California Climate Research Articles

Long-Term Hydrologic Variability in the Instrumental Record of California Climate

This study characterizes the instrumental record of California climate for the last 170 years. Our goal is to look for hydrologic variability at decadal and longer time scales that would be consistent with paleoclimate estimates of hydrologic variability in California for the last 3000 years. Our study focuses on meteorological summaries of annual precipitation and temperature. The precipitation records go back as far as 1850; the temperature records go back as far as 1880. California hydrologic records show strong variability at the interannual level due to ENSO forcing. They also all show a strong decadal (~14 yr) cyclicity and evidence for multi-decadal to centennial variability that is consistent with California paleoclimate studies. California temperature records show a long-term warming of 5 °F−6 °F (2.8 °C−3.4 °C) associated with global warming, but there is no evidence for a similar long-term trend in hydrologic variability. Long-term Pacific Ocean variability adjacent to central and northern California, Pacific Decadal Oscillation (PDO) and North Pacific Gyre Oscillation (NPGO), show a similar decadal to centennial pattern of variability that we associate with our long-term hydrologic variability. The positive phase of the NPGO and the negative phase of the PDO are associated with the decadal scale (~14 yr) dry cycles in California for the last 70 years.

California Current temperatures adjacent to Southern California: 1949–2020

The southward flowing California Current, which lies adjacent to the California Pacific coastline as part of the North Pacific Ocean gyre circulation, is an important element in characterizing California's climate variability. This study improves and extends the historic record of California Current temperatures along the Southern California coastline for the last 71 years. The data come from long-term sea surface temperature measurements determined by the California Cooperative Oceanic Fisheries Investigations (CalCOFI) partners. The sea-surface temperature measurements come from a grid of 31 oceanic sampling sites within the core of the California Current off the Southern California coast. The sites have been sampled intermittently over the course of each year with ∼100 measurements/year on average. The Southern California Current temperatures in our grid have risen ∼2.5 °C since 1949.The California current temperatures are strongly correlated with the larger-scale North Pacific Ocean Pacific Decadal Oscillation (PDO) index and the North Pacific Gyre Oscillation (NGPO) index. All three show distinctive correlation with decadal (∼14-yr) California rainfall cyclicity.

Climatically robust multiscale species distribution models to support pronghorn recovery in California.

We combined two climate-based distribution models with three finer-scale suitability models to identify habitat for pronghorn recovery in California now and into the future. We used a consensus approach to identify areas of suitable climate now and future for pronghorn in California. We compared the results of climate models from two separate hypotheses about their historical ecology in the state. Under the migration hypothesis, pronghorn were expected to be limited climatically by extreme cold in winter and extreme heat in summer; under the niche reduction hypothesis, historical pronghorn of distribution would have better represented the climatic limitations of the species. We combined occurrences from GPS collars distributed across three populations of pronghorn in the state to create three distinct habitat suitability models: (1) an ensemble model using random forests, Maxent, classification and regression Trees, and a generalized linear model; (2) a step selection function; and (3) an expert-driven model. We evaluated consensus among both the climate models and the suitability models to prioritize areas for, and evaluate the prospects of, pronghorn recovery. Climate suitability for pronghorn in the future depends heavily on model assumptions. Under the migration hypothesis, our model predicted that there will be no suitable climate in California in the future. Under the niche reduction hypothesis, by contrast, suitable climate will expand. Habitat suitability also depended on the methods used, but areas of consensus among all three models exist in large patches throughout the state. Identifying habitat for a species which has undergone extreme range collapse, and which has very fine scale habitat needs, presents novel challenges for spatial ecologists. Our multimethod, multihypothesis approach can allow habitat modelers to identify areas of consensus and, perhaps more importantly, fill critical knowledge gaps that could resolve disagreements among the models. For pronghorn, a better understanding of their upper thermal tolerances and whether historical populations migrated will be crucial to their potential recovery in California and throughout the arid Southwest.

Placing 21st Century Warming in Southern California, USA in a Multi-Century Historical Context

Warming in southern California during the 21st century is unprecedented in the instrumental record. To place this warming in a multi-century historical context, we analyzed tree ring data sampled from Jeffrey pine (Pinus jeffreyi) and sugar pine (Pinus lambertiana) collected from minimally disturbed, old-growth high-elevation forests within Mt. San Jacinto State Park California, USA. Based on a calibration/verification period of 1960–2020 between earlywood radial growth and California Climate Division 6 climate data, we reconstructed annual (November–October) minimum temperature (Tmin) from 1658 to 2020. During the 61-year calibration/verification period, instrumental Tmin increased (r = 0.69, p < 0.01) and was positively associated with annual radial growth (r = 0.71, p < 0.01). Using regime shift analysis, we found that the 363-year reconstruction revealed Tmin stability until 1958 and then decreased until 1980, followed by the two warmest regimes (1981–2007, 2008–2020) on record. The last 13-year period was 0.77 °C warmer than the multi-century average with nine of the ten warmest years in the reconstruction recorded. These results suggest that 21st century warming in southern California is unique in the context of the past four centuries, indicating the rarity of exceptional warmth captured in the tree ring record.

Leveraging regional mesh refinement to simulate future climate projections for California using the Simplified Convection-Permitting E3SM Atmosphere Model Version 0

Abstract. The spatial heterogeneity related to complex topography in California demands high-resolution (< 5 km) modeling, but global convection-permitting climate models are computationally too expensive to run multi-decadal simulations. We developed a 3.25 km California climate modeling framework by leveraging regional mesh refinement (CARRM) using the U.S. Department of Energy (DOE)'s global Simple Cloud-Resolving E3SM Atmosphere Model (SCREAM) version 0. Four 5-year time periods (2015–2020, 2029–2034, 2044–2049, and 2094–2099) were simulated by nudging CARRM outside California to 1° coupled simulation of E3SMv1 under the Shared Socioeconomic Pathways (SSP)5-8.5 future scenario. The 3.25 km grid spacing adds considerable value to the prediction of the California climate changes, including more realistic high temperatures in the Central Valley and much improved spatial distributions of precipitation and snowpack in the Sierra Nevada and coastal stratocumulus. Under the SSP5-8.5 scenario, CARRM simulation predicts widespread warming of 6–10 °C over most of California, a 38 % increase in statewide average 30 d winter–spring precipitation, a near-complete loss of the alpine snowpack, and a sharp reduction in shortwave cloud radiative forcing associated with marine stratocumulus by the end of the 21st century. We note a climatological wet precipitation bias for the CARRM and discuss possible reasons. We conclude that SCREAM RRM is a technically feasible and scientifically valid tool for climate simulations in regions of interest, providing an excellent bridge to global convection-permitting simulations.

Sphingomonas clade and functional distribution with simulated climate change.

Microbes are essential for the functioning of all ecosystems, and as global warming and anthropogenic pollution threaten ecosystems, it is critical to understand how microbes respond to these changes. We investigated the climate response of Sphingomonas, a widespread gram-negative bacterial genus, during an 18-month microbial community reciprocal transplant experiment across a Southern California climate gradient. We hypothesized that after 18 months, the transplanted Sphingomonas clade and functional composition would correspond with site conditions and reflect the Sphingomonas composition of native communities. We extracted Sphingomonas sequences from metagenomic data across the gradient and assessed their clade and functional composition. Representatives of at least 12 major Sphingomonas clades were found at varying relative abundances along the climate gradient, and transplanted Sphingomonas clade composition shifted after 18 months. Site had a significant effect (PERMANOVA; P < 0.001) on the distribution of both Sphingomonas functional (R2 = 0.465) and clade composition (R2 = 0.400), suggesting that Sphingomonas composition depends on climate parameters. Additionally, for both Sphingomonas clade and functional composition, ordinations revealed that the transplanted communities shifted closer to the native Sphingomonas composition of the grassland site compared with the site they were transplanted into. Overall, our results indicate that climate and substrate collectively determine Sphingomonas clade and functional composition.IMPORTANCESphingomonas is the most abundant gram-negative bacterial genus in litter-degrading microbial communities of desert, grassland, shrubland, and forest ecosystems in Southern California. We aimed to determine whether Sphingomonas responds to climate change in the same way as gram-positive bacteria and whole bacterial communities in these ecosystems. Within Sphingomonas, both clade composition and functional genes shifted in response to climate and litter chemistry, supporting the idea that bacteria respond similarly to climate at different scales of genetic variation. This understanding of how microbes respond to perturbation across scales may aid in future predictions of microbial responses to climate change.

Assessing the Impact of Water Conservation on Cooling Potential of Two Turfgrass Species

Highlights Empirical CWSI was developed for 'Westcoaster' tall fescue and ‘Tifgreen’ hybrid bermudagrass. The canopy temperature of both species was monitored under multiple irrigation scenarios. Deficit irrigation might reduce the cooling benefits of irrigated urban lawns. Abstract. Canopy temperature provides valuable information for efficient irrigation management and for detecting drought injury in a fast and non-destructive way. It also helps quantify the trade-offs between water conservation and the cooling benefit of the irrigated urban landscape, a critical issue in semiarid inland southern California with limited available water resources. Two adjacent hybrid bermudagrass and tall fescue irrigation trials were conducted to determine canopy temperature changes under a wide range of irrigation treatments from 2017 to 2019 in Riverside, California, USA. The canopy temperature data were also used to develop an empirical crop water stress index (CWSI) for each species. The CWSI values ranged from -0.15 to 0.71 for tall fescue and from -0.28 to 0.54 for hybrid bermudagrass. We observed a moderate correlation between visual rating scores (VR) and CWSI values for tall fescue (r = -0.68) and hybrid bermudagrass (r = -0.61). The fitted linear regression between VR and CWSI data suggested CWSI thresholds close to zero for both species to maintain their acceptable visual quality. The irrigation level consistently showed a significant effect on canopy temperature for both species. On average, a 10% decrease in irrigation application increased the canopy temperature of tall fescue and hybrid bermudagrass by 1.3°C and 0.9°C, respectively. Therefore, deficit irrigation might reduce the cooling benefits of irrigated urban lawns in the semiarid climate of inland southern California. Keywords: Canopy temperature, Evapotranspiration, Smart irrigation controller, Urban heat island, Urban irrigation, Water conservation.

Working sunset to sunrise: union strategies in three California climate transitions

ABSTRACT We evaluate the conditions and consequences of union strategies in three industrial transitions in California, all driven by its globally influential climate policies: in construction (solar power plants), electricity (nuclear power retirement), and manufacturing (electric vehicles). Building on recent, global frameworks in environmental labor studies, we grow the field’s attention towards unions with workers transitioning between ‘sunset’ industries like fossil energy and ‘sunrise’ sectors like clean energy. Using original ethnographic and archival data, we analyze the conditions that shaped union strategies in transitions, and how these in turn impacted union power and coalitions. We argue that union strategies embraced climate transitions when they organized leverage to define a shift on their members’ terms, independently from employers, often by turning environmental regulation to the advantage of labor and its allies.

Detailed evaluation of electric demand load shifting potential of heat pump water heaters in a hot humid climate

Heat pump water heaters (HPWH) are a proven method of reducing water heating energy use over prevailing electric resistance systems (ERWH). Both technologies lend themselves to enhanced control for peak load reduction. Laboratory tests were conducted in Central Florida using the CTA-2045 standard to evaluate load shifting strategies with connected water heaters. Four HPWHs from three manufacturers, including two different tank volumes, were tested alongside an ERWH in a garage-like environment. Tests aimed to shift energy use away from utility peak load periods to off-peak times when excess renewable energy resources are often available. Two load-shifting strategies were shown effective, Shed and Critical Peak, with variation by manufacturer. Beyond draw volume, other factors influenced HPWH load shifting: Florida winter conditions, which increase the energy used per draw, provided the greatest challenges to complete load shift. Inlet water temperature had a large impact on the success of load reduction. Ground temperatures in which water pipes were buried largely determined inlet water temperatures. HPWH efficiency setting: Heat pump water heaters often default to a “hybrid” mode that may use some electric resistance heat to minimize risk of running out of hot water. Operational mode can impact load shifting potential.

Western pine beetle voltinism in a changing California climate

Abstract Recent hot droughts in California resulted in ponderosa pine (Pinus ponderosa) mortality attributed to drought and western pine beetle (WPB, Dendroctonus brevicomis). While drought alone can cause tree death, direct warming effects on WPB are a contributing factor. Research on WPB generation timing (voltinism), however, is lacking. We monitored WPB tree attacks and adult emergence timing at two California sites and developed a degree‐day model from field‐observed data. Historical, contemporary, and future temperatures for several California sites were used with the model to examine trends in WPB voltinism. Field data showed a single summer and an overwinter generation at a northern California site. As summer temperatures increased beyond 1900–1980 averages, the predicted number of full and partial WPB generations by 2021 had increased from ~2 annual (one summer and one overwinter) generations historically to ~2.3 at two northern California sites and from ~2.3 to ~3.2 at two warmer California sites. Historical and contemporary data suggest winter warming was not sufficient for an additional generation overwinter. Instead, increases in generations were driven by summer and fall temperatures. Unconstrained increases in the number of future annual generations will be limited by complex, but not well understood, WPB thermal adaptations. Increased knowledge of temperature‐driven WPB population growth will improve forest vegetation models aimed at predicting ponderosa pine mortality in a changing climate.

Bioclimatic Characterisation of Specific Native Californian Pinales and Their Future Suitability under Climate Change.

Rising temperatures and changes in precipitation patterns under climate change scenarios are accelerating the depletion of soil moisture and increasing the risk of drought, disrupting the conditions that many plant species need to survive. This study aims to establish the bioclimatic characterisation, both qualitative and quantitative, of ten native Californian Pinales for the period 1980-2019, and to determine their habitat suitability by 2050. To achieve this, an exhaustive search of the Gbif database for records of ten conifer taxa was carried out. To conduct the bioclimatic characterisation of the studied taxa, we worked with the monthly values of average temperature and precipitation for the period 1980-2019 from 177 meteorological stations. Linear regressions was performed in order to compile the future evolution of California's climate. Suitable areas and optimal areas were defined at the present time (1980-2019) and its future projection (2050). We applied Boolean logic and, in this investigation, the Conditional Logic Operator (CON) was used to determine the possible species presence (one) or absence (zero) for each of the 15 variables analysed. In general, most of the conifers studied here will experience a reduction in their habitat range in California by the year 2050 due to climate change, as well as the displacement of species towards optimal areas. Furthermore, the results have highlighted the applicability of bioclimatology to future conditions under climate change. This will aid conservation managers in implementing strategic measures to ameliorate the detrimental impacts of climate change, thereby ensuring the ecological integrity and sustainability of the affected conifer species.

Cover Crops and No-Tillage Show Negligible Effects on Grapevine Physiology in Mediterranean Vineyard Agroecosystems

This study aimed to evaluate the effects of annual or perennial cover crops and tillage regimes on whole grapevine physiology and berry composition. We studied the interactive effects of tillage and cover crops on grapevine water status, leaf gas exchange, components of yield, berry composition and resulting water footprint in two contrasting production regions (Fresno County-hot climate and Napa County-warm climate) of California. The treatments included a perennial grass (PG), resident vegetation (RV), and an annual grass (AG) grown under conventional tillage (CT) and no-till (NT) settings. Neither cover crop nor tillage affected grapevine leaf gas exchange. However, at the Napa County vineyard, NT detrimentally affected grapevine water status compared to CT. Grapevine mineral nutrition, when assessed during anthesis revealed no effects of cover cropping in either year or at either location. Cover crop type did not affect yield components or berry composition, however CT increased titratable acidity (TA) at both sites. The water footprint of vineyards at either location was not affected by cover crops or tillage. Our results provided evidence that both in hot and warm climate vineyards cover cropping had negligible beneficial effects on grapevine physiology, mineral nutrition or productivity with no detrimental effects on vineyard water footprint; tillage was beneficial in younger vineyards to improve plant water status in semi-arid regions.

Trade-offs in adapting to changes in climate, land use, and water availability in California

Trade-offs in adapting to changes in climate, land use, and water availability in California

Analyzing California Climate Change Time Series Data and Its Impact on Crop Production

Climate change has become an increasingly concerning problem in California over the last years, stemming from lack of precipitation and snowfall as well as constantly rising temperatures. Many aspects of Californian life including water availability and crop production have been negatively impacted by this recent trend. Due to the significance of agriculture on California, the farming com- munity within California and its consumers, including both in-state consumers and those who California exports its produce to, are at risk to be harmed by the negative impacts of climate change. Significant changes to the state’s temperature, precipitation rate, and water consumption and supply all would have the potential to harm crop production and the agricultural industry. Using the data obtained from various sources for each of these factors, we hope to calculate predicted changes in indemnity losses due to crop production over time. By modeling temperature and precipitation as sinusoidal functions and water consumption as a linear relation to temperature, it becomes possible to predict future indemnity losses based on these factor values using polynomial regression. By passing a moving average filter and eliminating the cyclic nature of the loss function, we were able to deduce that average temperature seemed to increase, average precipitation rate seemed to decrease, and average water consumption also increased. The combination of these factors led to a steady increase in predicted indemnity losses within the next 50 years. As water consumption is the only factor that can be changed through human intervention, it is logical for us to base our recommendations off of it. Agricultural water consumption is the main use of water in the state and a transition into more conservative irrigation methods would allow for a reduction in the net water consumption. Over long periods of time, this would decrease water consumption and therefore indemnity losses based on our models.

Decline in Seasonal Snow during a Projected 20-Year Dry Spell

Snowpack loss in midlatitude mountains is ubiquitously projected by Earth system models, though the magnitudes, persistence, and time horizons of decline vary. Using daily downscaled hydroclimate and snow projections, we examine changes in snow seasonality across the U.S. Pacific Southwest region during a simulated severe 20-year dry spell in the 21st century (2051–2070) developed as part of the 4th California Climate Change Assessment to provide a “stress test” for water resources. Across California’s mountains, substantial declines (30–100% loss) in median peak annual snow water equivalent accompany changes in snow seasonality throughout the region compared to the historic period. We find that 80% of historic seasonal snowpacks transition to ephemeral conditions. Subsetting empirical-statistical wildfire projections for California by snow seasonality transition regions indicates a two-to-four-fold increase in the area burned, consistent with recent observations of high elevation wildfires following extended drought conditions. By analyzing six of the major California snow-fed river systems, we demonstrate snowpack reductions and seasonality transitions result in concomitant declines in annual runoff (47–58% of historical values). The negative impacts to statewide water supply reliability by the projected dry spell will likely be magnified by changes in snowpack seasonality and increased wildfire activity.

Moisture and distribution of a keratophagous moth, Tinea occidentella

Moisture and distribution of a keratophagous moth, <i>Tinea occidentella</i>

Quantifying the electricity, CO2 emissions, and economic tradeoffs of precooling strategies for a single-family home in Southern California*

Abstract High fractions of variable renewable electricity generation have challenged grid management within the balancing authority overseen by the California’s Independent System Operator (CAISO). In the early evening, solar resources tend to diminish as the system approaches peak demand, putting pressure on fast-responding, emissions-intensive natural gas generators. While residential precooling, a strategy intended to shift the timing of air-conditioning usage from peak-demand periods to cheaper off-peak periods, has been touted in the literature as being effective for reducing peak electricity usage and costs, we explore its impact on CO2 emissions in regional grids like CAISO that have large disparities in their daytime versus nighttime emissions intensities. Here we use EnergyPlus to simulate precooling in a typical U.S. single-family home in California climate zone 9 to quantify the impact of precooling on peak electricity usage, CO2 emissions, and residential utility costs. We find that replacing a constant-setpoint cooling schedule with a precooling schedule can reduce peak period electricity consumption by 57% and residential electricity costs by nearly 13%, while also reducing CO2 emissions by 3.5%. These results suggest the traditional benefits of precooling can be achieved with an additional benefit of reducing CO2 emissions in grids with high daytime renewable energy penetrations.

Energy Performance Evaluation of Shallow Ground Source Heat Pumps for Residential Buildings

This paper evaluates the energy performance of shallow ground source heat pumps using the state-of-art whole building energy simulation tool. In particular, the paper presents a systematic and easy to implement approach to model the energy performance of shallow and helical ground heat exchangers and assess their energy efficiency benefits to heat and cool buildings. The modeling approach is based on the implementation of G-functions, generated using a validated numerical model, in a state-of-art whole building energy simulation tool. Both the numerical model and the simulation tool are applied to assess the energy performance of various shallow geothermal systems designed to meet heating and cooling needs for detached single-family homes in California. Specifically, a series of sensitivity analyses is conducted to determine the energy performance of the shallow geothermal systems in 16 locations representing all California climate zones. It is found that the suitability and the efficiency of the shallow geothermal systems vary widely and depend on several factors including their design specifications as well as the climate conditions. Compared with conventional air-to-air heat pumps, the shallow ground source heat pumps can be more energy efficient in most climate zones in California except those locations with extreme weather conditions resulting in either heating or cooling only operation. Moreover, configurations of shallow ground source heat pumps with 16 boreholes with 6.7 m (22 ft) depth are found to be cost-effective in several California climate zones.

The poverty of power in the Green Keynesian turn

This August marked the arrival of a modest step away from climate neoliberalism toward a “green Keynesianism” in the United States. Legislation advanced by the Biden administration shifted away from austerity and carbon market creation, toward patching up public infrastructure and direct industrial subsidies. However, the new program included next to zero labor terms for the private work it would generously subsidize, let alone more active steps to advance public ownership or worker power. The apparent defeat of the novel measures of this Keynesian strategy, by a united corporate front, demonstrates the political peril of a climate transition strategy based on avoiding confrontation with capital. This is especially due to the present confluence of renewable and fossil energy capital, which will have an enduring drive to make use of the enormous remaining fossil reserves worldwide. Political breakthroughs stemming from California's climate transition provide an instructive alternative to Biden's Keynesian indifference to worker power. Through the joint work of scholars, rank-and-file workers, and broader social movements, the racialized and gendered repression of green construction labor must be overcome, if we are to build the power needed for a climate transition that lasts.

캘리포니아주 기후위기법안의 입법정책적 시사점

Korea is actively participating in the solidarity of the international community to reduce greenhouse gas emissions, setting goals for greenhouse gas reduction, forming organizations to be in charge of specific design and implementation, and establishing legal grounds such as legislation. In particular, the Framework Act on Carbon Neutrality has been enacted and is set to take effect, but the abstractness of laws and regulations and individual legislative issues by related fields remain urgent tasks. The California Climate Crisis Act clearly stipulates that the goal of greenhouse gas reduction is about the health and safety of residents, and contains details of greenhouse gas reduction to cope with the climate crisis. In addition, new technical concepts such as carbon dioxide capture, storage, and utilization appearing in the greenhouse gas reduction process are directly defined so that they can serve as clear interpretation criteria for the implementation of legislative purposes. In particular, details on the use of related technologies are specified to help the parties understand. These specific regulations are necessary for enhancing acceptance through the understanding and cooperation of stakeholders such as local residents and related business fields, where confrontation is inevitable in the process of reducing greenhouse gas. Matters related to CCUS, a legislative task stipulated in the Framework Act on Carbon Neutrality, are not only new concepts, but also essential to enhance the acceptance of not only stakeholders in the industry but also the people due to secure stability in the process of technology development and utilization. I hope that the implications of the detailed characteristics of California’s climate crisis legislation in the future can be properly referenced.