yolo Bypass Toe Drain). Pesticides in water responded similarly to environmental factors in the Sacramento River and Yolo Bypass, whereas pesticides in zooplankton responded differently. In water, we found more detections and higher concentrations at higher flows in the Yolo Bypass and Sacramento River, but responses to pesticide application varied by habitat. Alternatively, pesticide concentrations in zooplankton increased in the Yolo Bypass with increasing flow (correlated with flow pulses) and changed seasonally; whereas, pesticide concentrations in zooplankton in the Sacramento River decreased at higher flows, and decreased with or did not respond to higher pesticide application in the watershed. Our study suggests that augmented flows—particularly those using agricultural tailwater—may have unintended negative ecological effects that could partially offset benefits to the food web and fishes in the northern Delta, underscoring the complex interplay among factors that drive increased pesticide exposure.

California↗